refactor(chat): route browser chat through one runtime (P3 Slice-Zero Task 5) (#1172)

Co-authored-by: shaggy <[email protected]>

apps/web/src/spa/chat/use-chat-connection.spec.tsx

@@ -21,6 +21,7 @@ vi.mock('@/lib/socket', () => ({
   destroySocket: destroySocketMock,
 }));
 
+import type { ChatSendProtocol, HarnessSelection } from '@mosaicstack/types';
 import { useChatConnection, type ChatConnectionValue } from './use-chat-connection';
 
 let fake: ReturnType<typeof createFakeChatSocket>;
@@ -33,6 +34,126 @@ function Harness(): null {
   return null;
 }
 
+/**
+ * Task Five, Step Two (web send path) red-first support. These probe the FUTURE
+ * pi-rpc send contract against the CURRENT implementation, so the desired API is
+ * expressed here as a localized cast — production types stay untouched until Step
+ * Three. The reds fail on behaviour (legacy `message` emitted instead of
+ * `turn:send`; no nested selection; no idempotency key; void return; no
+ * conversation-id gating), never on a missing module or type.
+ */
+interface HarnessTurnSendInput {
+  readonly content: string;
+  readonly selection: HarnessSelection;
+}
+type HarnessSendMessage = (input: HarnessTurnSendInput) => boolean;
+
+function harnessSend(): HarnessSendMessage {
+  return latest?.actions.sendMessage as unknown as HarnessSendMessage;
+}
+
+/**
+ * Task Five MAJOR-1 (browser send-protocol negotiation) support. The Gateway
+ * advertises how this connection may send via a server-to-client-only
+ * `chat:send-capability` (already part of the typed `ServerToClientEvents`
+ * contract, so this uses the fake's typed `serverEmit` — no cast); the hook
+ * holds the advertised protocol and routes `sendMessage` through an exhaustive
+ * switch on it, never inferring it from conversation/selection. When no listener
+ * is registered yet (CURRENT impl), the emit is an inert no-op, so the reds
+ * below fail on BEHAVIOUR — the current send path still infers a protocol and
+ * emits regardless of any advertisement — not on a missing module or type.
+ */
+function advertiseCapability(protocol: ChatSendProtocol, connectionId: string): void {
+  fake.serverEmit('chat:send-capability', { protocol, connectionId });
+}
+
+/**
+ * Install a controllable `crypto.randomUUID` on the global crypto object and
+ * return a restore fn. Uses defineProperty on the instance so it works whether
+ * or not the native method is configurable (it lives on the prototype, so an own
+ * property simply shadows it).
+ */
+function installRandomUUID(fn: () => string): () => void {
+  const g = globalThis as { crypto?: { randomUUID?: () => string } };
+  if (!g.crypto) {
+    Object.defineProperty(g, 'crypto', { configurable: true, writable: true, value: {} });
+  }
+  const cryptoObj = g.crypto as { randomUUID?: () => string };
+  const original = Object.getOwnPropertyDescriptor(cryptoObj, 'randomUUID');
+  Object.defineProperty(cryptoObj, 'randomUUID', {
+    configurable: true,
+    writable: true,
+    value: fn,
+  });
+  return () => {
+    if (original) {
+      Object.defineProperty(cryptoObj, 'randomUUID', original);
+    } else {
+      Reflect.deleteProperty(cryptoObj, 'randomUUID');
+    }
+  };
+}
+
+/**
+ * Force `crypto.randomUUID` to read as ABSENT by shadowing it with an own
+ * `undefined` property. The native method lives on `Crypto.prototype`, so a
+ * bare delete of the (non-existent) own property would leave the inherited
+ * method visible — the shadow is what actually makes the call site see no
+ * secure generator. Returns a restore fn.
+ */
+function removeRandomUUID(): () => void {
+  const g = globalThis as { crypto?: { randomUUID?: () => string } };
+  if (!g.crypto) {
+    Object.defineProperty(g, 'crypto', { configurable: true, writable: true, value: {} });
+  }
+  const cryptoObj = g.crypto as { randomUUID?: () => string };
+  const original = Object.getOwnPropertyDescriptor(cryptoObj, 'randomUUID');
+  Object.defineProperty(cryptoObj, 'randomUUID', {
+    configurable: true,
+    writable: true,
+    value: undefined,
+  });
+  return () => {
+    if (original) {
+      Object.defineProperty(cryptoObj, 'randomUUID', original);
+    } else {
+      Reflect.deleteProperty(cryptoObj, 'randomUUID');
+    }
+  };
+}
+
+/**
+ * Task Five, Step Two group 4/5 support — the FUTURE `turn:ack` receipt surface
+ * and the FUTURE fixed idempotency/rejection notice, expressed as a localized
+ * read-only view over `state`. Production `ChatConnectionState` gains
+ * `turnReceipt` at Step Three; the cast keeps production types untouched until
+ * then, so a success assertion against it fails on BEHAVIOUR (no turn:ack
+ * handler runs), never on a missing module. `error` already exists on state.
