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openspec/archive/2026-05-20-add-broadcast-channel-ask/tasks.md

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+# Tasks — add-broadcast-channel-ask
+
+Sequential. No ticks may be authored retroactively.
+
+## 1. Schema and types
+
+- [ ] 1.1 Extend `src/schemas/messages.ts` — keep the existing `ChannelMessageSchema` shape via
+      `z.discriminatedUnion("type", ...)`-equivalent (or `z.union`) — adding two new variants
+      `AskFrameSchema` (with `correlationId`, `handlerKey`, `payload`, `expiresAt`) and
+      `AskResponseFrameSchema` (with `responseTo`, `handlerKey`, `outcome`, `payload`). Legacy
+      frames (`type` of `tab-join` / `tab-leave` / `heartbeat` / user-defined string + arbitrary
+      `payload`) remain accepted.
+- [ ] 1.2 Add `AskFrame` / `AskResponseFrame` type exports to
+      `src/types/broadcast-channel.types.ts`. Extend `InternalMessageType` union by `"ask"` and
+      `"ask-response"`.
+- [ ] 1.3 Update `src/schemas/messages.test.ts` — add scenarios: accepts well-formed `ask`,
+      accepts well-formed `ask-response`, rejects `ask` missing `correlationId`, rejects
+      `ask-response` missing `responseTo`.
+
+## 2. Error codes
+
+- [ ] 2.1 Extend `BROADCAST_CHANNEL_CODES` in `src/errors/codes.ts` by `ASK_TIMEOUT`,
+      `ASK_NO_RESPONDER`, `ASK_HANDLER_DUPLICATE`.
+- [ ] 2.2 Add three error classes: `BroadcastChannelAskTimeoutError`,
+      `BroadcastChannelAskNoResponderError`, `BroadcastChannelAskHandlerDuplicateError`. Each
+      defaults its message and accepts `BaseOpts`.
+- [ ] 2.3 Update `src/errors/codes.test.ts` — `every code is thrown by a production path` to
+      include the three new errors; registry-shape assertion grows to 7 codes.
+
+## 3. OTel counters
+
+- [ ] 3.1 In `src/otel/metrics.ts` declare module-level counters `askSent`, `askResponded`,
+      `askTimeout`; expose three recorder functions `recordAskSent(key, channelName)`,
+      `recordAskResponded(key, outcome, channelName)`, `recordAskTimeout(key, channelName)`.
+      Update `refreshBroadcastChannelMeters` to re-resolve them.
+- [ ] 3.2 Update `src/otel/metrics.test.ts` — add three scenarios: `ask` sent increments
+      `channel.ask.sent`, response increments `channel.ask.responded` with `outcome` attribute,
+      timeout increments `channel.ask.timeout`.
+
+## 4. `ask` feature module
+
+- [ ] 4.1 `src/ask/ask.ts` — `AskController` class owning the pending-ask registry: keyed by
+      `correlationId`, each entry stores `{ key, resolve, reject, timerHandle, requireResponder,
+      respondersClaimed }`. Exposes `issue(handlerKey, payload, opts)` and `cancelAll(reason)`.
+      Uses injected `Clock`, `Rng`, `TimersLike`.
+- [ ] 4.2 `src/ask/ask.md` — co-located doc ≥200 words covering Purpose / Features / Usage:Basic /
+      Usage:Advanced / API Reference / Implementation Notes.
+- [ ] 4.3 `src/ask/responder.ts` — `AskResponderRegistry` mapping `handlerKey → handler`. Throws
+      `BroadcastChannelAskHandlerDuplicateError` on second registration. Returns a disposer.
+- [ ] 4.4 `src/ask/responder.md` — co-located doc.
+- [ ] 4.5 `src/ask/index.ts` — explicit named re-exports (no `export *`).
+
+## 5. Wire into `TypedBroadcastChannel`
+
+- [ ] 5.1 Add `timers?: TimersLike` to `TypedBroadcastChannelOptions`; default to
+      `{ setTimer: setTimeout, clearTimer: clearTimeout }` (wrapped to satisfy the signature).
+- [ ] 5.2 Construct `AskController` and `AskResponderRegistry` in the constructor.
+- [ ] 5.3 Implement `public ask<TReq, TResp>(handlerKey, payload, opts?): Promise<TResp>`. Calls
+      `recordAskSent`, schedules timeout via `TimersLike.setTimer`, posts `ask` frame through the
+      transport, returns the controller's promise.
+- [ ] 5.4 Implement `public onAsk<TReq, TResp>(handlerKey, handler): () => void`. Throws
+      `ASK_HANDLER_DUPLICATE` on double-registration via `AskResponderRegistry`.
+- [ ] 5.5 Extend `handleIncoming` — on `ask` frame: look up responder, if absent and
+      `requireResponder` would matter, increment `respondersClaimed` (we let the asker's timeout
+      decide). On `ask-response` frame: resolve the matching pending ask, call
+      `recordAskResponded(key, outcome, channelName)`.
+- [ ] 5.6 On `close()`: call `AskController.cancelAll("channel-closed")` rejecting every pending
+      promise with `BroadcastChannelClosedError`.
+
+## 6. Tests
+
+- [ ] 6.1 `src/ask/ask.test.ts` — happy path with two channels sharing a fanout-fake transport;
+      correlation-ID isolation under interleaved asks; FakeClock + fake `TimersLike` drives
+      timeout → `ASK_TIMEOUT`; `requireResponder: true` with no peer answers → `ASK_NO_RESPONDER`;
+      handler-thrown error propagates as `outcome: "error"` and rejects the ask; close() rejects
+      pending asks with `CHANNEL_CLOSED`; default `opts.timeoutMs = 5000`.
+- [ ] 6.2 `src/ask/responder.test.ts` — register / dispose / re-register; duplicate throws
+      `ASK_HANDLER_DUPLICATE`; non-matching `handlerKey` is dropped silently (no asker error, no
+      outbound frame); registered handler receives `(payload, ctx)` and may return a Promise.
+
+## 7. Barrel and exports
+
+- [ ] 7.1 Extend `src/index.ts` with named exports: `BroadcastChannelAskTimeoutError`,
+      `BroadcastChannelAskNoResponderError`, `BroadcastChannelAskHandlerDuplicateError`,
+      `recordAskSent`, `recordAskResponded`, `recordAskTimeout`, `AskFrameSchema`,
+      `AskResponseFrameSchema`, plus the two frame types.
+- [ ] 7.2 Add `./ask/ask`, `./ask/responder` subpath exports in `package.json` for tree-shaking.
+
+## 8. Pre-ship gates
+
+- [ ] 8.1 `bunx biome check src/` — clean (zero diagnostics).
+- [ ] 8.2 `bunx turbo lint typecheck test --filter=@suaveplan/broadcast-channel` — green.
+- [ ] 8.3 `bunx turbo test:coverage --filter=@suaveplan/broadcast-channel` — 100/100/100/100.
+- [ ] 8.4 `bun scripts/openspec-conformance.ts @suaveplan/broadcast-channel` — zero errors.
+- [ ] 8.5 `bunx turbo build --filter=@suaveplan/broadcast-channel` — green.
+
+## 9. Archive
+
+- [ ] 9.1 Fold `specs/broadcast-channel/spec.md` (`## ADDED Requirements` block) into
+      `openspec/specs/broadcast-channel/spec.md`.
+- [ ] 9.2 Move `openspec/changes/add-broadcast-channel-ask` →
+      `openspec/archive/2026-05-20-add-broadcast-channel-ask`.