fix: prefer fresh codex activity in conversation timestamps

tests/conversation-home-items.test.ts

@@ -8,6 +8,7 @@ let runtimeRoot = "";
 let readState: (typeof import("../src/lib/boss-data"))["readState"];
 let getConversationHomeItems: (typeof import("../src/lib/boss-projections"))["getConversationHomeItems"];
 let getConversationFolderView: (typeof import("../src/lib/boss-projections"))["getConversationFolderView"];
+let formatTimestampLabel: (typeof import("../src/lib/boss-projections"))["formatTimestampLabel"];
 
 async function setup() {
   if (runtimeRoot) return;
@@ -22,6 +23,7 @@ async function setup() {
   readState = data.readState;
   getConversationHomeItems = projections.getConversationHomeItems;
   getConversationFolderView = projections.getConversationFolderView;
+  formatTimestampLabel = projections.formatTimestampLabel;
 }
 
 test.after(async () => {
@@ -199,3 +201,35 @@ test("conversation items keep a safe context ring even when no thread snapshot e
   assert.equal(directThread?.contextBudgetIndicator.percent, 100);
   assert.equal(directThread?.contextBudgetIndicator.level, "safe");
 });
+
+test("conversation items prefer latest observed codex activity over stale last message time", async () => {
+  await setup();
+  const state = await readState();
+  const baseProject = buildImportedThreadProject(
+    "mac-studio",
+    "stale-thread",
+    "Talking",
+    "talking",
+    "树莓派二代查询",
+    "thread-stale",
+    "2026-04-04T06:12:00+08:00",
+  );
+
+  state.projects = state.projects.filter((project) => project.id === "master-agent");
+  state.projects.push(
+    {
+      ...baseProject,
+      threadMeta: {
+        ...baseProject.threadMeta,
+        lastObservedCodexActivityAt: "2026-04-04T11:48:00+08:00",
+      },
+    },
+  );
+
+  const items = getConversationHomeItems(state);
+  const thread = items.find((item) => item.projectId === "stale-thread");
+
+  assert.ok(thread);
+  assert.equal(thread?.latestReplyAt, "2026-04-04T11:48:00+08:00");
+  assert.equal(thread?.latestReplyLabel, formatTimestampLabel("2026-04-04T11:48:00+08:00"));
+});