+ */
+interface HarnessTurnReceiptView {
+  readonly idempotencyKey: string;
+  readonly receiptId: string;
+  readonly selection: HarnessSelection;
+}
+interface HarnessTurnStateView {
+  readonly turnReceipt: HarnessTurnReceiptView | null | undefined;
+  readonly error: string | null;
+}
+function harnessTurnState(): HarnessTurnStateView {
+  return latest?.state as unknown as HarnessTurnStateView;
+}
+
+/**
+ * Emit a server `turn:ack` the CURRENT hook has no listener for — a safe no-op
+ * today (the fake iterates an empty handler set), so the group-4 reds fail
+ * because nothing is surfaced, not because this throws. The event name is cast
+ * past the compile-time `ServerToClientEvents` contract exactly as the
+ * `turn:send` client cast is; the typed event map lands at Step Three.
+ */
+function serverEmitTurnAck(payload: unknown): void {
+  fake.serverEmitRaw('turn:ack' as unknown as Parameters<typeof fake.serverEmitRaw>[0], payload);
+}
+
 beforeAll(() => {
   Object.defineProperty(globalThis, 'IS_REACT_ACT_ENVIRONMENT', {
     configurable: true,
@@ -67,6 +188,20 @@ afterEach(async () => {
 });
 
 describe('useChatConnection', () => {
+  // Task Five MAJOR-1: the send path is PROTOCOL-driven — `sendMessage` routes
+  // only on the negotiated `chat:send-capability`, never on inferred
+  // conversation/selection state. These pre-existing cases exercise the legacy
+  // `message` branch, so the connection is advertised `legacy-message` once here
+  // (server-to-client, for this exact socket id) after the mount registers its
+  // listener. Sub-describes that need the pi turn-runtime reset the generation
+  // and re-advertise `turn-send`; the capability describe resets to the
+  // unadvertised `unavailable` baseline and drives the protocol itself.
+  beforeEach(async () => {
+    await act(async () => {
+      advertiseCapability('legacy-message', fake.socket.id);
+    });
+  });
+
   it('establishes the active conversation from the first message:ack when message omitted conversationId', async () => {
     await act(async () => {
       fake.serverEmit('message:ack', { conversationId: 'c1', messageId: 'm1' });
@@ -344,7 +479,10 @@ describe('useChatConnection', () => {
 
   it('sendMessage emits optional conversationId/provider/modelId and appends an optimistic user turn', async () => {
     await act(async () => {
-      latest?.actions.sendMessage({ content: 'hello', provider: 'anthropic', modelId: 'claude' });
+      latest?.actions.sendMessage({
+        content: 'hello',
+        selection: { harnessId: 'pi', providerId: 'anthropic', modelId: 'claude' },
+      });
     });
 
     expect(fake.emitted).toContainEqual({
@@ -373,6 +511,408 @@ describe('useChatConnection', () => {
     });
   });
 
+  describe('turn:send harness routing (Task Five, Step Two red-first)', () => {
+    const selection: HarnessSelection = {
+      harnessId: 'pi',
+      providerId: 'anthropic',
+      modelId: 'claude',
+    };
+    const UUID = 'aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa';
+
+    // The pi turn-runtime routes sends through `turn:send`. Reset the generation
+    // (clearing the outer `legacy-message` advertisement + first-wins lock) and
+    // advertise `turn-send` for this exact connection, so every send below takes
+    // the turn-runtime branch.
