feat(chat): unify session gateway with stable IDs and a single WS protocol

The frontend previously juggled placeholder IDs, provider-native IDs, and session_created handoffs, which caused race conditions and provider-specific branching. This introduces app-allocated session IDs, a chat run registry with event replay, delta sidebar updates, and one kind-based websocket contract so the UI can treat every provider the same while JSONL remains the source of truth.

server/modules/websocket/services/chat-run-registry.service.ts

@@ -0,0 +1,257 @@
+import { sessionsDb } from '@/modules/database/index.js';
+import { ChatSessionWriter } from '@/modules/websocket/services/chat-session-writer.service.js';
+import type {
+  LLMProvider,
+  NormalizedMessage,
+  RealtimeClientConnection,
+} from '@/shared/types.js';
+
+type ChatRunStatus = 'running' | 'completed';
+
+/**
+ * One live (or recently finished) provider run for a single app session.
+ *
+ * State notes — why each mutable field is essential:
+ * - `providerSessionId`: the provider-native id captured mid-run. The abort
+ *   handler needs it to address the provider runtime, and the DB mapping is
+ *   written from it so history/resume work after the run.
+ * - `status`: drives `chat_subscribed.isProcessing`, prevents double sends
+ *   into the same session, and guards the synthetic-complete fallback in the
+ *   chat handler (only emitted when a runtime died without completing).
+ * - `lastSeq` / `events`: the per-run event log. Every live event gets a
+ *   monotonically increasing `seq` and is buffered so a reconnecting client
+ *   can replay exactly the events it missed via `chat.subscribe`.
+ */
+type ChatRun = {
+  appSessionId: string;
+  provider: LLMProvider;
+  providerSessionId: string | null;
+  status: ChatRunStatus;
+  lastSeq: number;
+  events: NormalizedMessage[];
+  writer: ChatSessionWriter;
+  startedAt: number;
+  completedAt: number | null;
+};
+
+/**
+ * How long a completed run stays available for replay. Covers the window
+ * between a run finishing and the client refreshing history over REST (for
+ * example when the browser tab was asleep while the run completed).
+ */
+const COMPLETED_RUN_RETENTION_MS = 5 * 60 * 1000;
+
+/**
+ * Upper bound on buffered events per run so a very long tool-heavy run cannot
+ * grow memory unbounded. When exceeded, the oldest events are dropped —
+ * a reconnecting client whose `lastSeq` predates the buffer falls back to a
+ * REST history refresh, which is always the authoritative source.
+ */
+const MAX_BUFFERED_EVENTS_PER_RUN = 5000;
+
+/**
+ * Active and recently-completed runs keyed by app session id.
+ *
+ * This map is the single in-memory source of truth for "is something running
+ * for this session" — the chat websocket handler, abort path, and subscribe
+ * path all consult it instead of asking each provider runtime individually.
+ */
+const runs = new Map<string, ChatRun>();
+
+function evictRunLater(appSessionId: string): void {
+  const timer = setTimeout(() => {
+    const run = runs.get(appSessionId);
+    if (run && run.status === 'completed') {
+      runs.delete(appSessionId);
+    }
+  }, COMPLETED_RUN_RETENTION_MS);
+
+  // Never keep the process alive just to evict a buffered run.
+  timer.unref?.();
+}
+
+/**
+ * Decorates one outbound live event for a run and records it in the event log.
+ *
+ * Responsibilities:
+ * 1. Remap `sessionId` (and `actualSessionId` on `complete`) to the stable
+ *    app session id — provider-native ids never leave the backend.
+ * 2. Assign the next `seq` so clients can detect/replay gaps.
+ * 3. Buffer the event for `chat.subscribe` replay.
+ * 4. Flip the run to `completed` when the terminal `complete` event passes by.
+ */
+function decorateAndRecordEvent(run: ChatRun, message: NormalizedMessage): NormalizedMessage | null {
+  // Exactly-one-complete contract: when a run is aborted the chat handler
+  // emits the terminal `complete` immediately, but the killed runtime may
+  // still emit its own `complete` from its exit handler moments later.
+  // Whichever arrives first wins; the duplicate is dropped here.
+  if (message.kind === 'complete' && run.status === 'completed') {
+    return null;
+  }
+
+  run.lastSeq += 1;
+
+  const outbound: NormalizedMessage = {
+    ...message,
+    sessionId: run.appSessionId,
+    seq: run.lastSeq,
+  };
+
+  if (message.kind === 'complete') {
+    // The provider may report its own id here; the frontend only ever knows
+    // the app id, so the "actual" id is by definition the app id as well.
+    outbound.actualSessionId = run.appSessionId;
+    run.status = 'completed';
+    run.completedAt = Date.now();
+    evictRunLater(run.appSessionId);
+  }
+
+  run.events.push(outbound);
