The user wants a complete agent harness prototype in TypeScript using Effect (the Effect-TS library), explicitly "effect native" with no async/await — meaning everything should be built with `Effect.gen`, `Effect.tryPromise` avoided where possible, using `Effect.acquireRelease`, `Layer`, `Context.Tag` for DI, fibers, streams, etc. Let me think about what a "complete agent harness" means: - An agent loop: take a user message, call an LLM, parse tool calls, execute tools, feed results back, loop until done - Tool registry with typed schemas (Schema from effect) - LLM client abstraction (could be a mock/fake LLM for prototyping, or an HTTP client to OpenAI/Anthropic — for a prototype, I'll build a provider interface with a mock implementation and maybe show how a real one would plug in) - Conversation/memory management - Streaming support maybe (Effect Stream for token streaming) - Structured logging - Retry/backoff policies - Concurrency control (semaphores) - Cancellation (interruptible) - Budget/step limits - Config layer - Error types (TaggedError with Data.Error) - CLI entrypoint / main - Tests maybe The user says "prototype" so it should be a single coherent codebase, reasonably complete, well-organized. I should write it as multiple files with a project layout, or one big file? For a prototype, showing a project structure with separate modules is better for readability. Let me lay out: ``` agent-harness/ ├── package.json ├── tsconfig.json └── src/ ├── index.ts (main entrypoint) ├── Config.ts (config layer) ├── Errors.ts (domain errors) ├── Logger.ts (logging service) ├── Llm.ts (LLM client service + types) ├── Providers/ │ ├── MockLlm.ts (scripted fake model) │ └── OpenAi.ts (real provider using @effect/platform HttpClient) ├── Tools/ │ ├── Registry.ts (tool registry service) │ ├── builtin/ (echo, time, readFile, httpGet...) ├── Agent.ts (the core loop) ├── Run.ts (run manager, budgets, cancellation) └── Main.ts (CLI wiring / demo) ``` Key Effect idioms to demonstrate: - `Context.Tag` for services (v4 style: `Context.Tag()`) — need to decide Effect version. Effect v3 (current) uses `Context.Tag` class or `Context.Tag()`. Actually in recent Effect versions (3.9+), the recommended is: ```ts class Logger extends Context.Tag("Logger")() {} ``` or the newer: ```ts export class Logger extends Context.Tag("app/Logger")() {} ``` And Schema: `import { Schema } from "effect"` in v3.20+ (Schema moved into effect package). Previously `@effect/schema`. I'll use `effect` v3.13+ style with `Schema` imported from `"effect"`. Let me use the current-ish API: `Schema.Struct`, `Schema.String`, `Schema.decodeUnknown`, `Schema.standardSchemaV1` maybe. For tool definitions: each tool has a name, description, parameters Schema, and a handler `(input: A) => Effect`. LLM message types: role: system/user/assistant/tool, content. Tool calls with id/name/arguments (JSON). The agent loop: ``` run(goal) -> loop(state): response <- llm.complete(messages, tools) if response.toolCalls.isEmpty -> return final text else execute tool calls (with concurrency, timeout, retries), append tool results, loop (respect maxSteps) ``` Demonstrate: - `Effect.gen` with `yield*` - `Effect.service` / `yield* Agent` style via Context.Tag - `Effect.retry` with `Schedule.exponential` + `Schedule.jittered` - `Effect.timeout` - `Effect.forEach` with `concurrency` - `Semaphore` for tool execution limits - `Ref` for conversation state - `Effect.acquireRelease` for lifecycle - `Stream` for token streaming from LLM (Stream.fromAsyncIterable is async but it's inside the library — user said no async/await in our code; using platform HttpClient gives `Effect` responses; streaming response body via `response.stream`). - `Fiber` for cancellation: run agent as fiber, Ctrl+C interrupt. - `Cause` handling at main. - `Layer` composition: `Layer.mergeAll`, `Layer.provide`. - `Config` from `effect/Config`. - Tracing/spans: `Effect.withSpan`. - Metrics maybe: `Metric.counter` for steps/tool calls. For the real provider, use `@effect/platform` `HttpClient`. To keep prototype runnable without API keys, make Mock the default and include an OpenAI-compatible client (works with Anthropic via base url? Anthropic API differs; I'll do an "OpenAI-compatible chat completions" client which works with OpenAI, Groq, Ollama, etc. — that's the most portable). Use `HttpClient` from `@effect/platform` and `NodeHttpClient` layer in main. Since it's a prototype, tool call argument parsing: LLM returns JSON string args; decode with the tool's Schema using `Schema.decodeUnknown(Schema.parseJson(schema))` — nice pattern: `Schema.parseJson` composes so the string → JSON → struct decode is one pipe. Error model: - `AgentError` variants: `StepLimitExceeded`, `ToolNotFound`, `LlmError`, `ToolExecutionError`, `MalformedToolCall`. - Use `Data.TaggedError`. Run control: - `maxSteps` from config - per-tool timeout - overall run timeout maybe - budget: tokens estimate? Keep simple: step budget + wall clock. CLI: read goal from argv, run, print transcript. Also support `--stream` maybe. Keep it modest. Also a "harness" implies evaluation/batching: maybe include a `Harness.ts` that can run N scenarios concurrently with `Effect.forEach` and collect results, asserting final outputs — that makes it a "harness" rather than just an agent loop. I'll include a small scenario runner with a couple of example scenarios against the Mock LLM. Let me also add a scripted MockLlm that reads a script of responses and can execute JS to decide tool calls — simplest: a list of steps where each step either returns tool calls or final text; the mock needs to see tool results to decide. I'll implement mock as a function `(messages) => Effect` provided as a layer from a script with a counter, or a "stateful script" that returns canned responses in order. For the demo scenarios, canned sequence works: step 1 → tool call echo; step 2 → final answer. Alternatively, a smarter mock: an "echo planner" that looks at the last message: if the last message is user → issue a tool call for a deterministic tool; if last is tool → finish with summary. That makes scenarios deterministic without scripting. I'll implement MockLlm with a script queue — simple and explicit. Streaming: For the real provider, implement `streamComplete` returning `Stream`. To keep the loop simpler, the agent uses non-streaming complete; streaming is exposed for CLI printing. Hmm, that doubles provider surface. For a prototype, maybe skip streaming or include a minimal `streamText` used by CLI. I'll include streaming in the LLM service as optional capability... Actually to keep code focused, I'll do: `Llm` service with `complete` (aggregated) and `stream` (Stream of text deltas for the final answer only). The agent loop uses `complete`. The CLI can use `stream` for display. Maybe simpler: only `complete`, and mention streaming extension. I think including a Stream-based path shows off Effect-ness, which the user wants ("effect native"). Let me include it in the OpenAI provider via `response.stream` and in agent via a `Stream.runCollect` fallback... That adds complexity. Compromise: The `Llm` service interface includes both `complete` and `stream`. Mock implements stream by chunking the scripted text. Agent's `complete` is implemented once generically: `stream` piped through an accumulator that detects tool calls vs text? That's actually how real harnesses work (tool call deltas). Too complex for prototype. Keep `complete` as primitive on the service; `stream` as separate method providers may implement; the agent uses `complete`. CLI demo uses `stream` when provider supports it. Fine. Hmm, actually, let me reconsider scope. The answer needs to be complete but readable. Let me enumerate modules and approximate content: 1. `package.json` — deps: `effect`, `@effect/platform`, `@effect/platform-node`, `effect-cli`? no. `tsx` for running. deps versions: effect ^3.x. 2. `tsconfig.json` — strict, `moduleResolution: "bundler"` or nodenext. 3. `src/Domain.ts` — messages, tool calls, completions, ids. 4. `src/Errors.ts` — Data.TaggedError classes. 5. `src/Config.ts` — Config service or direct `Config.string` etc. Use Effect's `Config` module with a layer that reads env. Show `Config.redacted` for API key. 6. `src/Logger.ts` — logger service built on `Logger` module? Effect has a built-in logger; simplest: use built-in `Effect.log*` with a custom logger layer in main. To show DI, define a `Console`-ish? I'll rely on Effect's structured logging (`Effect.logWithLevel`, spans) and add `Logger.removeLogger` default? Keep built-in logging; annotate with `Effect.withLogSpan` / `Effect.annotateLogs`. That's effect-native and less code. Yes: use built-in logger + annotations + spans. 7. `src/Tools.ts` — Tool interface + registry Tag + builders + builtins (echo, now/clock time, readFile, httpGet using platform HttpClient, calculate maybe). Registry: `Ref>` or just an immutable object; service exposing `get`, `list`, `schemasForLlm`. Concurrency limit per tool exec via Semaphore in Agent. 8. `src/Llm.ts` — service Tag: `complete(req): Effect`; request includes messages, tools (name+json schema), temperature, maxTokens. 9. `src/providers/Mock.ts` — scripted. 10. `src/providers/OpenAI.ts` — real HTTP with `HttpClient`, `Schema` decoding of response, retries via schedule, timeouts. Include streaming `stream` using `Sse`? Parsing SSE manually from response.stream: split on newlines, parse `data:` lines. Doable with `Stream` combinators: `Stream.decodeText`, `Stream.splitLines`, filter data lines, drop `[DONE]`, parse JSON chunk, extract delta content. I'll write it compactly. 11. `src/Agent.ts` — the loop. Services: Llm, Tools registry, Config (maxSteps, timeouts). State: messages Ref. Steps with `Effect.iterate` or recursive gen loop with `while` inside `Effect.gen` (allowed — gen body is plain JS, but recursion/while with yield* works). Use `Loop` via `Effect.iterate` maybe cleaner: ```ts Effect.iterate(initial, (s) => pipe(... Effect.map(cont => cont ? Option.some(next) : Option.none()))) ``` Or just write a recursive `step` function returning `Effect` with `Effect.suspend` to avoid stack. Recursion in Effect is fine (stack-safe via flatMap chains are stack safe because of runtime). Use `Effect.suspend(() => loop(...))`. Also: interruption for overall deadline: wrap in `Effect.timeout` at Run level. Tool execution: for each tool call: look up tool, decode args with `Schema.decodeUnknown(Schema.parseJson(tool.parameterSchema))` — note args come as string; some providers give object; handle both: `Schema.is`... simpler: define args as `string` (JSON), decode with parseJson; if provider gave object, stringify first. I'll normalize: `typeof args === "string" ? args : JSON.stringify(args)`. Execute with `tool.run(args)` + `Effect.timeout(tool.timeout)` + retry policy for transient. Collect `ToolResult` message with `tool_call_id`. Errors → tool result message with `isError: true` so the model can recover (harness behavior). Malformed tool call → error tool result. Concurrency: `Effect.forEach(calls, runOne, { concurrency: config.toolConcurrency })` — demonstrates concurrency option; also a global `Semaphore` could be used, forEach concurrency suffices. Metrics: `Metric.counter("agent_steps")`, `Metric.increment` each loop; tool calls counter; `Metric.trackDuration`? Keep two counters + maybe gauge of active runs. Light. Spans: `Effect.withSpan("agent.step", { attributes: { step } })`, root span `agent.run`. 12. `src/Harness.ts` — scenario type: { name, goal, script(mock), expect: (result) => boolean }, `runScenarios` with `Effect.forEach({concurrency: "unbounded"})`, summary of pass/fail, exit code. This is the "harness" part. 13. `src/Main.ts` — parse argv: if `--demo` run scenarios; else run CLI goal with provider chosen by env (`OPENAI_API_KEY` → OpenAI else Mock). Build layers, `NodeRuntime`/`NodeHttpClient.layer`, run with `Effect.runPromise`? "no async/await" — runPromise isn't async/await, it's an effect-runtime entry; acceptable. Or use `NodeRuntime.runMain` from `@effect/platform-node` which handles signals & pretty cause. Use `import { NodeRuntime, NodeContext } from "@effect/platform-node"` and `NodeRuntime.runMain(effect)`? The typical: ```ts import { NodeContext, NodeRuntime } from "@effect/platform-node" NodeRuntime.runMain(app.pipe(Effect.provide(NodeContext.layer))) ``` That handles Ctrl+C interrupts and pretty-prints causes. Cancellation demo: `setTimeout`? We can add graceful shutdown hook: on SIGINT interrupt. NodeRuntime handles that. Also show a `Fiber` usage: run agent and a watchdog fiber that interrupts after deadline; or use `Effect.timeout` which uses interruption internally — fine. Let me now write the actual code carefully with correct Effect v3 APIs. Imports (effect v3): - `import { Context, Data, Effect, Layer, Option, Ref, Schedule, Duration, Schema, Stream, Chunk, Metric, Config, pipe, Exit, Cause, Match, Predicate, Function as F, ManagedRuntime, Fiber, Semaphore, Array as A, Redacted } from "effect"` Note: `Semaphore` in effect v3.9+: `Semaphore.make(n)` returns Effect? Actually `Effect.makeSemaphore(n)` returns `[semaphore, release]`? In v3, `Effect.makeSemaphore` returns `Effect`? Let me recall: `Effect.makeSemaphore = (permits) => Effect.sync(...)` returns Effect. And `Semaphore` type is in `effect/Effect` (Effect.Semaphore). There's also `effect/Semaphore`? Hmm. In Effect v3, `Effect.makeSemaphore` exists returning `Effect`; `Semaphore` interface has `withPermits(n): (self) => Effect` (older) or in newer versions `withPermits` takes the effect... In recent versions (3.13+), `Effect.makeSemaphore` deprecated in favor of `import { Semaphore } from "effect"` with `Semaphore.unsafeMake`? To avoid API drift risk, safer: use `Effect.forEach(..., { concurrency })` only, and implement per-tool semaphore via `Effect.withConcurrency`? For tool execution we use forEach concurrency — enough. I'll skip explicit Semaphore to reduce risk, or include a simple `Queue`-based? Skip. Use forEach concurrency: unbounded? bounded N. Good. Schema APIs (effect v3 recent): `Schema.Struct({...})`, `Schema.String`, `Schema.Number`, `Schema.optional`, `Schema.Union`, `Schema.Literal`. For JSON parse: `Schema.parseJson(Schema)` composes: `Schema.parseJson()` returns Schema; `Schema.parseJson(schema)`? In v3, `Schema.parseJson(schema)` isn't a combinator... Actually it is: `Schema.parseJson(Schema.Type)`? The API: `Schema.parseJson: (schema: Schema, options?) => SchemaClass` — yes, `Schema.parseJson(schema)` exists producing decoding from string. Also `Schema.decodeUnknown(schema)` returns `(u: unknown) => Effect`. And `Schema.decode` for typed input. And `Schema.isEmptyString`? Not needed. For encoding tool schemas to JSON Schema for the LLM: In effect v3 there's `JSONSchema` module: `JSONSchema.fromSchema(schema)`? There's `import { JSONSchema } from "effect"` and `JSONSchema.fromSchema(schema)` returning `JSONSchema7`-ish. It exists in `effect/JSONSchema` (moved from @effect/schema). I'll use it; wrap in try? It's pure. Signature: `JSONSchema.fromSchema(schema, { definitions? })` returns `object`? It returns `JSONSchema7`. Good enough; if drift, prototype-acceptable. To be safe, I could write a tiny fallback... No—use it directly; it's current. OpenAI provider with `HttpClient`: ```ts import { HttpClient, HttpClientRequest, HttpClientResponse } from "@effect/platform" ``` Usage: ```ts const res = yield* HttpClient.execute( HttpClientRequest.post(`${baseUrl}/chat/completions`).pipe( HttpClientRequest.bodyJson({...}), // returns request HttpClientRequest.bearerToken(key) // Redacted? bearerToken accepts string; use Redacted.value ) ) const json = yield* res.json // Effect ``` `HttpClientResponse.schema`? There's `HttpClientResponse.schema(schema)`? There's `HttpClientResponse.schemaBodyJson(schema)`? Hmm: In @effect/platform, `HttpClientResponse` has `schemaBodyJson(schema)` returning `(response) => Effect`? Actually `HttpClientResponse.schemaBodyJson` exists: `HttpClientResponse.schemaBodyJson(MySchema)(response)`. There's also newer `HttpClient.execute` returns `Effect` with methods. For robustness across versions, I'll use `res.json` then `Schema.decodeUnknown(ResponseSchema)` — stable API. Good. Also filter status: `HttpClientResponse.filterStatusOk(res)`? There's `HttpClientResponse.filterStatusOk` giving error if non-2xx. In newer versions there's `HttpClient.filterStatusOk` applied to effect. I'll do manual: if `res.status >= 400` → fail with LlmError including body text. Read body: `yield* res.text`. Use that for both ok and error to include details. Streaming SSE: `res.stream` is `Stream`. Then: ```ts res.stream.pipe( Stream.decodeText(), Stream.splitLines, Stream.filter(l => l.startsWith("data: ")), Stream.map(l => l.slice(6)), Stream.filter(l => l !== "[DONE]"), Stream.map(...parse json, extract choices[0].delta.content), Stream.flattenIterables, // since content may be undefined → empty ) ``` Parse inside map returning Either then `Stream.collectWhile`? Simpler: `Stream.map(parseChunk)` where parseChunk returns string[] and `Stream.flattenIterables`. Parsing errors → emit empty. Fine for prototype. Mock provider: script: `ReadonlyArray` where `MockStep = { type: "message", content } | { type: "tool_calls", calls }`... But completions must match our `Completion` shape: either text final or tool calls. I'll define: ```ts export type MockStep = | { readonly _tag: "Text"; readonly text: string } | { readonly _tag: "ToolCalls"; readonly calls: ReadonlyArray } ``` with `MockCall = { name: string; args: unknown }` and the service generates ids `call_1`... Keep a `Ref` for step index; when script exhausted → return final "Mock script exhausted" or fail with LlmError. Also assert? The harness scenarios include expected final text. Tool builtins: - `echo` { message } → returns message (sanity). - `clock.now` → ISO time via `Effect.clock` `Clock.currentTimeMillis`. - `fs.readFile` { path } with `NodeFs`? Using @effect/platform `FileSystem` service — effect-native: `yield* FileSystem.readFile(path)`. Guard path traversal? Prototype: allow but note. Include `maxBytes`? Keep simple, catch errors → tool error result. - `http.getText` { url } via `HttpClient.execute(HttpClientRequest.get(url))` then `res.text`, with `Effect.timeout`. - `math.eval`? Implement tiny safe arithmetic evaluator? Could use `Function`... no eval. Provide `math.add`? Meh. Better: `json.query`? Keep four tools: echo, clock.now, fs.read, http.get. Maybe `text.uppercase`? Not needed. Actually a fun one for demo: `fs.stat`? Skip. Wait — tools require platform services (FileSystem, HttpClient) in their R. The registry service stores tools with their R; the Agent's R includes union. Typed: `Tool` with `run: (input: A) => Effect`. Registry `ToolRegistry` service type has `Effect<...>` methods with R = ToolServices... To keep the tag simple, define registry over `Tool`? That loses typing but acceptable in prototype with a note. Alternatively parameterize registry by `R` union: `class ToolRegistry extends Context.Tag(...)()` where `RegistryShape = { get(name): Option; list(): Array; withToolServices: (e: Effect) => Effect }`. Hmm. Simplest pragmatic approach: define `Tool` as: ```ts export interface Tool { readonly name: string readonly description: string readonly parameters: Schema.Schema // encode to json readonly run: (input: I) => Effect.Effect } ``` where `ToolEnv = FileSystem | HttpClient` (concrete union of what builtins need). That fixes R to a known union — pragmatic and keeps everything concrete. New tools needing more deps would widen this alias. For prototype: fine, and I'll note it. Actually even simpler and cleaner: each tool's run returns `Effect` by *escaping* requirements inside the tool implementation? No — tools need services. Keep `ToolEnv` union. In Agent, `yield*` requires those in R; Main provides `NodeContext.layer` + `NodeHttpClient.layer`. Registry: ```ts export class ToolRegistry extends Context.Tag("harness/ToolRegistry") Effect readonly get: (name: string) => Effect> readonly all: () => Effect> }>() {} ``` Built as `Layer` from `Ref`: ```ts export const layerWith = (tools: ReadonlyArray) => Layer.effect(ToolRegistry, Effect.gen(function* () { const ref = yield* Ref.make(HashMap.empty()) ... })) ``` Use `HashMap` for flair or plain Record. `Ref.make(new Map(...))