+    beforeEach(async () => {
+      await act(async () => {
+        fake.simulateReconnect();
+      });
+      await act(async () => {
+        advertiseCapability('turn-send', fake.socket.id);
+      });
+    });
+
+    async function establishConversation(): Promise<void> {
+      await act(async () => {
+        fake.serverEmit('message:ack', { conversationId: 'c1', messageId: 'm1' });
+      });
+    }
+
+    it('emits a single turn:send with the nested selection tuple and a UUID idempotencyKey — never the legacy message event', async () => {
+      const restore = installRandomUUID(() => UUID);
+      try {
+        await establishConversation();
+        await act(async () => {
+          harnessSend()({ content: 'hello', selection });
+        });
+      } finally {
+        restore();
+      }
+
+      const sends = fake.emitted.filter((e) => e.event === 'turn:send');
+      expect(sends).toHaveLength(1);
+      expect(sends[0]?.payload).toEqual({
+        conversationId: 'c1',
+        content: 'hello',
+        selection,
+        idempotencyKey: UUID,
+      });
+      // The pi-rpc sender must not fall back to the embedded `message` event.
+      expect(fake.emitted.some((e) => e.event === 'message')).toBe(false);
+    });
+
+    it('generates the idempotencyKey with exactly one crypto.randomUUID() call per accepted send', async () => {
+      const gen = vi.fn(() => UUID);
+      const restore = installRandomUUID(gen);
+      try {
+        await establishConversation();
+        await act(async () => {
+          harnessSend()({ content: 'first', selection });
+        });
+        await act(async () => {
+          harnessSend()({ content: 'second', selection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(gen).toHaveBeenCalledTimes(2);
+      const keys = fake.emitted
+        .filter((e) => e.event === 'turn:send')
+        .map((e) => (e.payload as { idempotencyKey: string }).idempotencyKey);
+      expect(keys).toEqual([UUID, UUID]);
+    });
+
+    it('does not send before an active conversation id exists (no first-send auto-create)', async () => {
+      const restore = installRandomUUID(() => UUID);
+      let returned: boolean | undefined;
+      try {
+        await act(async () => {
+          returned = harnessSend()({ content: 'too early', selection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(returned).toBe(false);
+      expect(fake.emitted.some((e) => e.event === 'turn:send')).toBe(false);
+      expect(fake.emitted.some((e) => e.event === 'message')).toBe(false);
+      // Nothing optimistically appended when the send is refused.
+      expect(latest?.state.messages.some((m) => m.text === 'too early')).toBe(false);
+    });
+
+    it('returns true when it emits and false when the send is refused', async () => {
+      const restore = installRandomUUID(() => UUID);
+      let refusedEarly: boolean | undefined;
+      let acceptedAfter: boolean | undefined;
+      try {
+        await act(async () => {
+          refusedEarly = harnessSend()({ content: 'early', selection });
+        });
+        await establishConversation();
+        await act(async () => {
+          acceptedAfter = harnessSend()({ content: 'now', selection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(refusedEarly).toBe(false);
+      expect(acceptedAfter).toBe(true);
+    });
+
+    it('when secure UUID generation throws: emits nothing, appends nothing, releases the lock, and a later send succeeds', async () => {
+      await establishConversation();
+
+      const failing = installRandomUUID(() => {
+        throw new Error('secure random unavailable');
+      });
+      let firstReturn: boolean | undefined;
+      try {
+        await act(async () => {
+          firstReturn = harnessSend()({ content: 'blocked', selection });
+        });
+      } finally {
+        failing();
+      }
+
+      expect(firstReturn).toBe(false);
+      expect(fake.emitted.some((e) => e.event === 'turn:send')).toBe(false);
+      expect(latest?.state.messages.some((m) => m.text === 'blocked')).toBe(false);
+
+      // The send lock must have been released, so a subsequent valid send works.
+      const restore = installRandomUUID(() => UUID);
+      let secondReturn: boolean | undefined;
+      try {
+        await act(async () => {
+          secondReturn = harnessSend()({ content: 'retry', selection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(secondReturn).toBe(true);
+      expect(fake.emitted.some((e) => e.event === 'turn:send')).toBe(true);
+    });
+  });
+
+  describe('turn:ack receipt + rejection contract (Task Five, Step Two group 4)', () => {
+    const selection: HarnessSelection = {
+      harnessId: 'pi',
+      providerId: 'anthropic',
+      modelId: 'claude',
+    };
+    const UUID = 'aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa';
+
+    // turn:ack is the receipt for a `turn:send`, so these establish under the pi
+    // turn-runtime: reset the generation (clearing the outer `legacy-message`
+    // advertisement + lock) and advertise `turn-send` for this connection.
