Q15: show which messages each agent actually read

Runs record a context manifest once a model turn succeeds; the chat
marks each human message with the agents that read its current version.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/message-readers.test.ts

@@ -0,0 +1,40 @@
+import { describe, expect, test } from "vitest";
+import { messageReaders } from "../../src/renderer/src/pages/chat/chat-helpers";
+import type { AgentRecord, ChatMessageRecord, TaskRunRecord } from "../../src/shared/domain";
+
+function run(agentId: string | null, contextJson: string | null): TaskRunRecord {
+  return {
+    id: `run_${Math.random()}`, orgId: "org", taskId: "tsk", agentId, providerId: null, providerRequestId: null,
+    executionContextId: null, serviceIdentityId: null, workspaceMountJson: "[]", secretScopeJson: "{}",
+    trigger: "chat_mention", state: "completed", createdAt: "", startedAt: null, completedAt: null, errorMessage: null, contextJson,
+  };
+}
+
+function message(id: string, createdAt: string, editedAt: string | null = null): ChatMessageRecord {
+  return { id, createdAt, editedAt } as ChatMessageRecord;
+}
+
+const agents = [{ id: "a1", name: "CEO" }, { id: "a2", name: "Dana" }] as AgentRecord[];
+const entry = (id: string, version: string) => ({ id, version });
+const manifest = (history: object[], fresh: object[], midRun: object[]) =>
+  JSON.stringify({ threadId: "t", history, fresh, omittedCount: 0, midRun });
+
+describe("message readers", () => {
+  test("collects each agent once per message across history, fresh, and mid-run entries", () => {
+    const messages = [message("m1", "t1"), message("m2", "t2"), message("m3", "t3")];
+    const readers = messageReaders([
+      run("a1", manifest([entry("m1", "t1")], [entry("m2", "t2")], [entry("m3", "t3")])),
+      run("a1", manifest([entry("m2", "t2")], [], [])),
+      run("a2", manifest([], [entry("m2", "t2")], [])),
+      run("a2", null),
+      run(null, manifest([entry("m1", "t1")], [], [])),
+    ], agents, messages);
+    expect(Object.fromEntries(readers)).toEqual({ m1: ["CEO"], m2: ["CEO", "Dana"], m3: ["CEO"] });
+  });
+
+  test("a message edited after it was read is unread until a run sees the new version", () => {
+    const messages = [message("m1", "t1", "t9")];
+    expect(messageReaders([run("a1", manifest([], [entry("m1", "t1")], []))], agents, messages).size).toBe(0);
+    expect(Object.fromEntries(messageReaders([run("a1", manifest([], [entry("m1", "t9")], []))], agents, messages))).toEqual({ m1: ["CEO"] });
+  });
+});