`? Ref with Map mutation is unsafe (Ref updates should be pure; using immutable). Use `Ref.make>` and `Ref.update`. Agent loop detail: ```ts export class Agent extends Context.Tag("harness/Agent")() {} type AgentShape = { readonly run: (goal: string) => Effect } ``` Hmm — Agent's run R should include ToolEnv because it executes tools. But then Agent service shape R includes ToolEnv... Context.Tag shape methods can have R. Then Main provides everything. Fine. AgentShape maybe also `runFork` for cancellation demo? Keep `run`. Implementation sketch: ```ts export const AgentLive = Layer.effect(Agent, Effect.gen(function* () { const llm = yield* Llm const tools = yield* ToolRegistry const cfg = yield* HarnessConfig const run = (goal: string) => Effect.gen(function* () { const messages: Array = [] const push = (m: Message) => Effect.sync(() => { messages.push(m) }) // or Ref yield* push({ role: "user", content: goal }) let steps = 0 const toolCallsMade = ... while (true) { steps++ if (steps > cfg.maxSteps) return yield* Effect.fail(new StepLimitExceeded({ steps: cfg.maxSteps })) const completion = yield* llm.complete({ messages, tools: yield* toolSchemas }).pipe( Effect.withSpan("agent.step", { attributes: { step: steps } }), Effect.retry(llmPolicy) ) // metric yield* Metric.increment(stepsCounter) if (completion.toolCalls.length === 0) { yield* push({ role: "assistant", content: completion.text }) return { finalText: completion.text, steps, messages } } yield* push({ role: "assistant", content: completion.text ?? "", toolCalls: completion.toolCalls }) const results = yield* Effect.forEach(completion.toolCalls, execTool, { concurrency: cfg.toolConcurrency, discard: false }) for (const r of results) yield* push(r) } }).pipe(Effect.withSpan("agent.run")) })) ``` execTool: ```ts const execTool = (call: ToolCall) => Effect.gen(function* () { const toolOpt = yield* tools.get(call.name) if (Option.isNone(toolOpt)) return toolErr(call, `unknown tool ${call.name}`) const tool = toolOpt.value // decode args const decoded = yield* decodeArgs(tool, call.arguments).pipe(Effect.either) if (Either.isLeft(decoded)) return toolErr(call, `bad args: ${...}`) const out = yield* tool.run(decoded.right).pipe( Effect.timeout(cfg.toolTimeout), Effect.catchAll(e => Effect.succeed(ToolOutput.fail(String(e)))), Effect.withSpan("tool." + call.name) ) return { role: "tool", toolCallId: call.id, content: JSON.stringify(out), isError: out.success === false } as Message }).pipe(Effect.catchAllDefect(...)) ``` Wait — `Effect.catchAll` on tool.run with R=ToolEnv: catchAll keeps R. fine. But note `Effect.timeout` failure is a `TimeoutException` — catchAll captures. But careful: catchAll must catch all error channel types: tool.run errors are `unknown`? Define tool errors as `ToolFailure` type? Tools may fail with any error (ParseError, HttpClientError, FsError...). So type run's error channel as `ToolRuntimeError` union? Pragmatic: `Effect`? unknown error channel is awkward with catchAll (needs `Effect.catchAll` accepting unknown — fine: `(e: unknown) => ...`). Effect allows error type unknown with catchAll handler taking unknown. OK. Define ToolOutput: ```ts export type ToolOutput = { readonly success: true; readonly value: unknown } | { readonly success: false; readonly error: string } ``` Or simpler: tools return `string` (the observation). Most harnesses: tool returns JSON-serializable output; error → isError message. I'll have run return `Effect` and execTool stringifies: success → `JSON.stringify({ ok: true, result })`, error → `{ ok: false, error: String(e) }` with `isError: true`. Simple. decodeArgs: `call.arguments` is `unknown` (string | object). Normalize then `Schema.decodeUnknown(Schema.parseJson(tool.parameters))` if string; if object, `Schema.decodeUnknown(tool.parameters)`. Implementation: ```ts const decodeArgs = (tool: Tool.Any, args: unknown) => { if (typeof args === "string") return Schema.decodeUnknown(Schema.parseJson(tool.parameters))(args) return Schema.decodeUnknown(tool.parameters)(args) } ``` But Tool is generic over I... With `Tool.Any = Tool`, parameters: `Schema.Schema`? Schema generics: `Schema.Schema`? Note Schema type params order: `Schema` where A is type, I is encoded. `Schema.Struct({...})` gives `SchemaClass<{...}, {...}, never>`. For a tool storing schema for arbitrary I, declare `parameters: Schema.Schema`? Hmm decodeUnknown(schema) returns Effect. If schema is `Schema.Schema` then decode gives I. With Any alias `Tool` we get any. fine. JSON Schema for LLM: `JSONSchema.fromSchema(tool.parameters)`. But our Tool parameters include `type: "object"` struct so fine. Message types: ```ts export type ToolCall = { readonly id: string; readonly name: string; readonly arguments: unknown } export type Message = | { readonly role: "system"; readonly content: string } | { readonly role: "user"; readonly content: string } | { readonly role: "assistant"; readonly content: string; readonly toolCalls?: ReadonlyArray } | { readonly role: "tool"; readonly toolCallId: string; readonly content: string; readonly isError?: boolean } ``` Completion: ```ts export interface Completion { readonly text: string readonly toolCalls: ReadonlyArray readonly finishReason: string readonly usage?: { in: number; out: number } } ``` Llm service: ```ts export class Llm extends Context.Tag("harness/Llm") Effect readonly stream?: (req: ChatRequest) => Stream.Stream }>() {} ``` Making stream optional complicates; define both required, Mock implements stream by chunking text. OK. ChatRequest: `{ messages, tools: Array<{ name, description, parameters: object }>, temperature?, maxTokens? }`. Errors with Data.TaggedError: ```ts export class LlmError extends Data.TaggedError("LlmError")<{ readonly reason: string; readonly status?: number; readonly cause?: unknown }> {} export class StepLimitExceeded extends Data.TaggedError("StepLimitExceeded")<{ readonly maxSteps: number }> {} export class AgentAborted extends ...? not needed (interruption handled by runtime) export class ScenarioFailure extends Data.TaggedError("ScenarioFailure")<{ name: string; detail: string }> {} ``` Config service: I'll create `HarnessConfig` Tag with fields: maxSteps, toolTimeout (Duration), toolConcurrency, requestTimeout, model, baseUrl, apiKey (Redacted). Built via Layer from Effect Config: ```ts export class HarnessConfig extends Context.Tag("harness/Config")() {} export const ConfigLive = Layer.effect(HarnessConfig, Effect.all({ maxSteps: Config.integer("AGENT_MAX_STEPS").pipe(Config.withDefault(12)), ... model: Config.string("AGENT_MODEL").pipe(Config.withDefault("gpt-4o-mini")), baseUrl: Config.string("AGENT_BASE_URL").pipe(Config.withDefault("https://api.openai.com/v1")), apiKey: Config.redacted("OPENAI_API_KEY") // optional? })) ``` Config.redacted fails if missing; use `Config.option(Config.redacted(...))` for Option. Good — shows Redacted. MockLlm layer: ```ts export const layer = (script: ReadonlyArray) => Layer.effect(Llm, Effect.gen(function*() { const idx = yield* Ref.make(0) return { complete: (req) => Effect.gen(function*(){ const i = yield* Ref.getAndUpdate(idx, n => n + 1) const step = script[i] ?? { _tag: "Text", text: "Mock script exhausted." } return toCompletion(step) }), stream: (req) => Stream.unwrap(Effect.map(currentStep, s => Stream.make(...chunkText(s)))) } })) ``` OpenAI provider: ```ts export const layer = Layer.effect(Llm, Effect.gen(function* () { const http = yield* HttpClient const cfg = yield* HarnessConfig const complete = (req: ChatRequest) => Effect.gen(function* () { const body = { model: cfg.model, messages: req.messages.map(encodeMessage), tools: req.tools.map(encodeTool), temperature: req.temperature ?? 0.2 } const res = yield* http.execute( HttpClientRequest.post(cfg.baseUrl + "/chat/completions").pipe( HttpClientRequest.bodyJson(body), Option.isSome(cfg.apiKey) ? HttpClientRequest.bearerToken(Redacted.value(cfg.apiKey.value)) : identity ) ) const text = yield* res.text if (res.status >= 400) return yield* Effect.fail(new LlmError({ reason: `HTTP ${res.status}: ${text.slice(0,300)}`, status: res.status })) const decoded = yield* Schema.decodeUnknown(ApiResponse)(text) // parseJson built into schema return toCompletion(decoded) }) return { complete, stream: (req) => Stream.suspend(() => streamChat(http, cfg, req)) } })) ``` Careful: `HttpClientRequest.bodyJson(body)` — in @effect/platform, `HttpClientRequest.bodyJson` returns `Effect`? Hmm. Actually `HttpClientRequest.bodyJson = (json: unknown): Effect`? Let me recall... In @effect/platform v3.x, `HttpClientRequest.bodyJson` returns `HttpClientRequest` directly? I believe there was a change: earlier it returned Effect; then `HttpClientRequest.bodyJson` became... Checking memory: The module `HttpClientRequest` has combinators like `.pipe(HttpClientRequest.bodyJson({...}))`. I recall `bodyJson` returns `Effect`... Hmm, I genuinely recall that `HttpClientRequest.bodyJson` returns an `Effect` because JSON.stringify can throw. Wait no — JSON.stringify of arbitrary value could throw (circular), so they made it Effect? Let me think of usage examples from docs: ```ts const request = HttpClientRequest.post("https://api.example.com").pipe( HttpClientRequest.bodyJson({ key: "value" }) ) ``` I've seen examples like that treating it as request directly. But I've also seen `yield* HttpClientRequest.bodyJson(...)`. In recent versions, I believe `HttpClientRequest.bodyJson` returns `HttpClientRequest` (it uses `JSON.stringify` wrapped? or maybe it's safe now?). Hmm. Actually I now recall: `HttpClientRequest.bodyJson` returns `Effect`? There is `Effect.try` wrap... Let me check my memory of the source: packages/platform/src/HttpClientRequest.ts: ```ts export const bodyJson: (json: unknown) => Effect = ... ``` Hmm. I remember `HttpClientRequest.bodyUrlParams` returns request. For bodyJson I'm fairly sure it's an Effect in current versions — no wait. In the current docs (effect.website /platform/http-client): ```ts import { HttpClientRequest } from "@effect/platform" const req = HttpClientRequest.post("/").pipe(HttpClientRequest.bodyJson({ a: 1 })) ``` Hmm I really can't be 100% sure. Alternative that's unambiguous: build body string myself: ```ts HttpClientRequest.post(url).pipe( HttpClientRequest.bodyUnsafe("application/json", JSON.stringify(body)), // hmm ) ``` There's `HttpClientRequest.body = (body: Body)` and `Body.unsafeJson`, `Body.json` (Effect?). To be safe: use `HttpClientRequest.bodyRaw`? Meh. Safest cross-version approach: ```ts HttpClientRequest.post(url).pipe( HttpClientRequest.setHeader("content-type", "application/json"), HttpClientRequest.bodyUnsafe("application/json", JSON.stringify(body)) ) ``` Does `bodyUnsafe` exist? I recall `HttpClientRequest.bodyUnsafe = (contentType: string, content: string | ArrayBuffer...): HttpClientRequest`. Hmm, I think `Body.unsafeJson` exists and `HttpClientRequest.bodyUnsafe` exists too. I'm fairly confident about `HttpClientRequest.bodyUnsafe(contentType, content)` existing (it's used in tests). Alternatively `HttpClientRequest.bodyText(text, { contentType })`? There's `HttpClientRequest.bodyText(text)` sets text/plain... Alternative clean approach avoiding doubt: construct via `HttpClientRequest.make("POST")(url)` then `.pipe(HttpClientRequest.body(...))`... still Body question. OK here's another approach that's definitely stable: use `HttpClientRequest.post(url)` and then set body using `HttpClientRequest.bodyJson` **as an Effect** if it returns Effect — the risk is compile error if it's sync. Choose one. Let me actually recall the source (effect v3.12 HttpClientRequest.ts): I recall: ```ts export const bodyJson = (json: unknown): Effect => ... ``` Hmm... And there's `Body.json`? In Body module: `Body.unsafeJson: (json: unknown) => Body`, `Body.json: (json) => Effect`? I think Body.json doesn't exist; there's `Body.unsafeJson`. And HttpClientRequest.bodyJson — I now more strongly recall it returns `HttpClientRequest` directly? Let me search memory of docs page "HttpClient": example: ```ts const program = Effect.gen(function* () { const client = yield* HttpClient const response = yield* client.execute( HttpClientRequest.post("https://api.example.com/submit").pipe( HttpClientRequest.bodyJson({ id: 1 }) ) ) }) ``` I've definitely seen this exact style in recent docs where bodyJson is used inside pipe returning a request. Hmm, but I've also seen: ```ts const request = yield* HttpClientRequest.post("...").pipe(HttpClientRequest.bodyJson(data)) ``` in older versions. There was indeed a change at some point (2024) where `bodyJson` changed from Effect-returning to sync? Or reverse? Given uncertainty, pick the approach immune to it: JSON-encode manually and use a text body with content-type header: ```ts const payload = JSON.stringify(body) const req = HttpClientRequest.post(`${baseUrl}/chat/completions`).pipe( HttpClientRequest.bodyUnsafe("application/json", payload), HttpClientRequest.bearerToken(Redacted.value(key)) ) ``` I'm quite confident `HttpClientRequest.bodyUnsafe` exists (signature `(contentType: string, content: string | ArrayBuffer | Uint8Array) => HttpClientRequest`). Yes — I remember `bodyUnsafe` from the source. It's less commonly shown but stable. I'll use that. If paranoid, could also do `HttpClientRequest.bodyText(payload)` + header — bodyText sets content-type text/plain unless options; `bodyText(text, { contentType })`? not sure about options param. Use bodyUnsafe. Bearer: `HttpClientRequest.bearerToken(token: string)` — exists. With Redacted: `Redacted.value(cfg.apiKey)`. In effect v3.12+, Redacted replaced Secret. Use Redacted. Config.redacted returns Config. Good. Response schema: ```ts const ApiChatMessage = Schema.Struct({ role: Schema.Literal("assistant"), content: Schema.NullOr(Schema.String), tool_calls: Schema.optional(Schema.Array(Schema.Struct({ id: Schema.String, type: Schema.Literal("function"), function: Schema.Struct({ name: Schema.String, arguments: Schema.String }) }))) }) const ApiResponse = Schema.Struct({ choices: Schema.Array(Schema.Struct({ finish_reason: Schema.optional(Schema.String), message: ApiChatMessage })), usage: Schema.optional(Schema.Struct({ prompt_tokens: Schema.Number, completion_tokens: Schema.Number })) }) ``` Decode with `Schema.decodeUnknown(Schema.parseJson(ApiResponse))(text)` — parseJson from string. Good. toCompletion maps tool_calls (optional array) → ToolCall[] with arguments kept as string (agent decodes later). content "" when null. Streaming: implement with Stream: ```ts const stream = (req: ChatRequest): Stream.Stream => Stream.suspend(() => { const payload = JSON.stringify({ ...bodyOf(req), stream: true }) const req_ = HttpClientRequest.post(url).pipe(HttpClientRequest.bodyUnsafe("application/json", payload), auth) return http.execute(req_).pipe( Effect.map(res => res.stream), Stream.unwrapEffect, Stream.decodeText(), Stream.splitLines, Stream.filterMap(line => { if (!line.startsWith("data: ")) return Option.none() const data = line.slice(6).trim() if (data === "[DONE]") return Option.none() return parseDelta(data) // Option }), Stream.mapError(e => new LlmError({ reason: String(e) })) ) }) ``` parseDelta: try JSON.parse, get `choices[0].delta.content` string else none. Note also SSE lines could be `data:{...}` without space; handle by trimming prefix "data:" then trim. Fine. Errors from res.stream are ResponseError; mapError covers. Also need status check for streaming? skip for prototype (or wrap). OK. Also add retry policy at Llm level in Agent: `Schedule.exponential("200 millis").pipe(Schedule.compose(Schedule.recurs(3)), Schedule.jittered)` with `Effect.retry` — but retrying on LlmError always may be wrong for 4xx; use `Effect.retry` with schedule and also `Effect.retry` respects... For prototype fine; or use `Schedule.intersect`? Keep: retry up to 3 times, exponential, only on LlmError (all). Mention transient filter in comment. Harness scenarios: define ```ts export interface Scenario { readonly name: string readonly goal: string readonly script: ReadonlyArray readonly expect: (r: AgentResult) => boolean } ``` `runScenario(s)` builds layers: MockLlm.layer(s.script) + ToolRegistry.layerWith(builtins) + Config defaults + Agent.live; then `Agent.run(s.goal)` and check expect; return { name, ok, detail }. `runAll` with Effect.forEach concurrency unbounded (demonstrates fibers) then print table, exit code via `Process.exit`? In Node: `Effect.sync(() => process.exit(...))` or return exit code and let main do `NodeRuntime.runMain`? runMain doesn't set exit code from value. Use `Process`? platform-node has `NodeContext`... Simplest: `Effect.sync(() => { process.exitCode = ok ? 0 : 1 })`. Acceptable (Node-specific bit in Main). Or `ExitCode`... keep process.exitCode. Main.ts: ```ts const goal = process.argv.slice(2).join(" ") // or from commander? no deps: manual const useOpenAI = Option.isSome(envKey) // via Config in layer... but choosing provider requires reading config before layers built. Alternative: always provide both layers? Llm Tag single service. Use config: AGENT_PROVIDER=mock|openai default: mock unless OPENAI_API_KEY set. Read via Effect Config in main gen, then Effect.provide appropriate layer (Layer.unwrapEffect!). Nice idiom: const LlmLive = Layer.unwrapEffect(Effect.map(Config.string("AGENT_PROVIDER").pipe(Config.withDefault("mock")), p => p === "openai" ? OpenAi.layer : Mock.layerDefault)) ``` But Mock needs script; default script = demo script that does tool call then finish? For CLI with real goal, mock is silly but fine for prototype (echo tool). Also `--demo` flag to run harness scenarios. Parse argv in main gen: `Effect.sync(() => process.argv.slice(2))`. Wire layers: ```ts const HttpLive = NodeHttpClient.layerUndici (or NodeHttpClient.layer) const app = Effect.gen(...).pipe( Effect.provide(Layers.all) // compose ) NodeRuntime.runMain(app) ``` NodeHttpClient.layer uses fetch-based? There are `NodeHttpClient.layer` (undici) and `layerUndici`? In current @effect/platform-node: `NodeHttpClient.layer` (undici-based) and `NodeHttpClient.layerUndici`? I recall `NodeHttpClient.layerUndici` exists and `NodeHttpClient.layer` uses node http? Actually: `NodeHttpClient.layer` — built on undici? The module exposes `layer`, `layerUndici`, `layerWithoutAgent`... I think: `NodeHttpClient.layer` uses undici's fetch? Hmm. There are three: `layer` (undici-based default), `layerUndici` (undici with agent config?) ... Let me recall: platform-node NodeHttpClient exports: `layer`, `layerUndici`, `layerWithoutAgent`, `layerUndiciWithoutAgent`? I believe the default `NodeHttpClient.layer` is undici-based. To be safe, use `NodeHttpClient.layer`. That's the commonly used one in docs. FileSystem: `NodeFileSystem.layer` from `@effect/platform-node`. NodeContext.layer provides FileSystem, Path, etc all together — use `NodeContext.layer` which includes Http? NodeContext.layer includes: FileSystem, Path, Terminal, Clock? It provides platform node services (Etag, FileSystem, Path, ...) but NOT HttpClient I think. Docs: `NodeContext.layer` gives `FileSystem`, `Path`, `Terminal`, `Runtime`, ... HttpClient needs `NodeHttpClient.layer`. I'll provide both: `Layer.mergeAll(NodeContext.layer, NodeHttpClient.layer, NodeFileSystem.layer...)` — NodeFileSystem included in NodeContext? NodeContext.layer includes NodeFileSystem? I think NodeContext.layer = FileSystem + Path + Terminal + Runtime + ... yes it includes FileSystem (NodeFileSystem.layer). To be explicit and safe, provide `NodeFileSystem.layer` too via merge (duplicate provisions fine if same tag? merging layers that both provide same tag — later wins? Could error?). Layer.mergeAll with duplicates might produce "service already initialized"? Actually mergeAll just merges context; duplicate tags from different layers could conflict... Safer: `NodeContext.layer` alone + `NodeHttpClient.layer`. And ensure builtins only need FileSystem/Path/HttpClient/Clock — all in NodeContext? Path yes; Clock is built into default runtime. Terminal not needed. Hmm wait, does NodeContext.layer include HttpClient? I don't believe so. Keep NodeHttpClient.layer merged. Also `NodeRuntime.runMain(main)` — signature `runMain(effect: Effect, options?)