+    beforeEach(async () => {
+      await act(async () => {
+        fake.simulateReconnect();
+      });
+      await act(async () => {
+        advertiseCapability('turn-send', fake.socket.id);
+      });
+    });
+
+    // Establish the conversation and send one accepted turn under a controlled
+    // idempotency key. Returns the crypto restore fn so callers unwind it.
+    async function establishAndSend(): Promise<() => void> {
+      const restore = installRandomUUID(() => UUID);
+      await act(async () => {
+        fake.serverEmit('message:ack', { conversationId: 'c1', messageId: 'm1' });
+      });
+      await act(async () => {
+        harnessSend()({ content: 'hello', selection });
+      });
+      return restore;
+    }
+
+    it('surfaces a turn:ack receipt echoing the exact idempotencyKey, server receiptId, and requested selection tuple', async () => {
+      const restore = await establishAndSend();
+      try {
+        await act(async () => {
+          serverEmitTurnAck({
+            conversationId: 'c1',
+            idempotencyKey: UUID,
+            receiptId: 'r1',
+            selection,
+          });
+        });
+      } finally {
+        restore();
+      }
+
+      // RED anchor: no turn:ack handler exists, so nothing is recorded. Green
+      // only when Step Three echoes the exact tuple back into state — never a
+      // substituted or fabricated one.
+      expect(harnessTurnState().turnReceipt).toEqual({
+        idempotencyKey: UUID,
+        receiptId: 'r1',
+        selection,
+      });
+    });
+
+    it('on a rejected turn:ack surfaces a visible safe notice, never the raw internal error, and fabricates no receipt tuple', async () => {
+      const restore = await establishAndSend();
+      try {
+        await act(async () => {
+          serverEmitTurnAck({
+            conversationId: 'c1',
+            idempotencyKey: UUID,
+            ok: false,
+            code: 'runtime_unsupported',
+            error: 'ADAPTER_BOOM internal stack: pi adapter unavailable at 0xdeadbeef',
+          });
+        });
+      } finally {
+        restore();
+      }
+
+      // RED anchor: a rejected ack must surface a visible notice; today no
+      // handler runs, so state.error stays null.
+      expect(harnessTurnState().error).toBeTruthy();
+      // The raw internal exception text must never reach the browser surface.
+      expect(harnessTurnState().error ?? '').not.toContain('ADAPTER_BOOM');
+      expect(harnessTurnState().error ?? '').not.toContain('0xdeadbeef');
+      // A rejection must not fabricate a success receipt tuple.
+      expect(harnessTurnState().turnReceipt ?? null).toBeNull();
+    });
+
+    it('uses one fixed safe rejection notice regardless of the internal cause (frozen union, not a passthrough)', async () => {
+      const firstRestore = await establishAndSend();
+      try {
+        await act(async () => {
+          serverEmitTurnAck({
+            conversationId: 'c1',
+            idempotencyKey: UUID,
+            ok: false,
+            code: 'runtime_unsupported',
+            error: 'cause-ALPHA adapter_unavailable',
+          });
+        });
+      } finally {
+        firstRestore();
+      }
+      const firstNotice = harnessTurnState().error;
+
+      // A fresh turn on the same conversation, rejected for a DIFFERENT internal
+      // reason, must surface the identical fixed notice.
+      const secondRestore = installRandomUUID(() => UUID);
+      try {
+        await act(async () => {
+          harnessSend()({ content: 'again', selection });
+        });
+        await act(async () => {
+          serverEmitTurnAck({
+            conversationId: 'c1',
+            idempotencyKey: UUID,
+            ok: false,
+            code: 'runtime_unsupported',
+            error: 'cause-BRAVO conversation_service_unavailable',
+          });
+        });
+      } finally {
+        secondRestore();
+      }
+      const secondNotice = harnessTurnState().error;
+
+      // RED anchor: both are null today; green requires a single frozen safe
+      // string surfaced for both distinct internal causes.
+      expect(firstNotice).toBeTruthy();
+      expect(secondNotice).toBeTruthy();
+      expect(firstNotice).toBe(secondNotice);
+      expect(firstNotice ?? '').not.toContain('ALPHA');
+      expect(secondNotice ?? '').not.toContain('BRAVO');
+    });
+  });
+
+  describe('idempotency-key failure semantics (Task Five, Step Two group 5)', () => {
+    const selection: HarnessSelection = {
+      harnessId: 'pi',
+      providerId: 'anthropic',
+      modelId: 'claude',
+    };
+    const UUID_A = '11111111-1111-4111-8111-111111111111';
+    const UUID_B = '22222222-2222-4222-9222-222222222222';
+    const UUID_V4 = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;
+
+    // The idempotency key is minted only on the pi turn-runtime `turn:send`
+    // branch: reset the generation (clearing the outer `legacy-message`
+    // advertisement + lock) and advertise `turn-send` for this connection.
