fix(api,runtime): honor session timestamps and add deterministic tie-break in shared-chat-dispatch (#207)

apps/api/src/shared-chat-dispatch.ts

@@ -65,6 +65,11 @@ function eligibleTargets(sessions: PaneCliSession[], panesForRoom: Map<string, P
   return targets;
 }
 
+function compareTimestampsDesc(left: string, right: string): number {
+  const diff = Date.parse(right) - Date.parse(left);
+  return Number.isNaN(diff) ? right.localeCompare(left) : diff;
+}
+
 export async function pickSharedChatDispatchTarget(
   store: SpaceStore,
   runtimeId: string
@@ -86,7 +91,12 @@ export async function pickSharedChatDispatchTarget(
   }
   const targets = eligibleTargets(sessions, panesForRoom);
   if (!targets.length) return null;
-  targets.sort((left, right) => right.session.updatedAt.localeCompare(left.session.updatedAt));
+  targets.sort(
+    (left, right) =>
+      compareTimestampsDesc(left.session.updatedAt, right.session.updatedAt) ||
+      compareTimestampsDesc(left.session.startedAt, right.session.startedAt) ||
+      right.session.sessionId.localeCompare(left.session.sessionId)
+  );
   return targets[0] ?? null;
 }
 

apps/api/tests/shared-chat-dispatch.test.ts

@@ -123,6 +123,69 @@ describe("pickSharedChatDispatchTarget", () => {
     const target = await pickSharedChatDispatchTarget(store, "cli:deepseek");
     expect(target).not.toBeNull();
     expect(target!.pane.id).toBe(newer.pane.id);
+    expect(target!.session.updatedAt).toBe("2026-08-15T10:00:00.000Z");
+  });
+
+  it("breaks ties deterministically by startedAt and sessionId when updatedAt timestamps match", async () => {
+    const store = new InMemorySpaceStore();
+    const paneA = createIdleDeepseekPane(store, "Deepseek A");
+    const paneB = createIdleDeepseekPane(store, "Deepseek B");
+    for (const [pane, sessionId] of [
+      [paneA, "cli_session:alpha"],
+      [paneB, "cli_session:beta"]
+    ] as const) {
+      store.createPaneCliSession({
+        sessionId,
+        paneId: pane.pane.id,
+        roomId: pane.room.id,
+        actorUserId: "user_owner",
+        runtimeId: "cli:deepseek",
+        providerId: "deepseek",
+        modelId: "deepseek-chat",
+        thinkingEffort: "medium",
+        command: "opencode",
+        args: [],
+        cwd: "/workspace",
+        pid: 4200,
+        status: "running",
+        statusReason: null,
+        exitCode: null,
+        isActive: true,
+        startedAt: "2026-08-15T08:00:00.000Z",
+        updatedAt: "2026-08-15T10:00:00.000Z",
+        endedAt: null
+      });
+    }
+
+    const target = await pickSharedChatDispatchTarget(store, "cli:deepseek");
+    expect(target).not.toBeNull();
+    expect(target!.pane.id).toBe(paneB.pane.id);
+  });
+
+  it("compares ISO timestamps by actual instant across timezone offsets", async () => {
+    const store = new InMemorySpaceStore();
+    const olderWithOffset = createIdleDeepseekPane(store, "Deepseek Offset (+02:00)");
+    const newerUtc = createIdleDeepseekPane(store, "Deepseek UTC (Z)");
+    // 11:30+02:00 is 09:30Z, which is 30 minutes earlier than 10:00Z despite sorting later lexicographically
+    createRunningSession(
+      store,
+      olderWithOffset.room.id,
+      olderWithOffset.pane.id,
+      "cli:deepseek",
+      "2026-08-15T11:30:00.000+02:00"
+    );
+    createRunningSession(
+      store,
+      newerUtc.room.id,
+      newerUtc.pane.id,
+      "cli:deepseek",
+      "2026-08-15T10:00:00.000Z"
+    );
+
+    const target = await pickSharedChatDispatchTarget(store, "cli:deepseek");
+    expect(target).not.toBeNull();
+    expect(target!.pane.id).toBe(newerUtc.pane.id);
+    expect(target!.session.updatedAt).toBe("2026-08-15T10:00:00.000Z");
   });
 
   it("only considers the requested runtime", async () => {

packages/contracts/src/schemas.ts

@@ -2401,7 +2401,9 @@ export const createPaneCliSessionInputSchema = paneCliSessionSchema
     codexThreadId: codexThreadIdSchema.nullable().default(null),
     status: paneCliSessionStatusSchema.optional(),
     statusReason: z.string().trim().min(1).max(500).nullable().optional(),
-    isActive: z.boolean().optional()
+    isActive: z.boolean().optional(),
+    startedAt: isoDateTimeSchema.optional(),
+    updatedAt: isoDateTimeSchema.optional()
   });
 
 export const updatePaneCliSessionInputSchema = z

packages/runtime/src/store.ts

@@ -6422,6 +6422,8 @@ export class InMemorySpaceStore implements SpaceStore {
         throw new SpaceConflictError("CLI task revision does not belong to the selected logical task.");
       }
     }
+    const startedAt = parsed.startedAt ?? timestamp;
+    const updatedAt = parsed.updatedAt ?? startedAt;
     const session = paneCliSessionSchema.parse({
       ...parsed,
       sessionId,
@@ -6434,8 +6436,8 @@ export class InMemorySpaceStore implements SpaceStore {
       statusReason: parsed.statusReason ?? null,
       exitCode: null,
       isActive: parsed.isActive ?? true,
-      startedAt: timestamp,
-      updatedAt: timestamp,
+      startedAt,
+      updatedAt,
       endedAt: null
     });
     if (session.isActive) {