`. Also `NodeRuntime.runMain({ disableErrorReporting?: boolean }, effect)`? There's `NodeRuntime.runMain` and `NodeRuntime.runFork`. Use runMain. It handles SIGINT → interrupt (interruption demo). Also sets exit code on failure & pretty-prints defects via built-in logger. Demo of Fiber: In Agent or Run module, provide `runWithDeadline` using `Effect.race` or fork a watchdog: Actually a nice effect-native showcase: overall deadline via forked watchdog: ```ts const withDeadline = (e: Effect, d: Duration.Duration) => Effect.gen(function* () { const fiber = yield* Effect.fork(e) const res = yield* Effect.raceFirst( fiber.join, Effect.sleep(d).pipe(Effect.andThen(Effect.fail(new AgentAborted(...)))) ) ... }) ``` That's clunky; `Effect.timeout` is the idiomatic way and it *is* interruption under the hood. I'll use `Effect.timeout` for run-level deadline and mention it interrupts fibers (tools/llm) — demonstrates cancellation without custom fiber code. Maybe still show one explicit Fiber usage: in Harness, run scenarios concurrently — that's forEach concurrency (fibers internally). And a `Ref`-based progress ticker fiber for CLI: fork a fiber printing "elapsed..." every 2s, interrupted via `Fiber.interrupt` in acquireRelease — nice showcase of fiber lifecycle! Add small `RunStatus` ticker in CLI: ```ts const ticker = Effect.gen(...loop sleep + log steps so far...).pipe(Effect.repeat(...)) Effect.acquireUseRelease(Effect.forkDaemon(ticker), _ => agentRun, fiber => Fiber.interrupt(fiber)) ``` Good — demonstrates forkDaemon + Fiber.interrupt. Or use `Effect.forEach` with... fine. Where to keep step counter for ticker? Agent publishes progress via... a `Ref` in a small `Progress` service or PubSub? Could use `Metric` gauge read? Simpler: Agent appends to messages array; ticker can't access. Add `Progress` service with `Ref<{ steps: number; toolCalls: number }>`? That's extra code; maybe skip ticker to control length. The answer is already large. I'll include a minimal `progress` PubSub? Hmm. Let me instead show Fiber + PubSub lightly: Agent emits events into a `PubSub` (stream!) — this is very "effect native" and powers both logging and streaming UI. Events: StepStarted, LlmResponse, ToolStarted, ToolFinished, RunFinished. The agent loop publishes; CLI subscribes with `Stream.runForEach` printing; and the run also returns result. This showcases Stream + PubSub + Subscribers. But adds size... I think events are the heart of an "agent harness" (observability). I'll include a compact version: ```ts export type AgentEvent = | { readonly _tag: "RunStarted"; goal: string } | { readonly _tag: "StepStarted"; step: number } | { readonly _tag: "ToolStarted"; step: number; call: ToolCall } | { readonly _tag: "ToolFinished"; step: number; call: ToolCall; ok: boolean; ms: number } | { readonly _tag: "RunFinished"; steps: number; finalText: string } export class Events extends Context.Tag("harness/Events")>() {} ``` Events.layer = `Layer.effect(Events, PubSub.unbounded())`. AgentLive requires Events, publishes with `PubSub.publish`. CLI: `const sub = yield* Events.subscribe` then fork `Stream.fromPubSub(sub)...`? `PubSub.subscribe` returns Effect; `Stream.fromSubscription`? There's `Stream.fromPubSub` / `Stream.fromPubSubSafe`? Hmm: In Effect v3, `PubSub.subscribe: Effect>` and `Stream.fromPubSub`? I recall `Stream.fromPubSub(pubsub)` requires... Actually there's `Stream.fromPubSub(pubsub)`? I believe the API is `Stream.fromPubSub` (needs Scoped subscription) — `Stream.unwrapScoped(Effect.map(PubSub.subscribe(pubsub), Stream.fromQueue))`? PubSub subscription is a Queue; `PubSub.subscribe` acquires resource needing scope. Pattern: ```ts Stream.unwrapScoped(Effect.map(PubSub.subscribe(events), (sub) => Stream.fromQueue(sub))) ``` `Stream.fromQueue` exists (aka fromQueue). And scoped within runForkED... In CLI: ```ts yield* Stream.runForEach(Stream.unwrapScoped(...), e => Effect.log(...)).pipe(Effect.forkScoped/ forkDaemon) ``` within a scope. OK doable but adds complexity; alternatively make Events expose `events: Stream` built with `Stream.unwrapScoped`. Hmm, service with a Stream property — fine. Simplification: Events service exposes `publish(e)` and `subscribe(): Stream` implemented as `Stream.unwrapScoped(Effect.map(PubSub.subscribe(self), Stream.fromQueue))`. Then CLI demo: fork a subscriber that logs events with `Effect.log`. And harness collects events into Ref to assert? Scenario expects could include event assertions. Keep expect(result, events?) simple: expect(result). OK. Now, one more consideration: "no async/await" — I must ensure I don't use async functions anywhere, and avoid `Effect.tryPromise`/`Effect.promise`. For HTTP use platform HttpClient (Effect-native). For fs use platform FileSystem. For setTimeout-ish use `Effect.sleep`. Mock uses no async. In OpenAI streaming, all Stream combinators — no async iterators manually (`Stream.fromAsyncIterable` would use async internally but that's library; still, avoid). Good. Also `Effect.runPromise` at entry? That's not async/await syntax; but even cleaner: `NodeRuntime.runMain` handles it. Let me now also design `Tool.Any` typing more carefully so the registry is heterogeneous. ```ts export interface Tool { readonly name: string readonly description: string readonly parameters: Schema.Schema // I = decoded type readonly run: (input: I) => Effect.Effect } ``` Hmm Schema.Schema — order is (Type, Encoded, R): `Schema`. So `Schema.Schema` means type I, encoded any. If I write `Schema.Schema` then encoded = I (default) — a Struct schema has encoded equal struct too, so `Schema.Schema` works for our tools (all built with Schema.Struct whose type & encoded match). Use `Schema.Schema`. But wait: Schema.Schema as an interface property: `readonly parameters: Schema.Schema` — structural: Schema.Struct({...}) is `SchemaClass` assignable to `Schema`? SchemaClass implements Schema; assignable to Schema only if I = A. For structs with strings/numbers, encoded type equals decoded type (string is string) — yes, `Schema.String` is Schema. Unions of literals: also same. So OK. `Tool.Any = Tool` for registry storage. decode: `Schema.decodeUnknown(tool.parameters)` returns `(u: unknown) => Effect`. parseJson composition for string args: `Schema.decodeUnknown(Schema.parseJson(tool.parameters))` — parseJson(schema: Schema): Schema. With A=any fine. JSON Schema: `JSONSchema.fromSchema(tool.parameters)` — returns `JSONSchema.JSONSchema` object. Type the tool list for LLM: ```ts export interface ToolSpec { readonly name: string; readonly description: string; readonly parameters: unknown /* json schema */ } ``` Now builtins: ```ts const echoTool: Tool<{ message: string }> = { name: "echo", description: "Echoes the message back.", parameters: Schema.Struct({ message: Schema.String }), run: (i) => Effect.succeed(i.message) } ``` clock: ```ts run: () => Effect.map(Clock.currentTimeMillis, ms => new Date(ms).toISOString()) ``` fs.read: ```ts parameters: Schema.Struct({ path: Schema.String }) run: ({path}) => Effect.gen(function*(){ const fs = yield* FileSystem; const buf = yield* fs.readFile(path); const text = buf.toString("utf8").slice(0, MAX) ... }) ``` Buffer typing: platform FileSystem.readFile returns Uint8Array in newer versions (they moved from Buffer to Uint8Array). `new TextDecoder().decode(buf)`. Safe. http.get: ```ts run: ({url}) => Effect.gen(function*(){ const http = yield* HttpClient const res = yield* http.execute(HttpClientRequest.get(url)) const text = yield* res.text return text.slice(0, MAX) }) ``` http error type union — error channel `unknown`? run declared Effect so fine (I set Tool run error type unknown). But then in Agent catchAll `(e: unknown)`. `Effect.timeout` error: TimeoutException; catchAll unknown catches. Good. Also add `Effect.catchAllDefect`? `Effect.catchAllDefect(e => Effect.succeed(...))` on the whole exec? Use `Effect.sandbox`? Keep: wrap exec tool call body with `Effect.catchAllDefect`. Hmm, defects: `Effect.catchAllDefect` requires handler `(defect: unknown) => ...`. I'll apply at the call site in execTool for the tool.run portion: ```ts const outcome = yield* tool.run(input).pipe( Effect.timeoutOption(cfg.toolTimeout), // timeoutOption gives Option — success None => timed out ... ) ``` `Effect.timeoutOption` — exists? There's `Effect.timeoutOption` yes (v3). Returns `Effect, E, R>` — keeps original error type. Nice: then map None → failure string "timed out". Then `Effect.either` to fold errors. Let me write execTool carefully: ```ts const execTool = (step: number) => (call: ToolCall): Effect => Effect.gen(function* () { const started = yield* Clock.currentTimeMillis yield* publish({ _tag: "ToolStarted", step, call }) const result: { ok: boolean; body: unknown } = yield* runOne(call).pipe( Effect.either, Effect.map(either => Either.isLeft(either) ? { ok: false, body: String(either.left) } : { ok: true, body: either.right }) ) const ms = ... - started yield* publish({ _tag: "ToolFinished", step, call, ok: result.ok, ms }) return { role: "tool", toolCallId: call.id, content: JSON.stringify(result), isError: !result.ok } }).pipe(Effect.catchAllDefect(d => Effect.succeed(toolErrMessage(call, `defect: ${d}`)))) ``` But wait: unknown tool name — that's a failure inside runOne: ```ts const runOne = (call: ToolCall) => Effect.gen(function* () { const found = yield* registry.get(call.name) if (Option.isNone(found)) return yield* Effect.fail(new ToolNotFound({ name: call.name })) const tool = found.value const args = yield* decodeArgs(tool, call.arguments) return yield* tool.run(args).pipe(Effect.timeout(cfg.toolTimeout)) }) ``` Error channel: ToolNotFound | ParseError | TimeoutException | unknown(tool errors) — since tool.run error is `unknown`, union is unknown. OK. Then execTool maps any error into isError tool message — harness never crashes on tool failure. Agent result: ```ts export interface AgentResult { readonly goal: string readonly finalText: string readonly steps: number readonly transcript: ReadonlyArray } ``` Retry for LLM: policy in AgentLive: ```ts const retryPolicy = Schedule.exponential(Duration.seconds(0.2)).pipe( Schedule.intersect(Schedule.recurs(3)), Schedule.jittered ) ``` `Schedule.recurs` vs `Schedule.intersect` — in v3 `Schedule.recurs(n)` exists? v3 renamed to `Schedule.recurs` (was recurs in v2; v3 has `Schedule.recurs`). Yes v3: `Schedule.recurs`. Also `Schedule.jittered` exists. `Schedule.intersect` exists. Good. Simpler: `Schedule.exponential("200 millis", 2).pipe(Schedule.compose(Schedule.recurs(3)))`? intersect semantics fine. Also `Effect.retry(policy)` retries on all LlmError. OK. Now the Llm.complete requirement: Llm service only (no ToolEnv). Agent R: Llm | ToolRegistry | HarnessConfig | Events | ToolEnv(fs, http). Compose Layers: ```ts export const AgentLive = Layer.effect(Agent, Effect.gen(...)) // requires Llm, ToolRegistry, HarnessConfig, Events ``` Main: ```ts const AppLayers = Layer.mergeAll( ConfigLive, EventsLayer, MockOrOpenAi, // Llm ToolRegistryLayerWithBuiltins, NodeContext.layer, NodeHttpClient.layer ).pipe(Layer.provideMerge? ...) ``` Order: AgentLive needs the others: `AgentLive = AgentLive.pipe(Layer.provide([ConfigLive, EventsLayer, LlmLive, ToolsLive]))`. With mergeAll of all + AgentLive provided deps. Provide composition: ```ts const deps = Layer.mergeAll(ConfigLive, EventsLayer, LlmLive, ToolsLive, NodeContext.layer, NodeHttpClient.layer) const Full = Layer.provide(AgentLive, deps) ``` Wait Layer.provide(self, impl): `Layer.provide(AgentLive, deps)` gives layer requiring nothing. Yes. But careful: LlmLive = Layer.unwrapEffect(...) requires Config → deps include ConfigLive: order inside mergeAll irrelevant; deps merged must themselves be satisfied — ConfigLive no deps, LlmLive requires Config & HttpClient — since provided within same mergeAll, does Effect resolve? mergeAll builds layers in parallel; LlmLive's requirement of Config is satisfied only if Config is also provided *to* LlmLive — mergeAll doesn't cross-provide. Need explicit memo: ```ts const Base = Layer.mergeAll(ConfigLive, NodeContext.layer, NodeHttpClient.layer) // no requirements const LlmLive = Layer.provide(Layer.unwrapEffect(...), Base) const Tools = ToolRegistryLayer // builtins already; needs FileSystem/Http? registry itself just Ref; tools' deps appear in Agent's R not registry's const LlmAndBase = Layer.provideMerge(LlmLive, Base)? ``` Simpler: build in steps: ```ts const Platform = Layer.mergeAll(NodeContext.layer, NodeHttpClient.layer, ConfigLive) // provides platform + config const LlmLive = Layer.unwrapEffect(providerChoice) // requires Config const LlmProvided = Layer.provide(LlmLive, Platform) const All = Layer.provide(AgentLive, Layer.mergeAll(Platform, LlmProvided, EventsLayer, ToolsLayer)) ``` EventsLayer no deps; ToolsLayer no deps (Ref). AgentLive requires Llm, Registry, Config, Events + tool env (FileSystem, HttpClient, Clock...) which Platform provides. So All = Layer.provide(AgentLive, merge(Platform, LlmProvided, Events, Tools)). But careful: merging Platform (which provides Config etc.) and LlmProvided (provides Llm) fine — distinct tags. For the harness scenario runner, same composition but Mock script per scenario — build per scenario: ```ts const runScenario = (s: Scenario) => Effect.gen(function* () { const agent = yield* Agent const result = yield* agent.run(s.goal) return { name: s.name, pass: s.expect(result), result } }).pipe( Effect.provide(makeLayers(s.script)), Effect.catchAll(e => Effect.succeed({ name: s.name, pass: false, reason: renderError(e) })), Effect.withSpan("scenario", { attributes: { name: s.name } }) ) ``` makeLayers(script) similar composition as above with Mock.layer(script). Then `runAll` collects, prints table with `Effect.log`, returns failures count. exit code set. Main CLI mode: goal from argv; choose provider; run agent; stream events live; print final. Also subscribe to events: ```ts const printEvents = Effect.gen(function*(){ const events = yield* Events yield* events.subscribe.pipe? ``` If Events shape is PubSub directly: `const ps = yield* Events; yield* Stream.runForEach(Stream.fromQueue?? ...)`. Subscription from PubSub needs scope. In main I can wrap in `Effect.scoped`: ```ts const watch = Effect.gen(function* () { const pubsub = yield* Events yield* Stream.runForEach( Stream.unwrapScoped(Effect.map(PubSub.subscribe(pubsub), Stream.fromQueue)), e => Effect.log pretty ) }) // fork it const watcher = yield* Effect.forkDaemon(watch) // needs scope? subscribe needs Scope -> unwrapScoped provides ``` forkDaemon fine; but must interrupt at end: after run completes, `yield* Fiber.interrupt(watcher)`. Note: PubSub.publish when no subscribers — fine (bounded? unbounded pubsub always fine). Actually simpler: `Stream.fromPubSub`? Hmm, does `Stream.fromPubSub` exist in effect v3? I recall `Stream.fromPubSub(pubsub)` was added? There is `Stream.fromPubSub` ... I genuinely am unsure. There's `Stream.fromQueue` definitely (works for Subscription since Subscription extends Dequeue/Queue). And `PubSub.subscribe` returns `Effect, never, Scope>`. So `Stream.unwrapScoped(Effect.map(PubSub.subscribe(ps), Stream.fromQueue))` — solid. Use that. Hold on: is it `PubSub.subscribe: Effect, never, Scope>` — yes in v3. Also note `Stream.fromQueue` name — current: `Stream.fromQueue`. Yes. Now writing encodeMessage for OpenAI: ```ts const encodeMessage = (m: Message): unknown => { switch (m.role) { case "assistant": return { role: "assistant", content: m.content, tool_calls: m.toolCalls?.map(c => ({ id: c.id, type: "function", function: { name: c.name, arguments: typeof c.arguments === "string" ? c.arguments : JSON.stringify(c.arguments) } })) } case "tool": return { role: "tool", tool_call_id: m.toolCallId, content: m.content } default: return { role: m.role, content: m.content } } } ``` Also system prompt: agent prepends a system message describing harness ("You are... use tools..."). Configurable via config.systemPrompt default. Now, the loop termination check: completion.toolCalls empty → final. Some providers return both text and tool calls: we still run tools (text kept as assistant content). Handled. Max steps: `if (steps >= maxSteps)` fail StepLimitExceeded — but maybe nicer: force finalization? Fail is harness-y. Also catch: on failure at CLI, runMain prints error. For demo, catch and log. Also add `Effect.iterate` alternative? While loop in gen is fine and idiomatic (`Effect.gen` bodies can have while loops — yes, generators allow while with yield* inside). Memory: keep transcript in local array — plus show `Ref`? Local array + closure push is fine; but to show Ref usage... The registry uses Ref already. Fine. Add `Effect.annotateLogs`/spans: use `Effect.withSpan("agent.step", {attributes: {step}})`. And root: `Effect.withSpan("agent.run", { attributes: { goal } })`. Metrics: ```ts const steps = Metric.counter("agent_steps_total") const toolCalls = Metric.counter("agent_tool_calls_total") ... yield* Metric.increment(steps) ``` Metric.counter("name") returns Metric.Counter; increment. OK. Now the Mock streaming chunk: ```ts stream: (req) => Stream.unwrap(Effect.gen(function*(){ const step = peekNext(); const text = step._tag === "Text" ? step.text : ""; return Stream.make(...chunk(text)) })) ``` chunk by words. Keep simple: split into chunks of ~12 chars. Provider selection with Layer.unwrapEffect: ```ts export const LlmLive: Layer.Layer = Layer.unwrapEffect( Effect.gen(function* () { const provider = yield* Config.string("AGENT_PROVIDER").pipe(Config.withDefault("mock")) return provider === "openai" ? OpenAi.layer : Mock.layer(DEMO_SCRIPT) }) ) ``` Hmm OpenAi.layer requires HttpClient + Config; unwrapEffect preserves requirements. Then Layer.provide with platform. Good. Wait — one subtlety: `Layer.unwrapEffect` builds the layer once when layer is provided (memoized) — config read once. Good. Mock layer: script array; also expose `layerFor(script)`. The DEMO script for CLI mock mode: respond to any goal with a tool call to `clock.now`, then after seeing tool result, final text "The current time is ... (mock)". The mock can cheat by generating text referencing the tool result: since complete receives messages, mock can read last tool message content and include it! Nice: implement Mock as script of *planners*: `(messages) => MockStep`? Let me define MockStep as either canned `Completion` or a planner function. Simplest: two kinds: ```ts export type MockStep = | { readonly _tag: "Text"; readonly text: string } | { readonly _tag: "ToolCall"; readonly tool: string; readonly args?: unknown } | { readonly _tag: "EchoLastToolResult"; readonly prefix?: string } ``` EchoLastToolResult: looks back through messages for last tool message, returns final text prefix + content. That makes scenarios look real. Also idx increments only per complete() call — correct. Edge: concurrent scenarios each build their own Llm layer instance — separate Refs, no interference. Good since layer built per scenario. Now the harness CLI: `main` in package.json: `"dev": "tsx src/main.ts"`. Commands: `--demo` runs scenarios; otherwise goal string. Also include a tiny `README`-ish section in the answer explaining structure and how to run + what Effect features are showcased. The user asked to "prototype a complete agent harness" — deliverable is code. I'll present project tree, then each file's code, then run instructions and extension notes. Keep prose minimal but useful. Format thoughts: This is a code-heavy request; long code blocks expected. Use headers per file path, minimal commentary between. Provide package.json with pinned-ish versions (effect ^3.13, @effect/platform ^0.77? matching). Version pairing: effect 3.13 ↔ @effect/platform 0.77 / platform-node 0.82? The version matrices are fiddly; safer to give "latest" via npm install command: `npm i effect @effect/platform @effect/platform-node` and `npm i -D tsx typescript @types/node`. That avoids wrong pins. Good. tsconfig: ```json { "compilerOptions": { "target": "ES2022", "module": "NodeNext", // with tsx, "ESNext" also fine "moduleResolution": "NodeNext"? tsx handles; but type-check via tsc: use "Bundler"? } } ``` For tsx + tsc: use `"module": "ESNext"`, `"moduleResolution": "Bundler"`, `"strict": true`, `"verbatimModuleSyntax": true`? verbatim forces `import type` — our imports of interfaces (e.g., `import type { Message }`) — need care; skip verbatim. Set `"skipLibCheck": true`, `"exactOptionalPropertyTypes": false`. Fine. Now — potential API pitfalls to double check while writing: 1. `Context.Tag`: v3 pattern: ```ts export class Llm extends Context.Tag("harness/Llm")() {} ``` Yes. (Newer style `Context.Tag()` with explicit interface also exists; class style is fine and common.) 2. `Data.TaggedError("X")<{...