+    beforeEach(async () => {
+      await act(async () => {
+        fake.simulateReconnect();
+      });
+      await act(async () => {
+        advertiseCapability('turn-send', fake.socket.id);
+      });
+    });
+
+    async function establish(): Promise<void> {
+      await act(async () => {
+        fake.serverEmit('message:ack', { conversationId: 'c1', messageId: 'm1' });
+      });
+    }
+
+    it('mints a DISTINCT UUID-v4 idempotencyKey for each of two accepted turns — a key is never reused across turns', async () => {
+      const keys = [UUID_A, UUID_B];
+      let call = 0;
+      const restore = installRandomUUID(() => keys[call++] ?? UUID_A);
+      try {
+        await establish();
+        await act(async () => {
+          harnessSend()({ content: 'first', selection });
+        });
+        await act(async () => {
+          harnessSend()({ content: 'second', selection });
+        });
+      } finally {
+        restore();
+      }
+
+      const sent = fake.emitted
+        .filter((e) => e.event === 'turn:send')
+        .map((e) => (e.payload as { idempotencyKey: string }).idempotencyKey);
+      // RED anchor: current sendMessage emits the legacy `message`, so no
+      // turn:send keys exist at all.
+      expect(sent).toHaveLength(2);
+      expect(sent[0]).toMatch(UUID_V4);
+      expect(sent[1]).toMatch(UUID_V4);
+      expect(sent[0]).not.toBe(sent[1]);
+    });
+
+    it('when crypto.randomUUID is ABSENT: surfaces a visible fixed idempotency-unavailable notice, emits nothing, appends nothing, releases the lock synchronously, and a later valid send succeeds', async () => {
+      await establish();
+
+      const restoreCrypto = removeRandomUUID();
+      let firstReturn: boolean | undefined;
+      try {
+        await act(async () => {
+          firstReturn = harnessSend()({ content: 'no-secure-random', selection });
+        });
+      } finally {
+        restoreCrypto();
+      }
+
+      // RED anchors: a refused send returns false and surfaces a visible notice.
+      expect(firstReturn).toBe(false);
+      expect(harnessTurnState().error).toBeTruthy();
+      expect(fake.emitted.some((e) => e.event === 'turn:send')).toBe(false);
+      expect(latest?.state.messages.some((m) => m.text === 'no-secure-random')).toBe(false);
+
+      // The lock released synchronously (no server event needed): a later valid
+      // send goes through.
+      const restore = installRandomUUID(() => UUID_A);
+      let secondReturn: boolean | undefined;
+      try {
+        await act(async () => {
+          secondReturn = harnessSend()({ content: 'recovered', selection });
+        });
+      } finally {
+        restore();
+      }
+      expect(secondReturn).toBe(true);
+      expect(fake.emitted.some((e) => e.event === 'turn:send')).toBe(true);
+    });
+
+    it('surfaces the SAME fixed idempotency-unavailable notice whether randomUUID is absent or throws, never leaking the thrown message', async () => {
+      // Case 1: absent.
+      await establish();
+      const restoreAbsent = removeRandomUUID();
+      try {
+        await act(async () => {
+          harnessSend()({ content: 'absent', selection });
+        });
+      } finally {
+        restoreAbsent();
+      }
+      const absentNotice = harnessTurnState().error;
+
+      // Case 2: throws with a distinctive internal message.
+      const failing = installRandomUUID(() => {
+        throw new Error('SECURE_RANDOM_BOOM entropy pool drained');
+      });
+      try {
+        await act(async () => {
+          harnessSend()({ content: 'throws', selection });
+        });
+      } finally {
+        failing();
+      }
+      const throwNotice = harnessTurnState().error;
+
+      // RED anchor: both are null today.
+      expect(absentNotice).toBeTruthy();
+      expect(throwNotice).toBeTruthy();
+      expect(absentNotice).toBe(throwNotice);
+      // The thrown internal detail must never reach the browser surface.