+  if (run.events.length > MAX_BUFFERED_EVENTS_PER_RUN) {
+    run.events.splice(0, run.events.length - MAX_BUFFERED_EVENTS_PER_RUN);
+  }
+
+  return outbound;
+}
+
+/**
+ * Records the provider-native session id for a run and persists the
+ * app-id-to-provider-id mapping so history fetches and future resumes can
+ * address the provider transcript.
+ *
+ * Called from the gateway writer when the runtime either calls
+ * `setSessionId(...)` or emits its `session_created` event — whichever
+ * happens first wins; later calls with the same id are no-ops.
+ */
+function recordProviderSessionId(run: ChatRun, providerSessionId: string): void {
+  if (!providerSessionId || run.providerSessionId === providerSessionId) {
+    return;
+  }
+
+  run.providerSessionId = providerSessionId;
+
+  try {
+    sessionsDb.assignProviderSessionId(run.appSessionId, providerSessionId);
+  } catch (error) {
+    const message = error instanceof Error ? error.message : String(error);
+    console.error('[ChatRunRegistry] Failed to persist provider session id mapping', {
+      appSessionId: run.appSessionId,
+      providerSessionId,
+      error: message,
+    });
+  }
+}
+
+/**
+ * Registry of live provider runs keyed by the stable app session id.
+ *
+ * The registry is what makes the websocket protocol provider-independent:
+ * every run gets a `ChatSessionWriter` that remaps provider-native session
+ * ids to the app id, assigns `seq` numbers, and buffers events for replay —
+ * regardless of which provider runtime produced them.
+ */
+export const chatRunRegistry = {
+  /**
+   * Starts tracking a run and returns it, or `null` when a run is already in
+   * progress for the session (callers must reject the duplicate send).
+   */
+  startRun(input: {
+    appSessionId: string;
+    provider: LLMProvider;
+    providerSessionId: string | null;
+    connection: RealtimeClientConnection;
+    userId: string | number | null;
+  }): ChatRun | null {
+    const existing = runs.get(input.appSessionId);
+    if (existing && existing.status === 'running') {
+      return null;
+    }
+
+    const run: ChatRun = {
+      appSessionId: input.appSessionId,
+      provider: input.provider,
+      providerSessionId: input.providerSessionId,
+      status: 'running',
+      lastSeq: 0,
+      events: [],
+      writer: null as unknown as ChatSessionWriter,
+      startedAt: Date.now(),
+      completedAt: null,
+    };
+
+    run.writer = new ChatSessionWriter({
+      connection: input.connection,
+      userId: input.userId,
+      provider: input.provider,
+      providerSessionId: input.providerSessionId,
+      onProviderSessionId: (providerSessionId) => {
+        recordProviderSessionId(run, providerSessionId);
+      },
+      decorateOutboundEvent: (message) => decorateAndRecordEvent(run, message),
+    });
+
+    runs.set(input.appSessionId, run);
+    return run;
+  },
+
+  getRun(appSessionId: string): ChatRun | undefined {
+    return runs.get(appSessionId);
+  },
+
+  isProcessing(appSessionId: string): boolean {
+    return runs.get(appSessionId)?.status === 'running';
+  },
+
+  /**
+   * Re-attaches a run's outbound stream to a (new) websocket connection.
+   *
+   * This is the generic replacement for the Claude-only writer reconnect:
+   * after a page refresh the new socket subscribes and immediately starts
+   * receiving the still-running stream, for every provider.
+   */
+  attachConnection(appSessionId: string, connection: RealtimeClientConnection): boolean {
+    const run = runs.get(appSessionId);
+    if (!run) {
+      return false;
+    }
+
+    run.writer.updateWebSocket(connection);
+    return true;
+  },
+
+  /**
+   * Returns buffered events with `seq` greater than `afterSeq` for replay.
+   *
+   * An empty array with `run.lastSeq > afterSeq` not covered by the buffer
+   * means the buffer was truncated; the client should refresh over REST.
+   */
+  replayEvents(appSessionId: string, afterSeq: number): NormalizedMessage[] {
+    const run = runs.get(appSessionId);
+    if (!run) {
+      return [];
+    }
+
+    return run.events.filter((event) => typeof event.seq === 'number' && event.seq > afterSeq);
+  },
+
+  /**
+   * Emits a synthetic terminal `complete` if (and only if) the run is still
+   * marked running. Used when a provider runtime throws or resolves without
+   * having produced its own terminal event, and by the abort path.
+   */
+  completeRun(appSessionId: string, opts: { exitCode: number; aborted?: boolean }): void {
+    const run = runs.get(appSessionId);
+    if (!run || run.status !== 'running') {
+      return;
+    }
+
+    run.writer.sendComplete(opts);
+  },
+
+  /**
+   * Test-only escape hatch: clears every tracked run.
+   */
+  clearAll(): void {
+    runs.clear();
+  },
+};