}>` — yes. 3. `Effect.gen(function* () { ... })` with `yield*` — yes. 4. `Layer.effect(Tag, effect)` — yes. `Layer.effectSync(Tag, value)` — exists (sync). For Events: `Layer.effect(Events, PubSub.unbounded())` — PubSub.unbounded returns PubSub directly (not effect)? In v3: `PubSub.unbounded: () => PubSub `? I think it's `PubSub.unbounded (): PubSub ` — yes it's direct (was Effect in 3.0 alpha? no—`PubSub.unbounded` is plain). Hmm: In Effect v3, `PubSub.unbounded (): PubSub `. I recall usage: `yield* PubSub.unbounded()`? Let me think… `PubSub.bounded`, `PubSub.unbounded`, `PubSub.sliding`, `PubSub.dropping` — I believe these are all plain functions returning PubSub (not effects) in v3. Checking memory of source: `export const unbounded = (): PubSub => unsafeMake(UnboundedUnsafePublishAll...)`. Yes, plain. So `Layer.effectSync(Events, PubSub.unbounded())` or Layer.effect with Effect.succeed. Use `Layer.effectSync`. Hmm wait, actually I have doubt: in @effect/core v2 / effect v3, `Queue.unbounded` returns Effect? No—`Queue.unbounded (): Effect>`? I recall `Queue.unbounded` IS an Effect in v3 (`yield* Queue.unbounded()`). Yes Queue.unbounded returns Effect. And PubSub? `PubSub.unbounded` — I believe plain PubSub (the Effect-returning one is `PubSub.bounded`? no...). Ugh. Let me recall docs: From effect docs (PubSub module): ```ts const pubsub = yield* PubSub.bounded(10) ``` and unbounded: `const pubsub = yield* PubSub.unbounded()`? I think both are Effects in v3. Actually yes — I'm now fairly convinced `PubSub.unbounded` returns `Effect>` in v3 (they made all constructors Effect for consistency? but `Semaphore`...). Hmm. To dodge: use `Effect.sync(() => PubSub.unbounded())`? If PubSub.unbounded returns Effect, then Effect.sync wrapping it gives Effect> — wrong. Safe approach: `Layer.effect(Events, PubSub.unbounded())` — if unbounded is plain, this is wrong type (needs Effect). If it's Effect, this works. If plain, use Effect.succeed(PubSub.unbounded()). Resolve: I'm going to check both possibilities... From the actual effect repo (packages/effect/src/PubSub.ts), v3: ```ts export const bounded = (capacity: number): Effect> => ... export const unbounded = (): Effect> => ... ``` I do recall `PubSub.unbounded` having an Effect return in v3 — yes, because it uses `unsafeMake` internally and the public API is effectful to allow future backpressure semantics. I'm ~85% confident: In effect v3, `PubSub.unbounded ()` returns `Effect>`. There's also `PubSub.unsafeMake`. OK go with `Layer.effect(Events, PubSub.unbounded())`? Wait — if I'm wrong and it's plain, type error for user. Hmm. Mitigation: use `Effect.suspend`/gen: `Layer.effect(Events, Effect.gen(function*(){ return yield* PubSub.unbounded() }))` — if it's plain function, `yield*` on non-Effect is type error too. Alternative: skip PubSub; use `SynchronizedRef`/Queue of events? Queue.unbounded is definitely Effect in v3 (`yield* Queue.unbounded()` — yes I'm certain Queue constructors are effects). Use an unbounded Queue as the event bus with `Stream.fromQueue(queue)` (Stream.fromQueue works with Queue directly, and repeated subscribers? A Queue is single-consumer; PubSub is multi. For CLI demo one consumer + maybe none else — but harness also might collect. With one consumer per process, Queue fine. But scenarios run concurrently in same runtime sharing one Events queue → mixing events across scenarios. If harness doesn't subscribe, only CLI subscribes. Acceptable: events bus for CLI display. But scenario runs with forEach concurrency would interleave events into the queue — only consumed in CLI mode; in demo mode we ignore queue contents (unbounded memory — fine for demo) or provide fresh Events per scenario. Each scenario builds its own layers → own Events queue. Good: per-scenario layer composition anyway. So: `Events` Tag holding `Queue.Queue`. publish = `Queue.offer(queue, e)` (void). subscribe stream = `Stream.fromQueue(queue)` — but queue single-consumer... CLI takes all. OK. Hmm, but multi-subscriber is nicer conceptually. Alternative: use `Stream.fromSchedule`? no. Keep Queue, note in comment that PubSub enables multiple subscribers. Actually wait — I can have Events service expose `subscribe` implemented via PubSub if I construct PubSub inside Layer.effect with gen (yield*). If `PubSub.unbounded` is Effect → `yield* PubSub.unbounded()` compiles. If plain → compiles too? `yield* plainValue` — generator yield* requires iterable/Effect-like; PubSub isn't — type error. So gen approach doesn't dodge. Decision: use Queue (certain API) — `Layer.effect(Events, Effect.map(Queue.unbounded(), q => ({ offer..., events: Stream.fromQueue(q) })))`? Wait but Stream.fromQueue(q) consumes — CLI only. And in AgentLive, publish via service shape `{ publish: (e) => Effect }`. Simple service shape: ```ts export class Events extends Context.Tag("harness/Events") Effect readonly subscribe: Stream // lazily consumed once }>() {} ``` Hmm Stream as data — fine. But if harness scenarios + CLI both... whatever, prototype. Actually — simpler and unimpeachable: skip the Events service; agent logs via `Effect.log` (built-in structured logger) with spans/annotations, and CLI streaming is only about *LLM text streaming* (which needs provider stream anyway). Drop PubSub entirely; keep `Llm.stream` for token streaming in CLI mode with OpenAI/Mock. That reduces API risk and code size. The "event stream" idea is cool but risky APIs; structured logs demonstrate observability. Also `Effect.tap` with logs. But showing PubSub/Stream in the harness is a big "effect native" flex the user likely wants ("complete agent harness", "effect native"). Middle ground: include streaming LLM output in CLI via `Llm.stream` when final answer... but agent uses complete; CLI can't easily stream mid-loop. Could implement agent's final step with streaming when available... complexity. Alternative showcase for Stream: `Stream.fromSchedule` ticker fiber in CLI showing elapsed time — tiny, uses Schedule + fork + interrupt. Include that (small). And Stream for SSE in OpenAI provider — but CLI mode uses complete(); SSE code unused unless... make CLI use `stream` and agent...? No — keep agent on complete. SSE code present but unused = dead code smell. Hmm. Option: agent uses streaming internally: complete implemented in terms of stream + accumulation in providers (OpenAi.complete = collect SSE then aggregate). That kills two birds: OpenAI implements `stream` as primitive (SSE), and `complete` = `stream |> accumulate into Completion (buffering deltas, capturing tool_calls, finish_reason, usage)`. That's realistic (many harnesses do exactly this) and demonstrates Stream.reduce / transducers. Mock: complete primitive; stream = chunk text. Agent uses complete. Implementing complete-from-stream in OpenAI: ```ts const complete = (req) => streamSse(http, cfg, req, { stream: true }).pipe( Stream.mapAccum(initialAcc, (acc, delta) => applyDelta(acc, delta)), Stream.runLast? ``` Deltas include content, tool_calls (with index/id/function name/args fragments), finish_reason. Accumulate: concat content; tool call fragments merged by index (concat arguments). Then final Completion. Doable but adds ~50 lines of fragile parsing (tool call delta merging). For a prototype demo, acceptable risk? The Mock path (default, runs without keys) is the primary demo; OpenAI path should compile. Delta merging logic is provider-specific detail — I'll implement it but keep it tolerant (unknown fields → skip via catch in parse). Simpler alternative: OpenAI complete = plain non-streaming POST JSON (as earlier), and stream method also provided (SSE) used by nobody? Dead code. OR omit stream from service entirely and note extension. Hmm. Given "prototype completeness", I'll include both complete (non-stream) and stream (SSE) in the OpenAI provider, and in CLI mode with provider=openai, the agent still uses complete; the `stream` is there for future use — acceptable, and I'll note it. Actually wait — I can have CLI print tool events + final text; streaming tokens only matters interactively. Fine: leave stream implemented (used by `--watch`? no). It's fine — a complete harness API would have it; prototype shows the wiring. Hmm, actually, let me reconsider: maybe use the streaming path for the final assistant message only... no. Moving on. One more piece: Redacted usage: `Config.redacted("OPENAI_API_KEY")` → `Config`; wrap option: `Config.option(Config.redacted("OPENAI_API_KEY"))` → Config>. In provider: `Option.isSome(key) ? HttpClientRequest.bearerToken(Redacted.value(key.value)) : (a) => a` — Redacted.value(redacted) returns string. Yes: `Redacted.value: (self) => string`. Pipe identity: use `Function.identity` or just conditional spread: build request in gen with if/else — clearer than piping identity: ```ts const base = HttpClientRequest.post(`${cfg.baseUrl}/chat/completions`).pipe(HttpClientRequest.bodyUnsafe("application/json", payload)) const req = Option.isSome(cfg.apiKey) ? HttpClientRequest.bearerToken(Redacted.value(cfg.apiKey.value))(base) : base ``` `HttpClientRequest.bearerToken(token)` returns `(self: HttpClientRequest) => HttpClientRequest`? The combinators are dual: `HttpClientRequest.bearerToken: (token: string) => (self) => HttpClientRequest`? Hmm — HttpClientRequest combinators like `HttpClientRequest.setHeader(name, value)` have signature `(self: HttpClientRequest) => HttpClientRequest` with pipe-friendly... Actually they're defined as functions taking request last? Usage `HttpClientRequest.post(url).pipe(HttpClientRequest.setHeader("a","b"))` implies setHeader: (name, value) => (self) => req. Yes, curried data-last for pipe. So `bearerToken(Redacted.value(k))(base)` works. `bodyUnsafe(contentType, content)` data-last similarly: `HttpClientRequest.bodyUnsafe("application/json", payload)` as combinator in pipe. Signature I recall: `bodyUnsafe: (contentType: string, content: string | ArrayBuffer | Uint8Array) => (self) => HttpClientRequest`. Hmm or `(body: Body)`. There's also `HttpClientRequest.body`? I'll go with bodyUnsafe — I'm fairly confident it exists in @effect/platform HttpClientRequest (used commonly: `HttpClientRequest.bodyUnsafe("application/json", JSON.stringify(x))`). Yes I've seen that exact usage. Timeout on http.execute? `res` effect: add `Effect.timeout` in caller? Llm error mapping: wrap: ```ts const res = yield* http.execute(req).pipe(Effect.timeoutFail({ duration: cfg.requestTimeout, onTimeout: () => new LlmError({reason: "request timeout"}) })) ``` `Effect.timeoutFail` exists (v3). ok. res.text: `HttpClientResponse.text(res)` or method `res.text` — response has `.text: Effect` property? In @effect/platform, HttpClientResponse has methods like `res.json`, `res.text` as Effect-valued properties? I recall `const json = yield* response.json`. Yes — `response.json: Effect`, `.text` similarly. Good. Status filter: there's `HttpClientResponse.filterStatusOk(res)`? I recall `HttpClientResponse.filterStatusOk` exists: `(self) => Effect`. In newer versions moved to HttpClient: `HttpClient.filterStatusOk` operates on Effect. To be safe, manual status check — doing manual check anyway for error body. Good. FileSystem readFile returns `Uint8Array` in newer versions (Buffer earlier). Decode: `new TextDecoder().decode(bytes)`. Both fine with TextDecoder(Buffer works too). Clock: `Clock.currentTimeMillis: Effect` — yes (Clock.currentTimeMillis is an effect property? `yield* Clock.currentTimeMillis` — it's `Clock.currentTimeMillis: Effect` — yes as effect constant). `Schedule.exponential(Duration.seconds(0.2), 2.0)`? Signature: `exponential(base: Duration, factor?: number)`. ok. `Schedule.jittered` combinator: `Schedule.jittered(schedule)`. ok. `Schedule.recurs(3)`. intersect: `Schedule.intersect(self, that)` or pipe. Use: ```ts const llmRetry = Schedule.exponential(Duration.millis(200), 2).pipe( Schedule.intersect(Schedule.recurs(3)), Schedule.jittered ) ``` `Effect.retry(policy)`. Metric: `Metric.counter("agent.steps")` → Counter; `Metric.increment(counter)` effect. Also gauge for in-flight? skip. Now `Effect.iterate`? I'll use while loop in gen — legal since gen is a generator; but mutation + while inside generator is fine. But there's a subtlety: `while (true) { ... return ... }` with yield* inside — allowed. TS narrowing fine. Alternatively recursive with Effect.suspend. While-loop reads better; keep while. Also demonstrate `Ref` in agent for messages? I'll use plain array (closure) — fine, plus Ref in registry & mock. Also demonstrate `Effect.forEach` concurrency and `Effect.all` with `discard`. Also demonstrate `Exit`/`Either` where natural (tool error folding via Effect.either + Either.isLeft — good; import { Either }). Also demonstrate `Option` (registry get, config key). Also demonstrate `Match`? Could use for encodeMessage; adds import; maybe skip to reduce noise. Use plain switch. Also demonstrate custom `Logger`? Use built-in `Effect.logInfo`/`Effect.logDebug` with `Effect.annotateLogs({ step })`. In CLI, set logger level via `Logger.minimumLogLevel`? Provide `Logger.pretty` default in NodeRuntime — runMain uses pretty logger by default. Add `Effect.withLogSpan`? We have spans via withSpan — the built-in logger shows span timings if using `Effect.log` within span? Pretty logger displays spans when effect completes? Not exactly; keep spans for FiberRuntime/tracing and mention `Effect.withTracingEnabled`. Keep simple. CLI output: use `Console.log` via `Effect.logInfo` — pretty-printed with the default logger. For final answer printing, maybe raw `Console.log` for clean text. Use `Console.log` (Effect-native via `Console` service: `yield* Console.log(...)` — Console module in effect: `import { Console } from "effect"` and `Console.log: (...args) => Effect`. Yes.) Now, watcher fiber interrupting: after agent completes, `yield* Fiber.interrupt(watcherFiber)`. But subscribe stream from queue is infinite — runForEach never ends. Interrupting fiber: fine. Use `Effect.forkDaemon`? Within runMain, no scope around main? NodeRuntime.runMain runs with a scope? runFork creates runtime... `Effect.forkDaemon` returns fiber not tied to scope; interrupt manually. OK. But wait: watch uses Events.subscribe which is Stream.fromQueue(queue) — if CLI mode only, and stream consumed once. Note in code comment. Actually, simpler for CLI: instead of watch fiber, just `Effect.tap` log per event via... no, events happen inside agent.run; tap wrapper: run agent with events → we can wrap: `agent.run(goal)` publishes to queue; watcher consumes. Fork watcher first, run agent, then interrupt watcher. Include it — demonstrates fibers & Stream. Potential issue: `Stream.fromQueue(queue)` ends never; `Stream.runForEach` → Effect never completes until interrupt. forkDaemon + later interrupt works. Now Scenarios for --demo. Define 3: 1. "tool round-trip": goal "What time is it? Use the clock tool." script: [ToolCall clock.now, EchoLastToolResult "Current time: "] expect: finalText includes "Current time:" && steps === 2. Actually EchoLastToolResult prefix "Current time: " plus tool content (ISO string JSON-quoted? tool content is JSON.stringify({ok:true, body: "..."})) — echo includes full JSON — ugly but fine; mock can slice. Keep expect: includes "20" whatever — better expect: steps === 2 && finalText.length > 0 && transcript contains tool message. Let me make expect functions pragmatic. 2. "unknown tool recovery": script: [ToolCall "does_not_exist", EchoLastToolResult "Recovered: "] expect finalText includes "Recovered". Demonstrates error-as-result path. 3. "step limit": script: 5× ToolCall echo...; config maxSteps maybe 3 → expect failure StepLimitExceeded. Scenario result type must accommodate failure: runScenario catches error into { failed: true, error }. Expect can be `outcome: "failure"`? Define Scenario.expect as `(outcome: Outcome) => boolean` where Outcome = { _tag:"Success", result } | { _tag:"Failure", error: unknown }? Simplify: expectSuccess?: (r) => boolean OR expectError?: (e: unknown) => boolean. I'll give each scenario an `expect: (r: ScenarioOutcome) => boolean`. Implement runScenario building layers per scenario: ```ts const layersFor = (script) => { const platform = Layer.mergeAll(ConfigLive, NodeContext.layer, NodeHttpClient.layer) return Layer.provide(AgentLive, Layer.mergeAll(platform, Mock.layer(script), ToolsLayer, EventsLayer?...)) ``` Wait — Events dropped? Decide: I said keep Events service with Queue? I earlier waffled. Let me finalize: Include `Events` service backed by unbounded Queue; AgentLive publishes; CLI watches. Harness scenarios don't watch. This shows Queue + Stream.fromQueue + fiber lifecycle. Cost: ~25 lines. OK include. Hmm, but per-scenario layer builds new Events queue — no cross-talk. Good. Also — AgentLive R: Llm | ToolRegistry | Events | HarnessConfig | FileSystem | HttpClient | (Clock default) | (Logger default). Note: tools' run deps: FileSystem & HttpClient — typed as ToolDeps = FileSystem | HttpClient. Agent's R must include ToolDeps. When AgentLive is created via Layer.effect(Agent, gen(...)), the effect's R includes those; Layer carries requirement. Provide NodeContext.layer (FileSystem+Path+...) and NodeHttpClient.layer. Clock: default Clock is in any runtime — built-in, no requirement. Good. One risk: `FileSystem` tag import from "@effect/platform" (FileSystem.FileSystem service interface). Type: `FileSystem.FileSystem`. HttpClient type: `HttpClient.HttpClient` (the Tag itself is the type? In v3: `HttpClient` is a Tag; using as type: `HttpClient.HttpClient`? The Tag is `HttpClient` (class) and service type interface `HttpClient.HttpClient`? Hmm. In @effect/platform v3, `HttpClient` exported as `class HttpClient extends Context.Tag(...)`, and usage: `yield* HttpClient` gives `HttpClient` service? With new Tag style, the service interface is the class's static type: `Context.Tag` where Shape is declared in class generic... For @effect/platform HttpClient: declared as: ```ts export class HttpClient extends Context.Tag(".../HttpClient")() {} ``` Hmm, not exactly; I recall `HttpClient.Service` interface exists and `HttpClient` tag; you can reference type via `HttpClient.Service`. Similarly `FileSystem.Service`? FileSystem: `export class FileSystem extends Context.Tag(...)()`. Hmm, older platform had `FileSystem` as a Tag with `FileSystem.Service`. Actually I recall `FileSystem.FileSystem` — older versions: `export interface FileSystem` + `export const FileSystem: Tag`. Newer: class-based with `Service` namespace. To dodge type-annotation needs, I don't need to name these types at all if I write tool run handlers with Effect.gen and yield* the Tags — inference handles it. Tool run type: `(input: I) => Effect` where `type ToolDeps = FileSystem | HttpClient`? Need those type names... If class-based, `ToolDeps = FileSystem | HttpClient` works if the class names are usable as types (Context.Tag classes: the class itself is both Tag & type of service? With `class HttpClient extends Context.Tag(id)()`, the class HttpClient as a type refers to... the instance type of the class which is `Service`? Actually pattern: `Context.Tag()` — first type param is the *tag identifier type* used contextually; the class instance type equals Service shape? Hmm: In v3 class-based Tags: `class Foo extends Context.Tag("Foo")()` — `Foo` used as type refers to Shape? Yes — the magic: the class is declared such that `Foo` (type) = Shape (the service). Because Context.Tag's prototype declares `Type` phantom... The idiomatic usage: `const foo: Foo = yield* Foo`. Yes, that's the standard v3 pattern — the class name serves as the service type. So `ToolDeps = FileSystem.FileSystem | HttpClient`? For platform, I believe current declarations are like: ```ts export class FileSystem extends Context.Tag("effect/FileSystem")() {} export namespace FileSystem { export interface Service {...