+      expect(throwNotice ?? '').not.toContain('SECURE_RANDOM_BOOM');
+      expect(throwNotice ?? '').not.toContain('entropy pool');
+    });
+  });
+
   it('abort emits abort with the active conversationId', async () => {
     await act(async () => {
       fake.serverEmit('message:ack', { conversationId: 'c1', messageId: 'm1' });
@@ -684,7 +1224,16 @@ describe('useChatConnection', () => {
     expect(latest?.state.approvalRequestPending).toBe(false);
 
     // The send lock must also be released — a subsequent sendMessage after
-    // reconnect must not be permanently blocked by the interrupted turn.
+    // reconnect must not be permanently blocked by the interrupted turn. The
+    // disconnect also voids the negotiated send protocol (MAJOR-1), so model the
+    // reconnect handshake — the socket reconnects and the server re-advertises
+    // how this connection may send — before probing the released lock.
+    await act(async () => {
+      fake.simulateReconnect();
+    });
+    await act(async () => {
+      advertiseCapability('legacy-message', fake.socket.id);
+    });
     await act(async () => {
       latest?.actions.sendMessage({ content: 'after reconnect' });
     });
@@ -1665,4 +2214,319 @@ describe('useChatConnection', () => {
     }
     expect(destroySocketMock).toHaveBeenCalledOnce();
   });
+
+  describe('chat:send-capability protocol negotiation (Task Five MAJOR-1, red-first)', () => {
+    const capSelection: HarnessSelection = {
+      harnessId: 'pi',
+      providerId: 'anthropic',
+      modelId: 'claude',
+    };
+    const UUID = 'bbbbbbbb-bbbb-4bbb-8bbb-bbbbbbbbbbbb';
+    // The one fixed, safe user-facing notice the hook must surface (code
+    // `send_protocol_unavailable`) when a send is attempted on a connection whose
+    // advertised protocol is `unavailable`/unknown/absent. Contract-frozen string.
+    const UNAVAILABLE_NOTICE = 'Chat sending is unavailable on this connection.';
+
+    // These tests each drive the protocol negotiation themselves, so they must
+    // start from a clean, unadvertised generation. Reconnect resets protocolRef
+    // to `unavailable` and clears the outer `legacy-message` first-wins lock
+    // WITHOUT advertising — no client emit, so `fake.emitted` stays empty and the
+    // "starts unavailable" premise holds.
+    beforeEach(async () => {
+      await act(async () => {
+        fake.simulateReconnect();
+      });
+    });
+
+    async function establishConversation(): Promise<void> {
+      await act(async () => {
+        fake.serverEmit('message:ack', { conversationId: 'c1', messageId: 'm1' });
+      });
+    }
+
+    function connectCalls(): number {
+      return (fake.socket.connect as unknown as { mock: { calls: unknown[] } }).mock.calls.length;
+    }
+
+    it('starts with no advertised protocol: a send is refused, emits nothing, mints no key, and surfaces the fixed unavailable notice', async () => {
+      // No `chat:send-capability` has arrived, so the connection has not been told
+      // it may send at all. The current impl infers "selection + no conversation +
+      // no flat provider/model → return false" but SURFACES NOTHING — the red is
+      // that the fixed `send_protocol_unavailable` notice is never set.
+      let uuidCalls = 0;
+      const restore = installRandomUUID(() => {
+        uuidCalls += 1;
+        return UUID;
+      });
+      let returned: boolean | undefined;
+      try {
+        await act(async () => {
+          returned = harnessSend()({ content: 'hi', selection: capSelection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(returned).toBe(false);
+      expect(fake.emitted).toHaveLength(0);
+      expect(latest?.state.error).toBe(UNAVAILABLE_NOTICE);
+      // The test's name promises "mints no key": the unavailable branch must not
+      // reach the idempotency mint at all. Without this assertion a defect that
+      // mints a key before refusing survives.
+      expect(uuidCalls).toBe(0);
+      // ...and no user content may be optimistically appended on refusal.
+      expect(latest?.state.messages.some((m) => m.text === 'hi')).toBe(false);
+    });
+
+    it('legacy-message advertised overrides conversation-inference: an established conversation still routes the legacy message event, never turn:send', async () => {
+      // Same inputs the inference impl routes to `turn:send` (selection + active
+      // conversation). The advertised protocol is authoritative: it must emit the
+      // legacy `message` event instead. Red: current impl emits turn:send.
+      const restore = installRandomUUID(() => UUID);
+      try {
+        await establishConversation();
+        await act(async () => {
+          advertiseCapability('legacy-message', fake.socket.id);
+        });
+        await act(async () => {
+          harnessSend()({ content: 'hi', selection: capSelection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(fake.emitted.filter((e) => e.event === 'turn:send')).toHaveLength(0);
+      expect(fake.emitted).toContainEqual({
+        event: 'message',
+        payload: { conversationId: 'c1', content: 'hi', provider: 'anthropic', modelId: 'claude' },
+      });
+    });
+
+    it('legacy-message advertised with no conversation: derives provider/model from the selection tuple and emits one message', async () => {
+      // The flat provider/modelId caller inputs are gone; the legacy branch must
+      // source them from the confirmed persisted selection. Red: current impl
+      // refuses a bare harness send (selection + no flat fields → return false).
+      let returned: boolean | undefined;
+      const restore = installRandomUUID(() => UUID);
+      try {
+        await act(async () => {
+          advertiseCapability('legacy-message', fake.socket.id);
+        });
+        await act(async () => {
+          returned = harnessSend()({ content: 'first', selection: capSelection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(returned).toBe(true);
+      expect(fake.emitted).toContainEqual({
+        event: 'message',
+        payload: {
+          conversationId: undefined,
+          content: 'first',
+          provider: 'anthropic',
+          modelId: 'claude',
+        },
+      });
+      expect(fake.emitted.some((e) => e.event === 'turn:send')).toBe(false);
+    });
+
+    it('unavailable advertised: refuses even with an active conversation and selection, emits nothing, surfaces the fixed notice', async () => {
+      // Red: current impl ignores the advertisement and emits turn:send.
+      let uuidCalls = 0;
+      const restore = installRandomUUID(() => {
+        uuidCalls += 1;
+        return UUID;
+      });
+      let returned: boolean | undefined;
+      try {
+        await establishConversation();
+        await act(async () => {
+          advertiseCapability('unavailable', fake.socket.id);
+        });
+        await act(async () => {
+          returned = harnessSend()({ content: 'nope', selection: capSelection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(returned).toBe(false);
+      expect(fake.emitted).toHaveLength(0);
+      expect(latest?.state.error).toBe(UNAVAILABLE_NOTICE);
+      // Refusal must not optimistically append the user's turn to the transcript
+      // (a distinct leak from the emit): the unavailable branch appends nothing.
+      expect(latest?.state.messages.some((m) => m.text === 'nope')).toBe(false);
+      // ...and must not mint an idempotency key on the refused path.
+      expect(uuidCalls).toBe(0);
+    });
+
+    it('ignores an advertisement whose connectionId does not match the socket id: protocol stays unavailable and the send is refused', async () => {
+      // A capability minted for a different (stale/foreign) connection must never
+      // arm this one. Red: current impl has no connection-id gate and emits
+      // turn:send off the inferred path.
+      const restore = installRandomUUID(() => UUID);
+      let returned: boolean | undefined;
+      try {
+        await establishConversation();
+        await act(async () => {
+          advertiseCapability('legacy-message', 'a-different-connection');
+        });
+        await act(async () => {
+          returned = harnessSend()({ content: 'spoof', selection: capSelection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(returned).toBe(false);
+      expect(fake.emitted).toHaveLength(0);
+      expect(latest?.state.error).toBe(UNAVAILABLE_NOTICE);
+    });
+
+    it('accepts only the first advertisement for the generation: a later conflicting protocol is ignored', async () => {
+      // legacy-message wins; the subsequent turn-send is a replay/conflict and is
+      // dropped. Red: current impl ignores both and infers turn:send.
+      const restore = installRandomUUID(() => UUID);
+      try {
+        await establishConversation();
+        await act(async () => {
+          advertiseCapability('legacy-message', fake.socket.id);
+        });
+        await act(async () => {
+          advertiseCapability('turn-send', fake.socket.id);
+        });
+        await act(async () => {
+          harnessSend()({ content: 'hi', selection: capSelection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(fake.emitted.filter((e) => e.event === 'turn:send')).toHaveLength(0);
+      expect(fake.emitted).toContainEqual({
+        event: 'message',
+        payload: { conversationId: 'c1', content: 'hi', provider: 'anthropic', modelId: 'claude' },
+      });
+    });
+
+    it('resets to unavailable on disconnect: a later send is refused and never reconnects the socket', async () => {
+      // Disconnect voids the advertised protocol for the generation. The send must
+      // refuse and MUST NOT call socket.connect() to force a reconnection. Red:
+      // current impl keeps the conversation, infers turn:send, and its turn:send
+      // branch calls socket.connect() when the socket is disconnected.