} } ``` So type usage: `FileSystem` (the class as type) = Service. And older code wrote `FileSystem.FileSystem`. With class-style, `FileSystem` as type works. HttpClient: `export class HttpClient extends ... ()`. So `HttpClient` as type = service. OK so `type ToolDeps = FileSystem | HttpClient` referencing imported classes as types — good, no property access gymnastics. Since I import them for `yield*` anyway. Wait, careful: In @effect/platform current (v3.x), is FileSystem class-style? I believe yes since ~0.60+ they migrated tags to class style. Fine. `Path` needed? For fs tool path join? skip. Now AgentLive R listing: Llm, ToolRegistry, HarnessConfig, Events, FileSystem, HttpClient. Its Layer requires those; final provide merges platform layers. Let me also double-check `Layer.mergeAll(ConfigLive, NodeContext.layer, NodeHttpClient.layer)` — NodeContext.layer type: provides many services; mergeAll unions. NodeHttpClient.layer requires... nothing (or Clock). ok. Then `Layer.provide(LlmLive, Platform)` where LlmLive requires Config + HttpClient (both in Platform). But LlmLive (unwrapEffect) requires Config (reads provider) and its returned layer (OpenAi.layer) requires HttpClient+Config; unwrapEffect combines requirements = Config + HttpClient + Config → Config & HttpClient. Provide Platform satisfies. Resulting Layer. Then final: `Layer.provide(AgentLive, mergeAll(Platform, LlmProvided, ToolsLayer, EventsLayer))` — AgentLive requires Llm, Registry, Config, Events, FileSystem, HttpClient → all present. But careful: Platform included twice (directly and within LlmProvided) — memoization: Layer.provide(LlmLive, Platform) uses same Platform instance; Effect layers memoize per reference — same reference shared, no duplicate build. Good, that's a nice note (memoization by reference). Simpler composition in code: ```ts const PlatformLayer = Layer.mergeAll(ConfigLive, NodeContext.layer, NodeHttpClient.layer) const LlmLayer = Layer.provide(LlmLive, PlatformLayer) const FullLayer = Layer.provide(AgentLive, Layer.mergeAll(PlatformLayer, LlmLayer, ToolsLayer, EventsLayer)) ``` ToolsLayer = registry preloaded with builtins: `ToolRegistry.layerWith(builtins)` where layerWith = Layer.effect(ToolRegistry, make(tools)). Requires nothing. EventsLayer = Layer.effect(Events, Queue-based shape). Now `HarnessConfig` — but wait, ConfigLive uses Effect's `Config` module reading env: `Config.integer("AGENT_MAX_STEPS")` — Config.integer exists? v3 Config: `Config.integer`? There's `Config.number`, `Config.integer`... I recall `Config.integer` exists. Yes. `Config.duration("AGENT_TOOL_TIMEOUT")` — Config.duration exists → Config. ConfigLive: ```ts export class HarnessConfig extends Context.Tag("harness/Config")() {} export const ConfigLive = Layer.effect(HarnessConfig, Effect.gen(function* () { const maxSteps = yield* Config.integer("AGENT_MAX_STEPS").pipe(Config.withDefault(8)) ... return { maxSteps, ... } })) ``` Fields: maxSteps, toolConcurrency (default 4), toolTimeout (Duration seconds 10), requestTimeout (30s), systemPrompt (default string), model, baseUrl, apiKey (Option). Provide defaults via `Config.withDefault`. Also `Config.string("AGENT_MODEL").pipe(Config.withDefault("gpt-4o-mini"))`. Note: For mock-only demo, env vars absent → defaults used. `Config.option(Config.redacted("OPENAI_API_KEY"))` with option → no failure when missing. Good. Now Agent file. Let me write full code mentally with types: ```ts import { Clock, Config, Context, Data, Duration, Effect, Layer, Metric, Option, Redacted, Schedule } from "effect" ``` Domain.ts: ```ts export type Role = "system" | "user" | "assistant" | "tool" export interface ToolCall { readonly id: string; readonly name: string; readonly arguments: unknown } export type Message = | { readonly role: "system"; readonly content: string } | { readonly role: "user"; readonly content: string } | { readonly role: "assistant"; readonly content: string; readonly toolCalls: ReadonlyArray } | { readonly role: "tool"; readonly toolCallId: string; readonly content: string; readonly isError: boolean } export interface ChatRequest { readonly messages: ReadonlyArray readonly tools: ReadonlyArray readonly temperature?: number } export interface ToolSpec { readonly name: string; readonly description: string; readonly parametersJsonSchema: unknown } export interface Usage { readonly promptTokens: number; readonly completionTokens: number } export interface Completion { readonly text: string readonly toolCalls: ReadonlyArray readonly finishReason: string readonly usage: Option? // Option in data — meh; use usage?: Usage } ``` Keep `usage?: Usage`. Errors.ts: ```ts import { Data } from "effect" export class LlmError extends Data.TaggedError("LlmError")<{ readonly reason: string; readonly status?: number }> {} export class StepLimitExceeded extends Data.TaggedError("StepLimitExceeded")<{ readonly maxSteps: number }> {} export class ToolNotFound extends Data.TaggedError("ToolNotFound")<{ readonly name: string }> {} export class InvalidToolArgs extends Data.TaggedError("InvalidToolArgs")<{ readonly name: string; readonly detail: string }> {} ``` Tools.ts: ```ts import { Context, Effect, Layer, Option, Ref, Schema, JSONSchema } from "effect" import { FileSystem, HttpClient, HttpClientRequest } from "@effect/platform" import type { ToolSpec } from "./Domain.js" import { ToolNotFound, InvalidToolArgs } from "./Errors.js" export interface ToolDeps {} // widened by imports export interface Tool { readonly name: string readonly description: string readonly parameters: Schema.Schema readonly run: (input: I) => Effect.Effect } ``` Hmm — run R: FileSystem | HttpClient for all tools even if unused; widening ok. But `Effect` — a tool that needs nothing still assignable (R covariant). Good. Tool.Any = Tool. Registry service: ```ts export class ToolRegistry extends Context.Tag("harness/ToolRegistry") Effect> readonly specs: Effect> }>() {} export const makeRegistry = (tools: ReadonlyArray) => Layer.effect(ToolRegistry, Effect.gen(function* () { const map = yield* Ref.make(new Map(tools.map(t => [t.name, t]))) const get = (name: string) => Effect.map(Ref.get(map), m => Option.fromNullable(m.get(name))) const specs = Effect.map(Ref.get(map), m => Array.from(m.values()).map(t => ({ name: t.name, description: t.description, parametersJsonSchema: JSONSchema.fromSchema(t.parameters) }))) return { get, specs } })) ``` JSONSchema.fromSchema returns `JSONSchema` — assign to unknown field fine. Builtins: ```ts const MAX_BYTES = 8192 export const echo: Tool<{ message: string }> = { name: "echo", description: "Echo a message back. Useful for testing.", parameters: Schema.Struct({ message: Schema.String }), run: (i) => Effect.succeed(i.message) } export const now: Tool<{}> = { name: "clock.now", description: "Current wall-clock time in ISO-8601 (UTC).", parameters: Schema.Struct({}), run: () => Effect.map(Clock.currentTimeMillis, (ms) => new Date(ms).toISOString()) } ``` Schema.Struct({}) — empty struct; decodeUnknown of {} from JSON "{}" ok. fs.read: ```ts export const readFile: Tool<{ path: string }> = { name: "fs.readFile", description: "Read a UTF-8 text file (first 8KB).", parameters: Schema.Struct({ path: Schema.String }), run: ({ path }) => Effect.gen(function* () { const fs = yield* FileSystem const bytes = yield* fs.readFile(path) return new TextDecoder().decode(bytes).slice(0, MAX_BYTES) }) } ``` fs.readFile error type: platform FileError — assignable to unknown error channel. http.getText: ```ts export const httpGet: Tool<{ url: string }> = { name: "http.getText", description: "GET a URL, return first 8KB of the body as text.", parameters: Schema.Struct({ url: Schema.String }), run: ({ url }) => Effect.gen(function* () { const http = yield* HttpClient const res = yield* http.execute(HttpClientRequest.get(url)) const body = yield* res.text return body.slice(0, MAX_BYTES) }) } ``` `http.execute(request)` — signature: `execute: (request) => Effect`? In newer versions, `HttpClient.execute` returns `Effect`? Response streaming needs scope; but for `.text` (full body read), the client wraps... I recall `client.execute(req)` returns `Effect` where response body is consumed via methods; and there's `Effect.scoped` wrapping concerns. In current @effect/platform, `HttpClient.execute` returns `Effect`? Hmm. There was a change: responses are scoped; helpers `client.get(url)`... Let me think about how docs show it: ```ts const program = Effect.gen(function* () { const client = yield* HttpClient const response = yield* client.get("https://jsonplaceholder.typicode.com/todos/1") const json = yield* response.json }) ``` `client.get` exists and handles scope (I believe `get`/`post` helpers internally scoped). For `execute`, I think signature: `execute(request: HttpClientRequest): Effect` — response requires scope because stream. But `.text` consumes... still needs the scope alive during consumption. To be safe: wrap in `Effect.scoped`: ```ts const body = yield* (Effect.gen(function* () { const res = yield* http.execute(HttpClientRequest.get(url)) return yield* res.text })).pipe(Effect.scoped) ``` Hmm wait — is `Scope` in the R channel or E? Scope is R (context). `Effect.scoped` provides it. If execute doesn't need Scope, Effect.scoped harmless. But if res.text must be inside scope — with Effect.scoped wrapping the gen, yes. OK use Effect.scoped wrapper. Actually simpler: `http.get(url)` convenience exists? I believe `HttpClient` service has `get`, `post`, `execute`... The `HttpClient` interface: `execute`, plus `get`, `post` helpers? I recall service has `.execute` and convenience `.get(url: string)` returning Effect (scoped?). Not sure about `.get` — I'll use execute + scoped. Safe. For OpenAI provider same pattern. Llm.ts: ```ts import { Context, Data, Effect, Layer, Stream } from "effect" import type { ChatRequest, Completion } from "./Domain.js" export class LlmError extends Data.TaggedError("LlmError")<{ readonly reason: string; readonly status?: number }> {} export class Llm extends Context.Tag("harness/Llm") Effect readonly stream: (req: ChatRequest) => Stream.Stream }>() {} ``` Wait Errors.ts already has LlmError; keep LlmError in Llm.ts to colocate. Drop Errors.ts LlmError. Actually keep a single Errors.ts for all — fine either way. I'll colocate: Domain, then Llm includes LlmError; Tools includes tool errors; Agent includes StepLimitExceeded. Reduces file count. Mock.ts: ```ts import { Effect, Layer, Ref, Stream } from "effect" import { Llm } from "../Llm.js" import type { Completion, Message } from "../Domain.js" export type MockStep = | { readonly _tag: "Text"; readonly text: string } | { readonly _tag: "ToolCall"; readonly tool: string; readonly args?: unknown } const findLastToolContent = (messages: ReadonlyArray): string => {...} export const layer = (script: ReadonlyArray) => Layer.effect(Llm, Effect.gen(function* () { const i = yield* Ref.make(0) return { complete: (req) => Effect.gen(function* () { const n = yield* Ref.getAndUpdate(i, (n) => n + 1) const step = script[n] if (step === undefined) { return { text: "Mock LLM: script exhausted.", toolCalls: [], finishReason: "stop" } } if (step._tag === "Text") return { text: step.text, toolCalls: [], finishReason: "stop" } // ToolCall step: if EchoLastToolResult-like... }), stream: (req) => Stream.empty } })) ``` Hmm the "EchoLastToolResult" variant — I planned 3 step kinds. Let me define MockStep ToolCall returns tool call with generated id `call_${n}`; and a separate step kind "SummarizeLastTool" that scans messages for last role==="tool" and returns its content as text. Good: ```ts | { readonly _tag: "RepeatToolResult"; readonly prefix?: string } ``` complete for that: look at req.messages reversed find role tool → content; return text = (prefix ?? "") + content. stream: chunk the text that complete would return? Implement stream via same logic: `Stream.unwrap(Effect.map(nextText, t => Stream.make(...chunks(t))))` — need factor out `nextCompletion: Effect` used by both. stream then splits completion.text into ~16-char pieces, ignoring toolCalls (stream only final text). fine. Default demo script for CLI mock mode: ```ts export const demoScript: ReadonlyArray = [ { _tag: "ToolCall", tool: "clock.now", args: {} }, { _tag: "RepeatToolResult", prefix: "Mock summary → " } ] ``` OpenAi.ts: write carefully. ```ts import { Config, Duration, Effect, Layer, Option, Redacted, Schedule, Schema, Stream } from "effect" import { HttpClient, HttpClientRequest } from "@effect/platform" import { HarnessConfig } from "../Config.js" import { Llm, LlmError } from "../Llm.js" import type { ChatRequest, Completion, Message } from "../Domain.js" const ApiMessage = Schema.Struct({ role: Schema.String, content: Schema.NullOr(Schema.String), tool_calls: Schema.optional(Schema.Array(Schema.Struct({ id: Schema.String, function: Schema.Struct({ name: Schema.String, arguments: Schema.String }) }))) }) const ApiResponse = Schema.Struct({ choices: Schema.Array(Schema.Struct({ finish_reason: Schema.optional(Schema.String), message: ApiMessage })), usage: Schema.optional(Schema.Struct({ prompt_tokens: Schema.Number, completion_tokens: Schema.Number })) }) const decodeResponse = Schema.decodeUnknown(Schema.parseJson(ApiResponse)) export const layer = Layer.effect(Llm, Effect.gen(function* () { const cfg = yield* HarnessConfig const http = yield* HttpClient const endpoint = `${cfg.baseUrl}/chat/completions` const authorize = (r: HttpClientRequest): HttpClientRequest => Option.isSome(cfg.apiKey) ? HttpClientRequest.bearerToken(Redacted.value(cfg.apiKey.value))(r) : r ``` Need import Redacted from "effect". encodeMessage + encodeTool as planned. bodyOf: ```ts const bodyOf = (req: ChatRequest, stream: boolean) => ({ model: cfg.model, temperature: 0.2, stream, messages: req.messages.map(encodeMessage), tools: req.tools.length > 0 ? req.tools.map(t => ({ type: "function", function: { name: t.name, description: t.description, parameters: t.parametersJsonSchema } })) : undefined }) ``` undefined tools field — JSON.stringify drops undefined — fine. complete: ```ts const complete = (req: ChatRequest): Effect => Effect.gen(function* () { const payload = JSON.stringify(bodyOf(req, false)) const request = authorize(HttpClientRequest.post(endpoint).pipe(HttpClientRequest.bodyUnsafe("application/json", payload))) const response = yield* http.execute(request).pipe( Effect.timeoutFail({ duration: cfg.requestTimeout, onTimeout: () => new LlmError({ reason: `timeout after ${Duration.format(cfg.requestTimeout)}` }) }) ) const text = yield* response.text if (response.status >= 400) return yield* Effect.fail(new LlmError({ reason: text.slice(0, 400), status: response.status })) const decoded = yield* Effect.mapError(decodeResponse(text), (e) => new LlmError({ reason: `bad response: ${e.message}` })) // ParseError has message const choice = decoded.choices[0] if (choice === undefined) return yield* Effect.fail(new LlmError({ reason: "empty choices" })) return { text: choice.message.content ?? "", toolCalls: (choice.message.tool_calls ?? []).map(c => ({ id: c.id, name: c.function.name, arguments: c.function.arguments })), finishReason: choice.finish_reason ?? "stop", usage: decoded.usage && { promptTokens: decoded.usage.prompt_tokens, completionTokens: decoded.usage.completion_tokens } // careful && yields undefined|obj ok } }).pipe(Effect.mapError?...) ``` Hmm error channel: http.execute errors are HttpClientError; response.text errors ResponseError; decode ParseError. I want all → LlmError. Wrap: `Effect.mapError` won't merge multi sources cleanly; use `Effect.catchAll` at end? Simplest: at the end of gen pipe: `.pipe(Effect.catchAll((e) => Effect.fail(e instanceof LlmError ? e : new LlmError({ reason: renderError(e) }))))`. renderError: `String(e)`? For Error: `String(e)` gives "Error: msg"? For tagged Data errors, includes message. Use a helper: ```ts const render = (e: unknown) => e instanceof Error ? e.message : String(e) ``` Fine. But careful: `Effect.timeoutFail` on http.execute: timeoutFail wraps effect erroring TimeoutException→LlmError, but underlying HttpClientError still LlmError needed. The outer catchAll normalizes. Good. Also `Effect.timeoutFail` requires onTimeout returning error of same channel — ok. Note `Effect.timeoutFail` signature: `Effect.timeoutFail({ duration, onTimeout })` — data-last pipeable, yes: `Effect.timeoutFail({ duration: Duration.seconds(30), onTimeout: () => new XError(...) })`. stream via SSE: ```ts const stream = (req: ChatRequest): Stream.Stream => Stream.unwrap(Effect.sync(() => { const payload = JSON.stringify(bodyOf(req, true)) const request = authorize(HttpClientRequest.post(endpoint).pipe(HttpClientRequest.bodyUnsafe("application/json", payload))) return http.execute(request).pipe( Effect.map((res) => res.stream), Stream.unwrapEffect, Stream.decodeText(), Stream.splitLines, Stream.filterMap((line) => { const trimmed = line.trim() if (!trimmed.startsWith("data:")) return Option.none() const data = trimmed.slice(5).trim() if (data === "" || data === "[DONE]") return Option.none() try { const chunk = JSON.parse(data) const delta = chunk?.choices?.[0]?.delta?.content return typeof delta === "string" && delta.length > 0 ? Option.some(delta) : Option.none() } catch { return Option.none() } }), Stream.mapError((e) => new LlmError({ reason: render(e) })) ) })) ``` `res.stream` — HttpClientResponse.stream: Stream. Yes exists. `Stream.filterMap` exists. `Stream.splitLines` exists. `Stream.unwrapEffect` exists. `Stream.decodeText()` exists. JSON.parse inside — sync, fine, no async/await anywhere. Return `{ complete, stream }`. Note cfg.apiKey: Option. Redacted.value. Good. Config.ts: ```ts import { Config, Context, Effect, Layer, Redacted } from "effect" export interface ConfigShape { readonly maxSteps: number readonly toolConcurrency: number readonly toolTimeout: Duration.Duration readonly requestTimeout: Duration.Duration readonly model: string readonly baseUrl: string readonly apiKey: Option readonly systemPrompt: string } export class HarnessConfig extends Context.Tag("harness/Config")() {} export const ConfigLive = Layer.effect(HarnessConfig, Effect.all({ maxSteps: Config.integer("AGENT_MAX_STEPS").pipe(Config.withDefault(8)), toolConcurrency: Config.integer("AGENT_TOOL_CONCURRENCY").pipe(Config.withDefault(4)), toolTimeout: Config.duration("AGENT_TOOL_TIMEOUT").pipe(Config.withDefault(Duration.seconds(10))), requestTimeout: Config.duration("AGENT_REQUEST_TIMEOUT").pipe(Config.withDefault(Duration.seconds(30))), model: Config.string("AGENT_MODEL").pipe(Config.withDefault("gpt-4o-mini")), baseUrl: Config.string("AGENT_BASE_URL").pipe(Config.withDefault("https://api.openai.com/v1")), apiKey: Config.option(Config.redacted("OPENAI_API_KEY")), systemPrompt: Config.string("AGENT_SYSTEM_PROMPT").pipe(Config.withDefault( "You are a tool-using agent. Prefer tools over guessing. Stop when the task is done." )) })) ``` `Config.option` exists (Config.option(config)). `Config.duration` exists → Config. `Config.integer` — hmm, does Config.integer exist? Config module has: string, number, integer, boolean, redacted, duration, option, withDefault, map... I'm fairly sure `Config.integer` exists. Yes. `Effect.all({...})` with struct of effects — yes returns Effect. Duration.seconds returns Duration — `Duration.seconds(10)`. withDefault takes Duration value. Config.duration decodes "10s" etc. good. Events.ts: ```ts import { Context, Effect, Layer, Queue, Stream } from "effect" import type { ToolCall } from "./Domain.js" export type AgentEvent = | { readonly _tag: "RunStarted"; readonly goal: string } | { readonly _tag: "StepStarted"; readonly step: number } | { readonly _tag: "LlmTurn"; readonly step: number; readonly text: string; readonly toolCalls: ReadonlyArray } | { readonly _tag: "ToolStarted"; readonly step: number; readonly call: ToolCall } | { readonly _tag: "ToolFinished"; readonly step: number; readonly call: ToolCall; readonly ok: boolean; readonly elapsedMs: number } | { readonly _tag: "RunFinished"; readonly steps: number; readonly text: string } export class Events extends Context.Tag("harness/Events") Effect readonly subscribe: Stream.Stream }>() {} export const EventsLive = Layer.effect(Events, Effect.gen(function* () { const queue = yield* Queue.unbounded() return { publish: (e) => Queue.offer(queue, e).pipe? ``` `Queue.offer` returns Effect — need Effect: `Effect.asVoid(Queue.offer(queue, e))`. subscribe: `Stream.fromQueue(queue)` — but Stream.fromQueue shuts down when queue ends... queue never ends. Also multiple consumption: single consumer; fromQueue also debur? fine. Note: `Stream.fromQueue` signature `(queue, options?)`. ok. Hmm — one concern: `Queue.unbounded()` — is it Effect? Yes I'm confident: `yield* Queue.unbounded()` is standard v3. Return shape: `{ publish: (e) => Effect.asVoid(Queue.offer(queue, e)), subscribe: Stream.fromQueue(queue) }`. Layer.effect(Events, gen) fine. Agent.ts: ```ts import { Chunk?, Clock, Context, Effect, Either, Layer, Metric, Option, Schedule } from "effect" import { Llm, LlmError } from "./Llm.js" import { HarnessConfig } from "./Config.js" import { Events } from "./Events.js" import { ToolRegistry } from "./Tools.js" import { InvalidToolArgs, StepLimitExceeded, ToolNotFound } from "./Errors.js" import type { Completion, Message, ToolCall, ChatRequest } from "./Domain.js" import { Schema } from "effect" export interface AgentResult { readonly goal: string readonly text: string readonly steps: number readonly transcript: ReadonlyArray } export class Agent extends Context.Tag("harness/Agent") Effect? ``` Hmm — the Agent service shape methods' R. If I put FileSystem|HttpClient into the service shape's R, then consumers need those in R too. `agent.run` returns Effect<..., ..., ToolDeps> where ToolDeps = FileSystem | HttpClient. Declare in shape: `run: (goal: string) => Effect`. AgentError = LlmError | StepLimitExceeded. Service shape includes R — Context.Tag shape type includes Effect with R — that's fine; Tag carries R requirements. Then AgentLive: ```ts export const AgentLive = Layer.effect(Agent, Effect.gen(function* () { const cfgCtx = yield* HarnessConfig const llm = yield* Llm const tools = yield* ToolRegistry const events = yield* Events const stepsCounter = Metric.counter("harness_agent_steps") const toolCounter = Metric.counter("harness_tool_calls") const decodeArgs = (tool: Tool.Any, call: ToolCall) => { const schema = tool.parameters const decoded = typeof call.arguments === "string" ? Schema.decodeUnknown(Schema.parseJson(schema)) : Schema.decodeUnknown(schema) return decoded(call.arguments).pipe? ``` Hmm — decodeUnknown returns function (u) => Effect. Using it: `decoded(call.arguments)` returns Effect. Map error → InvalidToolArgs. Do: ```ts const decodeArgs = (tool: Tool.Any, call: ToolCall): Effect => { const parse = typeof call.arguments === "string" ? Schema.decodeUnknown(Schema.parseJson(tool.parameters)) : Schema.decodeUnknown(tool.parameters) return Effect.mapError(parse(call.arguments ?? {}), (e) => new InvalidToolArgs({ name: call.name, detail: e.message })) } ``` ParseError has .message — yes. Wait — generic I lost: decodeArgs returns unknown; tool.run(input: I) with I=any — ok since Tool.Any = Tool. runOneTool: ```ts const runOne = (call: ToolCall): Effect<{ ok: boolean; body: unknown }, never, ToolDeps> => Effect.gen(function* () { const found = yield* tools.get(call.name) if (Option.isNone(found)) { return yield* Effect.fail(new ToolNotFound({ name: call.name })) } const args = yield* decodeArgs(found.value, call) return yield* found.value.run(args) }).pipe( Effect.timeoutOption(cfgCtx.toolTimeout), Effect.map((o) => Option.isSome(o) ? { ok: true, body: o.value } : { ok: false, body: `timed out after ${Duration.toString?}` }), Effect.catchAll((e) => Effect.succeed({ ok: false, body: renderError(e) })), Effect.catchAllDefect((d) => Effect.succeed({ ok: false, body: `defect: ${d}` })) ) ``` `Effect.timeoutOption` — exists? I recall `Effect.timeoutOption: (duration) => (self) => Effect, E, R>` — yes v3 has Effect.timeoutOption. ok. `Effect.catchAllDefect` exists. Order: timeoutOption before catchAll — timeoutOption preserves E; then catchAll folds E→succeed. But timeoutOption with E=ToolNotFound|InvalidToolArgs|unknown — fine. Note: tool.run error channel unknown, so catchAll handler param type unknown — ok. execTool with events & metrics: ```ts const execTool = (step: number) => (call: ToolCall) => Effect.gen(function* () { const start = yield* Clock.currentTimeMillis yield* events.publish({ _tag: "ToolStarted", step, call }) const outcome = yield* runOne(call) const elapsed = (yield* Clock.currentTimeMillis) - start yield* Metric.increment(toolCounter) yield* events.publish({ _tag: "ToolFinished", step, call, ok: outcome.ok, elapsedMs: elapsed }) const message: Message = { role: "tool", toolCallId: call.id, content: JSON.stringify({ ok: outcome.ok, result: outcome.body }), isError: !outcome.ok } return message }) ``` Loop: ```ts const run = (goal: string) => Effect.gen(function* () { const transcript: Array = [] const push = (m: Message) => { transcript.push(m) } // sync; call via Effect? just call directly inside gen — fine (plain code) yield* events.publish({ _tag: "RunStarted", goal }) transcript.push({ role: "system", content: cfgCtx.systemPrompt }) transcript.push({ role: "user", content: goal }) const toolSpecs = yield* tools.specs for (let step = 1; ; step++) { if (step > cfgCtx.maxSteps) { return yield* Effect.fail(new StepLimitExceeded({ maxSteps: cfgCtx.maxSteps })) } yield* events.publish({ _tag: "StepStarted", step }) yield* Metric.increment(stepsCounter) const request: ChatRequest = { messages: transcript, tools: toolSpecs } const completion = yield* llm.complete(request).pipe( Effect.retry(retryPolicy), Effect.withSpan("agent.llm-turn", { attributes: { step } }) ) yield* events.publish({ _tag: "LlmTurn", step, text: completion.text, toolCalls: completion.toolCalls }) if (completion.toolCalls.length === 0) { transcript.push({ role: "assistant", content: completion.text, toolCalls: [] }) yield* events.publish({ _tag: "RunFinished", steps: step, text: completion.text }) return { goal, text: completion.text, steps: step, transcript: transcript as ReadonlyArray } satisfies AgentResult } transcript.push({ role: "assistant", content: completion.text, toolCalls: completion.toolCalls }) const toolMessages = yield* Effect.forEach(completion.toolCalls, execTool(step), { concurrency: cfgCtx.toolConcurrency, discard: false }) for (const m of toolMessages) transcript.push(m) } }).pipe( Effect.withSpan("agent.run", { attributes: { "agent.goal": goal } }) ) return { run } })) ``` Wait: for-of over toolMessages with push inside gen — fine. Could use `Effect.forEach(..., {discard:false})` then push loop. ok. The `return yield* Effect.fail(...)` inside gen: typing: gen returns AgentResult | never... The gen's return type: AgentResult; fail typed. Fine. Type of `run`: Effect? cfgCtx, llm, tools, events already resolved into closure — their requirements captured at layer build; run's remaining R = whatever the gen body requires: events.publish — Events already resolved (service value), so no R from it. execTool → runOne → found.value.run → R: FileSystem | HttpClient. So R = FileSystem | HttpClient. Also Clock — built-in? Clock is a default service in runtime — `yield* Clock.currentTimeMillis` requires Clock? Clock is provided by default runtime (no requirement in type). Right: Clock has a default (Effect's default services include Clock); using Clock in Effect adds requirement Clock to type? Hmm — `Clock.currentTimeMillis: Effect` — its type R includes Clock? Clock module: `Clock.currentTimeMillis: Effect` — I believe the Clock is part of default services and NOT tracked in R (like Console? no, Console IS tracked...). Let me think: In Effect v3, `Clock` is a service but with a "default" provided automatically — the type of `Clock.currentTimeMillis` is `Effect` (no Clock in R) because default services (Clock, Console? no...) — Actually default services: Clock is provided via `Effect.clock`... I recall `Clock.currentTimeMillis: Effect` without R=Clock because Clock is always available (default). Yes — Clock and Random have defaults; Console/FileSystem do not. So fine. But wait — llm.complete pipe with Effect.retry(retryPolicy): retryPolicy type Schedule<...> — `Schedule.jittered` on intersected schedule: type Schedule? intersect of exponential & recurs: fine as Schedule. Effect.retry accepts `Schedule`? If policy R must be Never — jittered keeps R=never. Out type irrelevant. ok. One typing subtlety: `Effect.forEach(completion.toolCalls, execTool(step), { concurrency: cfgCtx.toolConcurrency })` — execTool(step) returns Effect; forEach → Effect, never, ToolDeps>. ok. But execTool defined inside AgentLive builder closure with access to cfgCtx/tools/events — yes, define inside. Type of service shape: ```ts export class Agent extends Context.Tag("harness/Agent")() {} export interface AgentShape { readonly run: (goal: string) => Effect } ``` AgentError = LlmError | StepLimitExceeded. AgentEnv = FileSystem | HttpClient (from tools). But does the actual `run` effect's R match exactly FileSystem | HttpClient? The gen body: `llm.complete` (no R), `tools.get` (no R), `events.publish` (no R), tool.run (FileSystem | HttpClient), Clock (none), Metric (none). Plus span/attrs none. So R = FileSystem | HttpClient. And error: LlmError | StepLimitExceeded (runOne errors folded into success). Good. To be safe in AgentShape use the union — assignability requires shape's declared R ⊇ actual? The service value returned must satisfy AgentShape: run: Effect<..., AgentError, AgentEnv> — actual Effect — matches if I declare AgentEnv = FileSystem | HttpClient. If actual R were narrower, still assignable (R covariant). ok. Harness.ts: ```ts import { Console, Effect, Layer } from "effect" import { NodeContext, NodeHttpClient } from "@effect/platform-node" import { Agent, AgentLive, type AgentResult } from "./Agent.js" import { ConfigLive } from "./Config.js" import { EventsLive } from "./Events.js" import { Mock, type MockStep } from "./Providers/Mock.js" import { ToolRegistry, builtins } from "./Tools.js" export interface Scenario { readonly name: string readonly goal: string readonly script: ReadonlyArray readonly expect: (outcome: ScenarioOutcome) => boolean } export type ScenarioOutcome = | { readonly _tag: "Success"; readonly result: AgentResult } | { readonly _tag: "Failure"; readonly error: unknown } export type ScenarioReport = { readonly name: string; readonly pass: boolean; readonly detail: string } const layersFor = (script: ReadonlyArray) => { const platform = Layer.mergeAll(ConfigLive, NodeContext.layer, NodeHttpClient.layer) return Layer.provide( AgentLive, Layer.mergeAll(platform, Mock.layer(script), ToolRegistry.layerWith(builtins), EventsLive) ) } ``` Wait AgentLive also requires Events — EventsLive included. Config in platform. Llm via Mock.layer. ToolRegistry layerWith. Good. ```ts export const runScenario = (s: Scenario): Effect => Effect.gen(function* () { const outcome = yield* Effect.gen(function* () { const agent = yield* Agent const result = yield* agent.run(s.goal) return { _tag: "Success", result } as ScenarioOutcome }).pipe( Effect.catchAll((e) => Effect.succeed({ _tag: "Failure", error: e } as ScenarioOutcome)), Effect.provide(layersFor(s.script)), Effect.withSpan("harness.scenario", { attributes: { scenario: s.name } }) ) const pass = yield* Effect.try({ try: () => s.expect(outcome), catch: (e) => ... }) ``` expect may throw; use Effect.try → boolean... simpler: wrap: ```ts const pass = Effect.runSync? no — keep effect: const pass = yield* Effect.try({try: () => s.expect(outcome), catch: ...}).pipe(Effect.catchAll(() => Effect.succeed(false))) ``` detail: if failure include error message: `renderError(outcome._tag === "Failure" ? outcome.error : "expectation failed")`. print: return report; main prints. ```ts export const runAll = (scenarios: ReadonlyArray) => Effect.forEach(scenarios => runScenario(s), { concurrency: "unbounded" }) // wait signature Effect.forEach(items, f, options) ``` `Effect.forEach(scenarios, runScenario, { concurrency: "unbounded" })`. Then print summary: ```ts export const runSuite = (name: string, scenarios: ReadonlyArray) => Effect.gen(function* () { yield* Console.log(`\n▶ suite: ${name}`) const reports = yield* Effect.forEach(scenarios, runScenario, { concurrency: "unbounded" }) for (const r of reports) { yield* Console.log(` ${r.pass ? "✅" : "❌"} ${r.name}${r.pass ? "" : ` — ${r.detail}`}`) } const failed = reports.filter(r => !r.pass).length yield* Console.log(` ${reports.length - failed}/${reports.length} passed`) yield* Console.log? set exit code: yield* Effect.sync(() => { process.exitCode = failed === 0 ? 0 : 1 }) return reports }) ``` Hmm process in harness — Node-specific; acceptable (or move exit code to Main). Put exitCode in Main. Keep harness pure-ish: return reports. Scenarios definitions (in Harness or separate Scenarios.ts): ```ts export const defaultScenarios: ReadonlyArray = [ { name: "tool round-trip", goal: "What is the current time?", script: [ { _tag: "ToolCall", tool: "clock.now", args: {} }, { _tag: "RepeatToolResult", prefix: "Here it is: " } ], expect: (o) => o._tag === "Success" && o.result.steps === 2 && o.result.text.startsWith("Here it is:") }, { name: "unknown tool is recoverable", goal: "Do something impossible", script: [ { _tag: "ToolCall", tool: "nope.doesNotExist", args: {} }, { _tag: "RepeatToolResult", prefix: "Recovered from tool error: " } ], expect: (o) => o._tag === "Success" && o.result.text.startsWith("Recovered") }, { name: "step limit enforced", goal: "Loop forever", script: Array.from({ length: 12 }, () => ({ _tag: "ToolCall" as const, tool: "echo", args: { message: "again" } })), expect: (o) => o._tag === "Failure" && o.error._tag === "StepLimitExceeded" } ] ``` Note config maxSteps default 8 → 12 calls exhaust. But `o.error._tag` — error typed unknown in Failure? If Failure error typed as unknown, `.error._tag` fails TS. Type ScenarioOutcome Failure error as `unknown`? Then expect can't access _tag. Cast in scenario: `(o.error as {_tag:string})._tag`. Or type Failure error as `AgentError`? runScenario catchAll typed on agent.run error = AgentError — so failure outcome error: AgentError. Define: ```ts | { readonly _tag: "Failure"; readonly error: AgentError } ``` AgentError = LlmError | StepLimitExceeded — has _tag. Good: `o.error._tag === "StepLimitExceeded"` works. Also scenario 3 with concurrency etc. Fine. Main.ts: ```ts import { Console, Effect, Option } from "effect" import { NodeContext, NodeHttpClient, NodeRuntime } from "@effect/platform-node" import { Agent, AgentLive } from "./Agent.js" import { ConfigLive } from "./Config.js" import { EventsLive, type AgentEvent } from "./Events.js" import { LlmLive } from "./Providers/index.js"? ``` Provider selection — put in Providers/LlmLive? I'll create `src/Providers/OpenAi.ts` exporting `layer`, `Providers/Mock.ts` exporting `layer` & `demoScript`, and Main composes: ```ts const LlmLive = Layer.unwrapEffect(Effect.map(Config.string("AGENT_PROVIDER").pipe(Config.withDefault("mock")), (p) => p === "openai" ? OpenAiLayer : Mock.layer(demoScript))) ``` But OpenAi.layer requires HttpClient + Config — unwrapEffect requires Config only + result layer req HttpClient. Type: Layer. Then Layer.provide(LlmLive, platform). Mock.layer requires nothing. Union type of the two layers: Layer | Layer — union ok for provide? Layer.provide(self, that) — union of layers acceptable? Type-wise union should be fine. Maybe annotate: `const LlmLive: Layer.Layer = ...`. Mock.layer as Layer assignable to Layer (R covariant: never ≤ HttpClient). good. Full wiring in Main: ```ts const platform = Layer.mergeAll(ConfigLive, NodeContext.layer, NodeHttpClient.layer) const Full = Layer.provide(AgentLive, Layer.mergeAll(platform, Layer.provide(LlmLive, platform), ToolRegistry.layerWith(builtins), EventsLive)) ``` CLI program: ```ts const args = yield* Effect.sync(() => process.argv.slice(2)) if (args[0] === "--demo") { yield* runSuite("agent-harness self-check", defaultScenarios); return } const goal = args.join(" ") if (goal.trim() === "") { yield* Console.error("usage: ..."); return } const events = yield* Events const agent = yield* Agent // watcher fiber const watcher = yield* Effect.forkDaemon(Stream.runForEach(events.subscribe, prettyEvent)) const result = yield* agent.run(goal) yield* Fiber.interrupt(watcher) yield* Console.log(`\n${result.text}`) yield* Console.log(`(${result.steps} steps)`) ``` prettyEvent: ```ts const prettyEvent = (e: AgentEvent): Effect => e._tag === "ToolStarted" ? Console.log(` ⚙ ${e.call.name}(${truncateArgs(e.call.arguments)})`) : e._tag === "ToolFinished" ? Console.log(` ${e.ok ? "✔" : "✖"} ${e.call.name} (${e.elapsedMs}ms)`) : Effect.void ``` Then `NodeRuntime.runMain(program.pipe(Effect.provide(Full)))`. Wait — program requires Agent + Events (from Full) — provided. But note program uses `Stream` — import Stream, Fiber. Also `process.exitCode` set inside runSuite — ok Node. Edge: with provider=openai and no OPENAI_API_KEY, complete will fail at request (401) — fine, harness retries 3× then fails — acceptable prototype behavior; mention. Also for the watcher: uses events.subscribe Stream — consumed once by CLI. In demo mode, EventsLive provided but unsubscribed — events accumulate in unbounded queue — fine. Hmm, one more: `Stream.runForEach` returns Effect — stream error never; ok. Fiber.interrupt returns Effect — yield* fine. Also should I use `Effect.forkScoped`? Main has no scope; forkDaemon + manual interrupt. But if agent fails, watcher fiber lingers — runMain on error path exits process anyway. Add `Effect.ensuring(Fiber.interrupt(watcher))`? Use `Effect.ensuring` for cleanliness: ```ts yield* agent.run(goal).pipe(Effect.ensuring(Fiber.interrupt(watcher))) ``` Nice — demonstrates ensuring. But we already yield agent.run; restructure: ```ts const result = yield* agent.run(goal).pipe(Effect.tap(...)?, Effect.ensuring(Fiber.interrupt(watcher))) ``` ok. Also add graceful note: NodeRuntime.runMain installs SIGINT handler → interrupts → agent's in-flight HTTP aborted (interruption propagates) — mention in notes. package.json: ```json { "name": "agent-harness", "type": "module", "scripts": { "demo": "tsx src/main.ts --demo", "agent": "tsx src/main.ts" }, "dependencies": { "effect": "^3.14.0", "@effect/platform": "^0.80.0", "@effect/platform-node": "^0.84.0" }, "devDependencies": { "tsx": "^4.19.0", "typescript": "^5.7.0", "@types/node": "^22.0.0" } } ``` Version pairing anxiety: effect 3.14 pairs with platform 0.80? Effect 3.12 ↔ platform 0.76/77? Honestly exact pairing: effect@3.13.0 ↔ @effect/platform@0.77.x? I recall effect 3.10 ↔ platform 0.69, 3.12 ↔ 0.74?, 3.13 ↔ 0.77, 3.14 ↔ 0.78? Not certain. Safer: instruct `npm i effect @effect/platform @effect/platform-node` letting npm resolve compatible latest, and give package.json without hard pins (use "latest"? that's ugly). Compromise: dependencies with `^` ranges but note "run npm install to resolve current compatible versions" or just provide the install command and a minimal package.json without versions? A package.json without deps is odd. I'll include the deps with caret ranges and add a note: "if version mismatch errors appear, install the three packages together so npm picks a compatible set." Good enough for a prototype. tsconfig: ```json { "compilerOptions": { "target": "ES2022", "lib": ["ES2022"], "module": "ESNext", "moduleResolution": "Bundler", "strict": true, "noUncheckedIndexedAccess": true, "skipLibCheck": true, "exactOptionalPropertyTypes": false, "types": ["node"] }, "include": ["src"] } ``` noUncheckedIndexedAccess with `decoded.choices[0]` handled via `?? undefined` check — I used `choice === undefined` check — good. args[0] check — `args[0] === "--demo"` fine (string|undefined comparison ok). process.exitCode — @types/node. Now double-check a few Effect APIs once more: - `Effect.timeoutOption(duration)` — hmm, actual name? There's `Effect.timeoutOption` in v3: returns Effect, E>. Yes I'm fairly confident it exists (added alongside timeoutTo/timeoutFail). Signature `Effect.timeoutOption: (duration: DurationInput) => (effect) => Effect, E, R>`. I'll use it. - `Effect.timeoutFail({ duration, onTimeout })` — exists v3 (data-last). Yes. - `Schedule.intersect` — exists. `Schedule.jittered` — exists as combinator `Schedule.jittered(self)`? There's `Schedule.jittered` and `Schedule.jitteredWith`. `jittered: (self) => Schedule`. ok. - `Schedule.exponential(base: DurationInput, factor?: number)` ok. `Schedule.recurs(n)` ok — v3 name recurs (yes). - `Effect.retry` with schedule — ok. - `Metric.counter(name)` — v3: `Metric.counter("name", {bigint?})` returns Counter; `Metric.increment(counter)`. ok. Maybe add options {description}? skip. - `Stream.fromQueue` — exists (alias fromQueue? I recall `Stream.fromQueue(queue, options?)` yes). - `Queue.offer(queue, value): Effect` ok. - `Stream.runForEach(stream, f): Effect` ok. - `Effect.forkDaemon` ok. `Fiber.interrupt(fiber): Effect>` ok. - `Effect.ensuring` ok. - `Layer.unwrapEffect(effect)` ok. - `Effect.catchAllDefect` ok. - `Effect.mapError` ok. - `Schema.parseJson(schema)` — exists in effect/Schema v3: `Schema.parseJson: { (schema): SchemaClass; (): SchemaClass }` — I'm fairly confident both forms exist (compose with parseJson). Yes: `Schema.parseJson(Schema.Struct({...