+      const restore = installRandomUUID(() => UUID);
+      let returned: boolean | undefined;
+      let connectsDuringSend = 0;
+      try {
+        await establishConversation();
+        await act(async () => {
+          advertiseCapability('legacy-message', fake.socket.id);
+        });
+        await act(async () => {
+          fake.simulateDisconnect();
+        });
+        const before = connectCalls();
+        await act(async () => {
+          returned = harnessSend()({ content: 'after-drop', selection: capSelection });
+        });
+        connectsDuringSend = connectCalls() - before;
+      } finally {
+        restore();
+      }
+
+      expect(returned).toBe(false);
+      expect(fake.emitted).toHaveLength(0);
+      expect(latest?.state.error).toBe(UNAVAILABLE_NOTICE);
+      expect(connectsDuringSend).toBe(0);
+    });
+
+    it('resets on reconnect to a fresh generation: refuses until re-advertised, then honors the new advertisement', async () => {
+      // A reconnect mints a new Socket.id and a new generation; the prior
+      // advertisement (bound to the old id) is stale and must not carry over. The
+      // hook only trusts a fresh advertisement for the new connection. Red:
+      // current impl has no connect listener and keeps inferring turn:send.
+      const restore = installRandomUUID(() => UUID);
+      let refusedAfterReconnect: boolean | undefined;
+      try {
+        await establishConversation();
+        await act(async () => {
+          advertiseCapability('legacy-message', fake.socket.id);
+        });
+        await act(async () => {
+          fake.simulateReconnect('socket-b');
+        });
+        await act(async () => {
+          refusedAfterReconnect = harnessSend()({ content: 'stale', selection: capSelection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(refusedAfterReconnect).toBe(false);
+      expect(fake.emitted).toHaveLength(0);
+      expect(latest?.state.error).toBe(UNAVAILABLE_NOTICE);
+
+      // A fresh advertisement for the reconnected id (socket-b) re-arms sending.
+      const restore2 = installRandomUUID(() => UUID);
+      try {
+        await act(async () => {
+          advertiseCapability('legacy-message', 'socket-b');
+        });
+        await act(async () => {
+          harnessSend()({ content: 'welcome-back', selection: capSelection });
+        });
+      } finally {
+        restore2();
+      }
+
+      expect(fake.emitted).toContainEqual({
+        event: 'message',
+        payload: {
+          conversationId: 'c1',
+          content: 'welcome-back',
+          provider: 'anthropic',
+          modelId: 'claude',
+        },
+      });
+      expect(fake.emitted.some((e) => e.event === 'turn:send')).toBe(false);
+    });
+
+    it('routes on the synchronous protocol ref, not the batched reducer mirror: an advertisement and a send in the SAME tick still route by the just-advertised protocol', async () => {
+      // An advertisement lands and a send is issued within one synchronous tick,
+      // before React commits the reducer's `sendProtocol` mirror. The send is
+      // captured from the pre-advertisement render, so its closed-over reducer
+      // state still reads `sendProtocol === 'unavailable'`; the capability
+      // handler, however, has already set the synchronous `protocolRef` to
+      // `legacy-message`. The hook must route on that ref. Red (against a
+      // stale-mirror routing that reads `state.sendProtocol`): the send reads the
+      // pre-advertisement `unavailable` and refuses instead of emitting `message`.
+      const restore = installRandomUUID(() => UUID);
+      try {
+        await act(async () => {
+          // Bound to the CURRENT (pre-advertisement) render — its closure still
+          // sees the reset `unavailable` mirror even after the advert dispatches.
+          const sendBeforeCommit = harnessSend();
+          advertiseCapability('legacy-message', fake.socket.id);
+          // Same tick, no await: React has not committed the new mirror yet, so
+          // only `protocolRef` reflects `legacy-message`.
+          sendBeforeCommit({ content: 'same-tick', selection: capSelection });
+        });
+      } finally {
+        restore();
+      }
+
+      expect(fake.emitted).toContainEqual({
+        event: 'message',
+        payload: {
+          conversationId: undefined,
+          content: 'same-tick',
+          provider: 'anthropic',
+          modelId: 'claude',
+        },
+      });
+      expect(fake.emitted.some((e) => e.event === 'turn:send')).toBe(false);
+    });
+  });
 });