}))` documented. - `Schema.decodeUnknown(schema)` returns function (u) => Effect. ok. - `JSONSchema.fromSchema(schema)` — in `effect/JSONSchema` module: `JSONSchema.fromSchema(schema, options?)` — exists (v3.10+ moved JSONSchema into effect). I'll import from "effect". Signature returns JSONSchema.JSONSchema. ok. Note: For Schema.Schema type param — fromSchema accepts `Schema.Schema.All | ...` fine with any. - `Schema.Struct({})` empty — fine (type {}). - `Schema.NullOr` — exists. `Schema.optional` — exists. - `Schema.Literal` not used — fine. - `Redacted` — in effect v3.11+: `Redacted` module; `Config.redacted`; `Redacted.value`. ok. For older effect it was Secret — note in README to use effect ≥3.11. I'll mention versions. - `Context.Tag` constructor form: `Context.Tag("id")()` — correct v3. - `Effect.forEach(iterable, f, { concurrency: number | "unbounded" })` — correct. - `Option.fromNullable` — used in Mock maybe. - `Duration.seconds(n)` returns Duration — `DurationInput` accepted by Effect.timeout etc. ok. - `Effect.withSpan(name, { attributes })` ok. - `Effect.provide(layer)` ok. - `Layer.mergeAll` ok. `Layer.provide(self, that)` ok. - `NodeRuntime.runMain(effect)` — signature: `runMain: (effect: Effect) => void`? Actually `NodeRuntime.runMain` accepts options then effect? I recall `NodeRuntime.runMain(effect)` works (options optional first param). There's also `runMain({ disableErrorReporting?... })`. I'll use `NodeRuntime.runMain(app)` where app: Effect. Our program: Effect after provide. good. Hmm wait — NodeRuntime.runMain requires effect error channel be `unknown`-ish? It accepts `Effect`? Our catchAll in scenario handles agent errors; runSuite returns void-ish. Console.error path. So final app E = never. ok. One more consideration: `Console.log` — from "effect" — `Console.log(...args): Effect` — hmm, actually the Console module: `Console.log: (...args: ReadonlyArray) => Effect`? There's `Console.log` returning Effect? It's fine either way — yield* discards. But does Console require the Console service in R? `Console.log` — in effect v3, the default Console is provided by default runtime; type of Console.log is Effect? I recall Console functions have R = never because a default console is in DefaultServices. Yes — Console is a default service; Console.log typed Effect. ok. Also careful with `Effect.sync(() => { process.exitCode = ... })` — fine. Also in Mock complete — `req` unused in ToolCall/RepeatToolResult steps except Repeat scanning messages: uses req.messages. ok. Mock layer needs `Ref` import; complete: ```ts export const layer = (script: ReadonlyArray) => Layer.effect(Llm, Effect.gen(function* () { const cursor = yield* Ref.make(0) const nextCompletion = (req: ChatRequest): Effect => Effect.gen(function* () { const n = yield* Ref.getAndUpdate(cursor, (n) => n + 1) const step = script[n] if (step === undefined) { return { text: "[mock] script exhausted", toolCalls: [], finishReason: "stop" } } switch (step._tag) { case "Text": return { text: step.text, toolCalls: [], finishReason: "stop" } case "ToolCall": { const call: ToolCall = { id: `call_${n + 1}`, name: step.tool, arguments: step.args ?? {} } return { text: "", toolCalls: [call], finishReason: "tool_calls" } } case "RepeatToolResult": { const lastTool = [...req.messages].reverse().find((m) => m.role === "tool") const content = lastTool && lastTool.role === "tool" ? lastTool.content : "(no tool result found)" return { text: `${step.prefix ?? ""}${content}`, toolCalls: [], finishReason: "stop" } } } }) return { complete: (req) => nextCompletion(req), stream: (req) => Stream.unwrap(Effect.map(nextCompletion(req), (c) => Stream.make(...chunk(c.text)))) } })) ``` chunk: split into 8-char pieces: ```ts const chunk = (text: string): Array => text.length === 0 ? [] : text.match(/.{1,8}/gs) ?? [text] ``` regex `.{1,8}/gs` fine (s flag for newlines). ok. TS narrowing: `lastTool && lastTool.role === "tool"` then `lastTool.content` — role "tool" branch has toolCallId & content — ok. Actually simpler: ```ts const lastTool = req.messages.findLast((m) => m.role === "tool") ``` `Array.prototype.findLast` — ES2022 lib — good with target ES2022. Then narrow: `lastTool?.role === "tool"`? TS can't narrow union via findLast predicate easily — findLast returns Message | undefined; predicate true ensures role==="tool" only if predicate typed as (m: Message) => m is ToolMessage. Define type guard: ```ts const isTool = (m: Message): m is Extract => m.role === "tool" const lastTool = [...req.messages].reverse().find(isTool) ``` clean. Use `req.messages.findLast(isTool)`. Completion type — define usage?: { promptTokens: number; completionTokens: number } — mock omits (optional). ok. Now encodeMessage in OpenAi: ```ts const encodeMessage = (m: Message): unknown => { switch (m.role) { case "assistant": return { role: "assistant", content: m.content, ...(m.toolCalls.length > 0 ? { tool_calls: m.toolCalls.map((c) => ({ id: c.id, type: "function", function: { name: c.name, arguments: typeof c.arguments === "string" ? c.arguments : JSON.stringify(c.arguments ?? {}) } })) } : {}) } case "tool": return { role: "tool", tool_call_id: m.toolCallId, content: m.content } default: return { role: m.role, content: m.content } } } ``` m.role "system"/"user" via default — role type string ok. encodeTool: ```ts const encodeTool = (t: ToolSpec) => ({ type: "function", function: { name: t.name, description: t.description, parameters: t.parametersJsonSchema } }) ``` Now double check `HttpClientRequest.bodyUnsafe` — signature `(contentType: string, content: Body.Body["..."])`? I believe: `bodyUnsafe: (contentType: string, content: string | ArrayBuffer | Uint8Array) => (self: HttpClientRequest) => HttpClientRequest`. Hmm, or is it `(body: Body)`? There's `HttpClientRequest.body = (body: Body.Body) => (self)`. And `Body.unsafeJson(json)`. Two safe routes: - `HttpClientRequest.body(Body.unsafeJson(payload))` — but is `Body.unsafeJson` present? I recall `Body.unsafeJson: (json: unknown) => Body` — yes I'm fairly confident Body.unsafeJson exists (and Body.json as Effect? no...). Hmm. Actually now I remember more concretely from @effect/platform source: HttpClientRequest.ts exports: ```ts export const bodyJson = (json: unknown): Effect ... export const bodyUnsafe = (contentType: string, content: string | ArrayBuffer | Uint8Array): (self: HttpClientRequest) => HttpClientRequest ... ``` Hmm no wait. Let me think about actual doc examples I've seen in the wild recently (effect-platform 0.7x): ```ts import { HttpClientRequest } from "@effect/platform" const request = HttpClientRequest.post("https://example.com").pipe( HttpClientRequest.bodyUnsafe("application/json", JSON.stringify({ hello: "world" })) ) ``` Yes — I've seen exactly `bodyUnsafe("application/json", ...)`. I'm confident enough. Alternatively even safer dual: `HttpClientRequest.bodyUnsafe` is used in effect's own tests. Go. Bearer: `HttpClientRequest.bearerToken("token")` — exists (also `bearerToken` handles Redacted? there's `HttpClientRequest.bearerToken(token: string)`). ok. `response.text` — HttpClientResponse has `.text: Effect` property. I've seen `yield* response.text`. ok. And `.stream: Stream`. ok. `http.execute(request)` — returns Effect. With Effect.scoped wrapper for text consumption. Let me include Effect.scoped in both complete & stream & httpGet tool to be safe. For stream: `http.execute(request)` inside Stream.unwrapEffect — the response stream consumption must be within scope... Stream.unwrapEffect runs the effect, gets response, then streams body — scope closes when? The Effect<..., Scope> requirement must be satisfied — Stream.unwrapEffect would require Scope in R of the stream?? That leaks Scope into stream R — bad. Proper: `Stream.unwrapScoped(Effect.gen(... http.execute ... map(res => res.stream ...)))` — unwrapScoped provides scope per subscription. Yes! Use `Stream.unwrapScoped` for the SSE stream. ```ts const stream = (req: ChatRequest): Stream.Stream => Stream.unwrapScoped(Effect.gen(function* () { const payload = JSON.stringify(bodyOf(req, true)) const request = authorize(HttpClientRequest.post(endpoint).pipe(HttpClientRequest.bodyUnsafe("application/json", payload))) const response = yield* http.execute(request).pipe( Effect.mapError((e) => new LlmError({ reason: render(e) })) ) return response.stream.pipe( Stream.decodeText(), Stream.splitLines, Stream.filterMap(parseSseLine), Stream.mapError((e) => new LlmError({ reason: render(e) })) ) })) ``` Hmm — mapError on execute: HttpClientError → LlmError ok. Inside unwrapScoped, scope provided by Stream when running. Good. Note: status check omitted for stream (prototype; note it). Actually `Stream.mapError` on response.stream handles ResponseError from body reads. ok. For complete with Effect.scoped: ```ts const response = yield* http.execute(request).pipe( Effect.scoped? ``` Wait — Effect.scoped wraps and provides Scope; but I also want timeoutFail — order: ```ts const response = yield* http.execute(request).pipe( Effect.timeoutFail({ duration: cfg.requestTimeout, onTimeout: () => new LlmError({ reason: "timeout" }) }), Effect.scoped ) const text = yield* response.text // ← DANGER: scope already closed! ``` Must consume body inside scope: ```ts const readBody = Effect.gen(function* () { const response = yield* http.execute(request) const text = yield* response.text return { response, text } }).pipe(Effect.scoped) ``` Then use response.status + text after — status is plain field, fine. Implement: ```ts const send = (request: HttpClientRequest): Effect<{ status: number; body: string }, LlmError> => Effect.gen(function* () { const response = yield* http.execute(request) const body = yield* response.text return { status: response.status, body } }).pipe( Effect.scoped, Effect.timeoutFail({ duration: cfg.requestTimeout, onTimeout: () => new LlmError({ reason: `request timed out` }) }), Effect.mapError((e) => e instanceof LlmError ? e : new LlmError({ reason: render(e) })) ) ``` timeoutFail error type: LlmError; mapError folds others (HttpClientError, ResponseError). But careful — timeoutFail's onTimeout typed to produce E_new; after timeoutFail, E = LlmError | HttpClientError | ResponseError. mapError folds all → LlmError. ok. Actually does timeoutFail on failure of scope interruption matter — fine. Hmm: `Effect.timeoutFail` — parameter is object `{ duration, onTimeout }` — yes v3. Also `render` helper duplicated? Put in Llm.ts export? Put in Errors or a small `src/Support.ts`? Inline small `renderError` in OpenAi and Agent separately — fine, or define once in Llm.ts and import. I'll define `export const renderError = (e: unknown): string => e instanceof Error ? e.message : String(e)` in Llm.ts (or Errors.ts). Errors.ts good. Now Agent's retryPolicy — retry applies to LlmError. Note Effect.retry default retries all errors — with schedule bounded. ok. Now, the Agent uses `Effect.forEach` for tool calls with concurrency — and tool messages order: forEach preserves order (collect in order) — good for tool_call_id matching (order preserved even with concurrency). One subtle correctness thing: OpenAI expects each tool result message with matching tool_call_id — we keep call.id. Mock ignores. good. ChatRequest includes tools; Mock ignores. good. Now `ToolRegistry.layerWith(builtins)` — define: ```ts export const layerWith = (tools: ReadonlyArray): Layer.Layer => Layer.effect(ToolRegistry, Effect.sync(() => { const map = new Map(tools.map((t) => [t.name as string, t])) return { get: (name: string) => Effect.succeed(Option.fromNullable(map.get(name))), specs: Effect.sync(() => Array.from(map.values(), (t) => ({ name: t.name, description: t.description, parametersJsonSchema: JSONSchema.fromSchema(t.parameters) }))) } })) ``` No Ref needed if immutable after build — simpler, drops Ref usage... I wanted Ref somewhere to show statefulness — Mock uses Ref. fine. But `Effect.succeed`? `get` returns Effect — using Effect.sync closure each call ok. But layer builder: `Layer.effect(Tag, Effect.sync(...))`. ok. Also dynamic `register` method? Skip — prototype. Maybe keep register to show Ref + mutation: Eh — keep it minimal: immutable registry. Mock keeps Ref demo. Actually, let me add `register` with Ref anyway — it's 6 lines and makes "registry" meaningful (plugins can register at runtime). OK include Ref version: ```ts export const layerWith = (tools) => Layer.effect(ToolRegistry, Effect.gen(function* () { const map = yield* Ref.make(new Map(tools.map((t) => [t.name, t]))) return { get: (name) => Effect.map(Ref.get(map), (m) => Option.fromNullable(m.get(name))), register: (tool) => Ref.update(map, (m) => new Map(m).set(tool.name, tool)), specs: Effect.map(Ref.get(map), (m) => Array.from(m.values()).map(toSpec)) } })) ``` Map mutation in Ref.update — using immutable copy `new Map(m).set(...)` — set returns map — good (not mutating previous). JSONSchema.fromSchema typing: returns JSONSchema.JSONSchema — assign to unknown ok. Hmm `JSONSchema.fromSchema` might throw for unsupported schemas? Our schemas are simple structs. fine. Now the AgentShape: ```ts export interface AgentError = LlmError | StepLimitExceeded — TS interface for union? Use `export type AgentError = ...`. ``` Shape: ```ts export class Agent extends Context.Tag("harness/Agent") Effect.Effect }>() {} export type AgentEnv = FileSystem.FileSystem | HttpClient.HttpClient // hmm type refs ``` Type reference problem: importing classes as types: `import type { FileSystem } from "@effect/platform"` — FileSystem class usable as type = service. And `HttpClient` similarly. In Tools.ts I import values anyway (FileSystem, HttpClient, HttpClientRequest). For type aliases in Tools.ts: `type ToolDeps = FileSystem | HttpClient` — works since class types. But careful: `FileSystem` the class — its instance type is the service interface? For `class FileSystem extends Context.Tag(...)()()`, TS: the class's instance type is... Context.Tag instances are opaque; but the pattern makes `FileSystem` (type) equal `Service` via declaration merging? Hmm — actually the magic of `Context.Tag` class pattern: ```ts class MyTag extends Context.Tag("MyTag")() {} ``` then `MyTag` as a type IS `{ readonly a: number }` — yes, because Context.Tag's declaration makes the class's instance type equal the Shape type param (via `declare const` phantom). This is the documented pattern: `const value: MyTag = yield* MyTag`. Yes. So type refs work: `FileSystem | HttpClient`. OK. Also need Path? no. AgentLive R must include FileSystem | HttpClient via tool execution, plus nothing else external. In Layer.effect(Agent, gen(...)), the inner gen requires HarnessConfig, Llm, ToolRegistry, Events (services) — but those are resolved at build time via yield*, so resulting effect's R = FileSystem | HttpClient only (remaining), with E = never (build can't fail... Config defaults mean no ConfigError — right, all Config.withDefault/option → no ConfigError. Good, ConfigLive never fails.) So Layer — then final provide includes NodeContext (FileSystem) + NodeHttpClient (HttpClient). NodeContext.layer provides FileSystem — yes. Wait — does NodeContext.layer provide HttpClient? I don't think so. NodeHttpClient.layer provides HttpClient. Both merged. ok. Also for scenarios: platform includes both. ok. Main runMain with pretty errors: on StepLimitExceeded etc. — in CLI mode if agent fails, runMain pretty prints. ok. Let me also double check `Layer.effect(Agent, ...)` requirement propagation: AgentLive = Layer.effect(Agent, inner) where inner: Effect. So AgentLive: Layer. Provide with merge containing all → Full: Layer. But hold on — EventsLive provides Events; ToolRegistry.layerWith provides ToolRegistry; platform provides HarnessConfig + FileSystem (+ more); LlmProvided provides Llm. AgentLive R includes HarnessConfig, Llm, ToolRegistry, Events, FileSystem, HttpClient — all satisfied. One catch: `Layer.mergeAll(platform, ...)` — platform itself is mergeAll of three; reused twice (in LlmProvided and in Full) — memoized by reference — same instance, fine. Now — the `stream` method on Llm service for OpenAI uses cfg captured — cfg apiKey Option. Good. Type of Llm service shape stream: `(req: ChatRequest) => Stream.Stream`. In Main CLI, if provider is openai, optionally we could stream final answer — skip; watcher prints events. Hmm — actually let me reconsider whether to keep Llm.stream at all: it adds ~30 lines in OpenAi + 5 in Mock, and it's *used* nowhere. A reviewer might flag dead code; but as a prototype of a "complete harness", streaming API presence is plausible. I'll keep it but wire it: in CLI mode, after agent finishes... can't (already final). Alternative: add `--ask` mode: single Llm.stream call without agent — "raw completion mode" demonstrating streaming into terminal: ```ts // --ask "prompt": single streaming completion, no tools const ask = Effect.gen(function* () { const llm = yield* Llm yield* llm.stream({ messages: [{ role: "user", content: goal }], tools: [] }).pipe( Stream.decodeText? already strings, Stream.runForEach((chunk) => Console.write(chunk)) ) }) ``` `Console.write(chunk)` — Console.write: (text) => Effect — writes without newline. `Console.write` exists? Console module has `Console.log`, `Console.error`, `Console.unsafe.log`... `Console.write`? I recall `Console.write: (text: string) => Effect` exists (writes raw). Yes I believe Console.write exists. If unsure, use process.stdout.write in Effect.sync — but Console.write I'm fairly confident exists in effect. ok use Console.write; fallback comment. So CLI modes: `--demo` scenarios; `--ask ` streaming raw; default agent mode. Nice — all APIs used. Now check Stream.runForEach + Console.write flush — fine. Fiber ticker — dropped (watcher handles). ok. Now, "no async/await" audit: - No `async` keywords anywhere. - JSON.parse/JSON.stringify sync ok. - TextDecoder sync. - No Effect.tryPromise. - NodeRuntime.runMain is callback-based runtime entry. - process.argv sync. Also fibers, Effect.gen everywhere. One more effect-native flourish: `Effect.iterate`? Not needed. `Effect.loop`? Could use for scenario printing; keep simple. Also add graceful SIGINT note — NodeRuntime.runMain handles interrupts (prints "Interrupted"?). Mention. Also tests? Could add a minimal test file using @effect/vitest... That adds dependency + more length; maybe skip tests, the scenarios serve as self-tests. Mention that scenarios double as eval tests. Length control: This will be long (~450-600 lines total code). That's appropriate for "complete agent harness prototype". Keep prose tight: brief intro, tree, code blocks per file, run instructions, extension notes. Avoid excessive per-file commentary — 1-2 lines each. File-by-file final check on imports & details: **src/Domain.ts** ```ts export interface ToolCall { readonly id: string readonly name: string readonly arguments: unknown } export type Message = | { readonly role: "system"; readonly content: string } | { readonly role: "user"; readonly content: string } | { readonly role: "assistant"; readonly content: string; readonly toolCalls: ReadonlyArray } | { readonly role: "tool"; readonly toolCallId: string; readonly content: string; readonly isError: boolean } export interface ToolSpec { readonly name: string readonly description: string readonly parametersJsonSchema: unknown } export interface ChatRequest { readonly messages: ReadonlyArray readonly tools: ReadonlyArray readonly temperature: number } export interface Completion { readonly text: string readonly toolCalls: ReadonlyArray readonly finishReason: string readonly usage?: { readonly promptTokens: number; readonly completionTokens: number } } ``` **src/Errors.ts** ```ts import { Data } from "effect" export class LlmError extends Data.TaggedError("LlmError")<{ readonly reason: string; readonly status?: number }> {} export class StepLimitExceeded extends Data.TaggedError("StepLimitExceeded")<{ readonly maxSteps: number }> {} export class ToolNotFound extends Data.TaggedError("ToolNotFound")<{ readonly name: string }> {} export class InvalidToolArgs extends Data.TaggedError("InvalidToolArgs")<{ readonly tool: string; readonly detail: string }> {} export const renderError = (e: unknown): string => (e instanceof Error ? e.message : String(e)) ``` InvalidToolArgs detail: ParseError.message — ParseError extends TaggedError with message — yes ParseError has message. ok. **src/Config.ts** — as above. Import Option, Redacted, Config, Context, Effect, Layer, Duration. ConfigShape includes systemPrompt. Export type ConfigShape. Wait: `Config.duration("AGENT_TOOL_TIMEOUT")` decodes duration strings; withDefault(Duration.seconds(10)) — Config.withDefault accepts value type Duration. ok. **src/Llm.ts** ```ts import { Context, Data, Effect } from "effect" import { Stream } from "effect" import type { ChatRequest, Completion } from "./Domain.js" export class LlmError extends Data.TaggedError("LlmError")<{ readonly reason: string; readonly status?: number }> {} ``` Wait — LlmError both in Errors.ts and Llm.ts — pick one: keep in Errors.ts, import. Simpler: define all in Errors.ts. ok. ```ts import { Context, Stream } from "effect" import type { ChatRequest, Completion } from "./Domain.js" import type { LlmError } from "./Errors.js" export class Llm extends Context.Tag("harness/Llm") Stream... no Effect readonly streamText: (req: ChatRequest) => Stream.Stream }>() {} ``` **src/Tools.ts** ```ts import { Context, Effect, Layer, Option, Ref, Schema } from "effect" import { JSONSchema } from "effect" import { Clock } from "effect" import { FileSystem, HttpClient, HttpClientRequest } from "@effect/platform" import type { ToolSpec } from "./Domain.js" import { renderError } from "./Errors.js"? not needed here. export interface Tool { readonly name: string readonly description: string readonly parameters: Schema.Schema readonly run: (input: I) => Effect.Effect } export type AnyTool = Tool export class ToolRegistry extends Context.Tag("harness/ToolRegistry") Effect.Effect> readonly register: (tool: AnyTool) => Effect.Effect readonly specs: Effect.Effect> }>() {} export const layerWith = (tools: ReadonlyArray): Layer.Layer => Layer.effect(ToolRegistry, Effect.gen(function* () { const map = yield* Ref.make(new Map(tools.map((t) => [t.name, t]))) return { get: (name) => Effect.map(Ref.get(map), (m) => Option.fromNullable(m.get(name))), register: (tool) => Ref.update(map, (m) => new Map(m).set(tool.name, tool)), specs: Effect.map(Ref.get(map), (m) => Array.from(m.values()).map((t) => ({ name: t.name, description: t.description, parametersJsonSchema: JSONSchema.fromSchema(t.parameters) })) ) } })) // ---- built-ins ---- const MAX_TEXT = 8_000 export const echo: Tool<{ message: string }> = { ... } export const now: Tool> = { name: "clock.now", ... parameters: Schema.Struct({}), run: () => Effect.map(Clock.currentTimeMillis, (ms) => new Date(ms).toISOString()) } export const readFile: Tool<{ path: string }> = { ... } export const httpGetText: Tool<{ url: string }> = { ... } export const builtins: ReadonlyArray = [echo, now, readFile, httpGetText] ``` `Effect.map(Clock.currentTimeMillis, ...)` — Clock.currentTimeMillis is `Effect` — yes property-style? In v3: `Clock.currentTimeMillis: Effect` — accessed as `Clock.currentTimeMillis` (static). yield* Clock.currentTimeMillis. ok. Empty struct tool invocation: decode {} ok. OpenAI function with empty params schema {type:"object",properties:{}} fine. readFile uses `new TextDecoder()` global — Node ok. httpGetText: ```ts run: ({ url }) => Effect.gen(function* () { const http = yield* HttpClient const response = yield* http.execute(HttpClientRequest.get(url)) const body = yield* response.text return body.slice(0, MAX_TEXT) }).pipe(Effect.scoped) ``` Hmm — Effect.scoped around gen: the gen yields http.execute (needs Scope) and response.text within — scoped provides — good. Error channel: HttpClientError | ResponseError — assignable to unknown in Tool.run. ok. **src/Events.ts** as planned with Queue. Wait — check `Queue.unbounded` is Effect — yes. `Stream.fromQueue(queue)` — yes exists. Also note Stream.fromQueue takes options {capacity?}. fine. Also `Effect.asVoid(Queue.offer(queue, e))`. **src/Agent.ts** — as planned. Careful with `satisfies` and types. Also note `runOne` error type: union includes ToolNotFound | InvalidToolArgs | unknown → collapses to unknown. catchAll (e: unknown). fine. execTool content: JSON.stringify({ ok, result }) — if result is huge — truncate: `truncate(JSON.stringify(outcome.body), 4000)`? Keep: ```ts const clip = (s: string, max = 4000): string => (s.length > max ? s.slice(0, max) + "…" : s) ``` content: clip(JSON.stringify({ ok: outcome.ok, result: outcome.body })). Retry policy — define at module level in Agent.ts: ```ts const llmRetry: Schedule.Schedule = Schedule.exponential(Duration.millis(200), 2).pipe( Schedule.intersect(Schedule.recurs(3)), Schedule.jittered ) ``` Type annotation could fight inference; safer `const llmRetry = ...` without annotation. Schedule.intersect typing: Schedule intersect → Schedule<[Out, Out2]?...> — out type tuple — irrelevant. Effect.retry accepts any Schedule with In = error? Effect.retry(schedule) — schedule's In must accept the error type... With In=unknown? exponential's In = any? `Schedule.exponential` : Schedule? I think exponential: Schedule (In = unknown) — works for any error. recurs: Schedule? recurs In = any → fine. intersect keeps In=unknown. jittered same. So Effect.retry(llmRetry) typechecks. ok — no annotation. Metric: ```ts const stepsTotal = Metric.counter("harness_agent_steps_total") const toolCallsTotal = Metric.counter("harness_tool_calls_total") ``` `Metric.counter(name, { description? })` — v3 signature `Metric.counter(name, options?)`. ok. Events publish types: AgentEvent union — publishing with exact shapes ok. The gen return: `satisfies AgentResult` — use explicit annotation: ```ts const final: AgentResult = { goal, text, steps: step, transcript } return final ``` transcript is Array (mutable) — assign to ReadonlyArray ok. Also `Effect.withSpan` placement: on the whole run effect. Add `Effect.tapError`? optional; skip. Also nice: `Effect.logDebug` per step: `yield* Effect.logDebug(\`step ${step}: ${completion.toolCalls.length} tool call(s)\`)` — with default logger level Info, debug hidden; set via `Logger.minimumLogLevel`? In runMain, could set env `LOG_LEVEL=debug`. Mention. Keep a couple of logInfo calls. Hmm — built-in pretty logger prints timestamps & spans nicely; good enough. **src/Providers/Mock.ts** as planned. Import Llm, Domain types, Ref, Effect, Layer, Stream, Option? (findLast with guard). MockStep exported for scenarios. **src/Providers/OpenAi.ts** as planned. Wait — one more detail in OpenAI complete: `decoded.usage && {...}` — TS: `usage?: {...}` — assigning `undefined | obj` fine. But `decoded.usage && {...}` when usage undefined → `undefined` — but expression type `undefined | {..}` — ok. Cleaner: ```ts usage: decoded.usage === undefined ? undefined : { promptTokens: decoded.usage.prompt_tokens, completionTokens: decoded.usage.completion_tokens } ``` with noUncheckedIndexedAccess — decoded.usage optional field access fine. choices[0] with noUncheckedIndexedAccess → `choice` possibly undefined — handled. **src/Harness.ts** as planned + scenarios. Also needs AgentError type import. scenario 3 script: 12 echo calls; maxSteps default 8 → StepLimitExceeded at step 9. But wait — each step does one LLM call + tool exec; with maxSteps 8, loop fails when step=9 > 8. Script length 12 > 8 fine. Also scenario expect uses `o.error._tag` — ScenarioOutcome Failure error: AgentError — has _tag: "LlmError" | "StepLimitExceeded". good. **src/main.ts** as planned. `--ask` mode requires Llm service in R — Full provides Llm. good. Also main: `const goal = args.join(" ")` — args from argv.slice(2) — if args[0]==="--ask", prompt = args.slice(1).join(" "). Let me write main: ```ts import { Console, Effect, Fiber, Layer } from "effect" import { Stream } from "effect" import { NodeContext, NodeHttpClient, NodeRuntime } from "@effect/platform-node" import { AgentLive, Agent } from "./Agent.js" import { ConfigLive } from "./Config.js" import { Events, EventsLive } from "./Events.js" import { ToolRegistry, builtins } from "./Tools.js" import { Llm } from "./Llm.js" import { OpenAi } from "./Providers/OpenAi.js" import { Mock, demoScript } from "./Providers/Mock.js" import { runSuite, defaultScenarios } from "./Harness.js" import { Config } from "effect" const LlmLive: Layer.Layer = Layer.unwrapEffect( Effect.map( Config.string("AGENT_PROVIDER").pipe(Config.withDefault("mock")), (p) => (p === "openai" ? OpenAi.layer : Mock.layer(demoScript)) ) ) ``` Type annotation: unwrapEffect result Layer — the inner effect reads Config (module-level Config, not service) — Config reading in Effect adds error ConfigError, not R. So effect: Effect, ConfigError, never>? Wait — reading `Config.string` yields Effect. So unwrapEffect: Effect, ConfigError, never> → Layer. My annotation `Layer.Layer` wrong. Let it infer; annotate as: ```ts const LlmLive = Layer.unwrapEffect(...) ``` then `Layer.provide(LlmLive, platform)`. And ConfigError must be handled — Config.withDefault avoids failure? `Config.string("AGENT_PROVIDER").pipe(Config.withDefault("mock"))` — withDefault means no ConfigError (fallback). Effect.map keeps E=never? Config.string returns Effect — withDefault recovers error → Effect? Yes: withDefault provides default on missing → E = never. So unwrapEffect E = never. Full wiring: ```ts const platform = Layer.mergeAll(ConfigLive, NodeContext.layer, NodeHttpClient.layer) const Full = Layer.provide( AgentLive, Layer.mergeAll(platform, Layer.provide(LlmLive, platform), ToolRegistry.layerWith(builtins), EventsLive) ) ``` Program: ```ts const program = Effect.gen(function* () { const args = yield* Effect.sync(() => process.argv.slice(2)) if (args[0] === "--demo") { yield* runSuite("agent-harness self-check", defaultScenarios) return } const agent = yield* Agent const events = yield* Events if (args[0] === "--ask") { const llm = yield* Llm const prompt = args.slice(1).join(" ") yield* Stream.runForEach(llm.streamText({ messages: [{ role: "user", content: prompt }], tools: [], temperature: 0.2 }), (s) => Console.write(s)) yield* Console.log("") return } const goal = args.join(" ") if (goal.trim() === "") { yield* Console.error("usage: tsx src/main.ts | --demo | --ask ") return } const watcher = yield* Effect.forkDaemon(Stream.runForEach(events.subscribe, printEvent)) yield* agent.run(goal).pipe( Effect.ensuring(Fiber.interrupt(watcher)), Effect.tap((r) => Console.log(`\n● ${r.text}\n\n(${r.steps} step${r.steps === 1 ? "" : "s"})`)) ) }) NodeRuntime.runMain(Effect.provide(program, Full)) ``` Hmm — wait, `Effect.provide(program, Full)` — provide signature Effect.provide(effect, layer). ok. Also in --ask mode, if provider mock — streamText chunked words — fine. printEvent: ```ts const printEvent = (e: AgentEvent): Effect.Effect => { switch (e._tag) { case "RunStarted": return Console.log(`▶ goal: ${e.goal}`) case "StepStarted": return Console.log(`— step ${e.step}`) case "LlmTurn": return e.toolCalls.length > 0 ? Console.log(` ↔ model → ${e.toolCalls.map((c) => c.name).join(", ")}`) : Effect.void case "ToolStarted": return Console.log(` ⚙ ${e.call.name}`) case "ToolFinished": return Console.log(` ${e.ok ? "✔" : "✖"} ${e.call.name} (${e.elapsedMs}ms)`) case "RunFinished": return Effect.void } } ``` import type { AgentEvent } from "./Events.js". NodeRuntime.runMain(program-effect with layer provided). But program in --demo returns void; errors: runSuite can't fail. ok. One concern: `Effect.ensuring(Fiber.interrupt(watcher))` — ensures interrupt on both success & failure — but on success we interrupt watcher before continuing — that's what we want. Hmm — subtle: watcher consumes events.subscribe — Stream.fromQueue — if we interrupt after RunFinished published, but agent may have published after last consumption... trailing events unconsumed — cosmetic only. Also — printEvent returns Effect via switch — all branches Effect; LlmTurn branch ternary returns Console.log or Effect.void — ok. Now — does `NodeRuntime.runMain` exist and accept Effect? In @effect/platform-node: `NodeRuntime.runMain` — yes: `import { NodeRuntime } from "@effect/platform-node"; NodeRuntime.runMain(mainEffect)`. ok. It also handles SIGINT with interruption. Double-check `Effect.forkDaemon` — exists. ok. `Stream.runForEach` import Stream from effect. ok. `Console.write` — hmm — does effect's Console have `write`? Checking memory: Console module: `log`, `error`, `warn`?, `info`?, `trace`?, `unsafe.log`, `withConsole`... I believe there's `Console.write: (text: string) => Effect?` hmm. There IS `Console.write` in @effect/platform? No — `Console` in effect core: functions log, error, warn, info, trace, unsafe.log, unsafe.error, withConsole. I don't recall `Console.write`. Safer: `Effect.sync(() => process.stdout.write(s))` in --ask mode. Use that (Node main file, acceptable). Actually to stay service-based: `Console.unsafe.log`? prints newline. Just use process.stdout.write via Effect.sync — pragmatic. Alternatively `Console.log(chunk)` each token — noisy newlines. Use stdout.write. **Harness.ts details** — needs imports: Effect, Layer, Console? print inside runSuite uses Console.log — ok. NodeContext/NodeHttpClient imports. Agent/AgentLive, ConfigLive, EventsLive, ToolRegistry+builtins, Mock + MockStep. Also ScenarioOutcome success result typed AgentResult. runScenario: provide layers per scenario — note Effect.provide(effect, layer). ok. detail string: on failure of expectation: "expectation failed"; on agent failure: `renderError(error)`. Also for success-expect false: include final text snippet. Compose detail: ```ts const detail = !pass ? outcome._tag === "Failure" ? renderError(outcome.error) : `final text: ${JSON.stringify(outcome.result.text.slice(0, 120))}, steps: ${outcome.result.steps}` : "ok" ``` ok. runSuite returns Effect printing; sets process.exitCode. defaultScenarios defined in Harness.ts (or Scenarios.ts). Keep in Harness.ts to limit file count. Also `import type { AgentError } from "./Agent.js"`? AgentError exported from Agent.ts: `export type AgentError = LlmError | StepLimitExceeded`. ScenarioOutcome uses it. Also defaultScenarios scenario 2 expects "Recovered" — RepeatToolResult prefix "Recovered: " then tool error content JSON — starts with prefix. ok. Also the Mock "RepeatToolResult" reading last tool message — after unknown tool, transcript has tool message with isError — content includes `"ok":false,"result":"unknown tool..."`. fine. Now — sanity-check the agent loop vs step limit scenario: script 12 × echo tool call. Steps 1..8 execute; at step=9: `if (step > cfg.maxSteps) fail`. Wait, loop structure: for(step=1;;step++){ if(step>maxSteps) fail; ...}. With maxSteps=8: steps 1–8 run (8 LLM calls, 8 tool batches), step 9 fails. Script has 12 entries — cursor 0..7 used; fine. Test scenario 1: step1 → ToolCall clock.now; execTool runs tool (ok) → transcript; step2 → RepeatToolResult → final text "Here it is: {json}". expect: steps===2 && text.startsWith("Here it is:") ✓. Scenario 2: step1 ToolCall unknown tool → runOne fails ToolNotFound → catchAll → ok:false content; step2 RepeatToolResult → text startsWith "Recovered" ✓. Now — one wrinkle: in scenario 1, `agent.run` returns Effect with AgentError possible; we catchAll into outcome. Also `Effect.provide(layersFor(...))` — provides Agent & deps. Since layers built per scenario and scenarios run unbounded concurrently — no shared state. Also harness should maybe *not* include real HTTP for scenarios — builtins include httpGetText but unused. fs unused. Clock used. NodeContext provides FileSystem unused. fine. Also — spans & metrics in scenarios produce logs; pretty logger prints spans? By default the pretty logger logs messages; spans go to tracer (no-op unless enabled? default logger prints span names on end? The default logger includes "fiber" + spans in output? I think spans appear when using logger pretty with `Effect.log`). Harmless. Potential compile nit: `Effect.forEach(scenarios, runScenario, { concurrency: "unbounded" })` — runScenario: (s: Scenario) => Effect — forEach infers. ok. In runScenario, `Effect.catchAll` over gen whose E = AgentError → catchAll (e: AgentError) => Effect.succeed({ _tag: "Failure", error: e } as ScenarioOutcome). Wait — `as ScenarioOutcome` on object literal with _tag "Failure" — ok. But the inner gen returns ScenarioOutcome union — combined type fine. Also `s.expect(outcome)` may throw → wrap with Effect.try + catchAll → false. Compose: ```ts const pass = yield* Effect.try({ try: () => s.expect(outcome), catch: () => false }).pipe(Effect.catchAll(() => Effect.succeed(false))) ``` Effect.try catch returns value? `Effect.try({ try, catch })` — catch: (e) => E (error) — returning false as the *error* is weird. Simpler: ```ts const pass = yield* Effect.sync(() => { try { return s.expect(outcome) } catch { return false } }) ``` sync with try/catch — fine, no async. Now, package versions — write package.json with deps and note to `npm install`. I'll put reasonable carets: effect ^3.13.0; @effect/platform ^0.78.0? pairing... npm will install both latest (satisfying carets independently) — but platform@latest requires effect@latest peer — carets allow. Actually @effect/platform has peerDependency on effect exact-ish range; npm resolves latest platform with latest effect — compatible. If my caret floors are old (3.13 vs latest 3.15), npm picks newest satisfying both carets — platform caret ^0.78 → could pick 0.79 which peers effect ^3.13 → consistent-ish. Risk: caret ranges mismatch combos. Mitigate: instruct `npm install effect @effect/platform @effect/platform-node` (no versions) and let npm pick the coherent latest; package.json then records them. In package.json I'll just list them without versions? Must have versions. I'll put `"effect": "latest"`? ugly but functional for a prototype... Hmm. Better: give `npm i` command in instructions and show package.json with placeholder note? I'll include versions "^3.13" style for effect and matching-ish for platform but add a note: "run `npm i effect @effect/platform @effect/platform-node` to get a mutually compatible set." Simplest robust: dependencies block with `"effect": "^3.13.0", "@effect/platform": "^0.78.0", "@effect/platform-node": "^0.83.0"` — if mismatched, npm ERESOLVE will surface; user can run the install command. Add one-line note. Fine. Actually — thinking again about `@effect/platform-node` version mapping: effect 3.13.x ↔ platform-node 0.81?; 3.14 ↔ 0.82/0.83? Honestly the patch matrix changes weekly; the note approach is right. tsconfig moduleResolution "Bundler" + tsx — works. Add "noEmit": true (tsx runs, tsc typechecks). Also `"strict": true` + effect requires `"skipLibCheck": true` recommended. Add `"experimentalDecorators"`? not needed. Now think about whether `Schema.Schema` type alias usage compiles for `Schema.Schema`: `Schema.Schema` — so `Schema.Schema` = Schema — our Struct schemas: SchemaClass — assignable? SchemaClass extends Schema; for struct of primitives I===A structurally. Yes. JSONSchema.fromSchema(t.parameters) — parameter type `Schema.Schema.All`? accepts. ok. `Schema.parseJson(tool.parameters)` — signature `parseJson(schema: Schema): SchemaClass` — with tool.parameters: Schema fine. Decoded → any. ok. But wait — with `Schema.Schema` where I=any for AnyTool: parseJson(Schema) → fine. decodeArgs returns Effect: ```ts const decodeArgs = (tool: AnyTool, call: ToolCall): Effect.Effect => { const parse = typeof call.arguments === "string" ? Schema.decodeUnknown(Schema.parseJson(tool.parameters)) : Schema.decodeUnknown(tool.parameters) return Effect.mapError(parse(call.arguments ?? {}), (e) => new InvalidToolArgs({ tool: tool.name, detail: e.message })) } ``` Hmm — `Schema.decodeUnknown(schema)` — signature returns `(u: unknown, options?) => Effect`. ok. ParseError.message exists (Error subclass). ok. But `Schema.parseJson(tool.parameters)` — TS overloads: parseJson(schema) — good. Note: `Schema.decodeUnknown(tool.parameters)` where tool.parameters: Schema — decodeUnknown returns Effect — with I=any fine. One more: `Schema.Struct({})` — parameters type `{}`; tool `now: Tool>` — Schema.Struct({}) type: SchemaClass<{}, {}, never> assignable to Schema>? {} vs Record — Record is... {} assignable? Record means no props allowed; {} accepts anything — assignability: Schema, I=Record> vs SchemaClass<{}, {}> — Schema invariant in A? Schema is invariant (A and I both in/out). {} → Record: is `{}` assignable to `Record`? No (Record requires index signature... actually {} type is assignable to Record? hmm). Simpler: type now tool as `Tool<{}>`? `Tool<{ }>`. arguments {} decodes to {}. `Tool

typescript effect