CL-6795: keep sidebar preview across join/event rows (server)

packages/chat/src/index.ts

@@ -304,6 +304,7 @@ export {
   createDrizzleRoomMessageStore,
   createInMemoryRoomMessageStore,
   postRoomMessage,
+  previewOf,
 } from "./room-messages";
 export type {
   RoomMessage,

packages/chat/src/room-messages.test.ts

@@ -296,6 +296,84 @@ describe("listActivity", () => {
     expect(activity[WORKBENCH]?.preview).not.toMatch(/model key/i);
     expect(activity[WORKBENCH]?.preview).not.toMatch(/ref /i);
   });
+
+  // CL-6795: bench-list preview settles on the latest person-facing text —
+  // never a blank title-only row while readable messages exist, and never a
+  // stale greeting preferred over a newer human message.
+  test("a newer user message previews over a stale agent greeting", async () => {
+    const roomMessages = createInMemoryRoomMessageStore();
+    const publisher = recordingPublisher();
+    await postRoomMessage(
+      { roomMessages, publish: publisher.publish },
+      {
+        tenantId: TENANT,
+        workbenchId: WORKBENCH,
+        sender: { name: "Myra", address: "run_myra@acme.example" },
+        runId: "run_myra",
+        parts: [
+          { kind: "text", text: "Hi — I'm Myra. What are we working on?" },
+        ],
+      },
+    );
+    await Bun.sleep(2);
+    const user = await postRoomMessage(
+      { roomMessages, publish: publisher.publish },
+      {
+        tenantId: TENANT,
+        workbenchId: WORKBENCH,
+        sender: { name: null, address: "prn_ada@acme.example" },
+        parts: [{ kind: "text", text: "draft the agenda for Monday" }],
+      },
+    );
+
+    const activity = await roomMessages.listActivity({
+      tenantId: TENANT,
+      workbenches: [{ workbenchId: WORKBENCH }],
+    });
+
+    expect(activity[WORKBENCH]?.lastActivityAt).toBe(user.createdAt);
+    expect(activity[WORKBENCH]?.preview).toBe("draft the agenda for Monday");
+    expect(activity[WORKBENCH]?.preview).not.toMatch(/I'm Myra/i);
+  });
+
+  test("a join notice after readable text keeps the prior preview, never blanks", async () => {
+    const roomMessages = createInMemoryRoomMessageStore();
+    const publisher = recordingPublisher();
+    await postRoomMessage(
+      { roomMessages, publish: publisher.publish },
+      {
+        tenantId: TENANT,
+        workbenchId: WORKBENCH,
+        sender: { name: null, address: "prn_ada@acme.example" },
+        parts: [{ kind: "text", text: "let's pull Scout in" }],
+      },
+    );
+    await Bun.sleep(2);
+    const joined = await postRoomMessage(
+      { roomMessages, publish: publisher.publish },
+      {
+        tenantId: TENANT,
+        workbenchId: WORKBENCH,
+        sender: { name: null, address: "run_scout@acme.example" },
+        runId: "run_scout",
+        parts: [
+          {
+            kind: "event",
+            event: "workbench.agent-joined",
+            data: { address: "run_scout@acme.example" },
+          },
+        ],
+      },
+    );
+
+    const activity = await roomMessages.listActivity({
+      tenantId: TENANT,
+      workbenches: [{ workbenchId: WORKBENCH }],
+    });
+
+    expect(activity[WORKBENCH]?.lastActivityAt).toBe(joined.createdAt);
+    expect(activity[WORKBENCH]?.preview).toBe("let's pull Scout in");
+  });
 });
 
 describe("previewOf", () => {

packages/chat/src/room-messages.ts

@@ -181,8 +181,9 @@ function isFailurePreviewParts(parts: readonly Part[]): boolean {
  * Pick bench-list preview text from newest-first messages: skip failed
  * turns and classified failure paragraphs, keep the last good human/agent
  * text, and fall back to the short consumer notice when nothing else
- * qualifies (CL-6735). Does not skip ordinary user/agent replies
- * (CL-6795 is separate).
+ * qualifies (CL-6735). Event / attachment-only rows contribute no text and
+ * are walked past so a join notice never blanks a prior readable preview
+ * (CL-6795). Ordinary user/agent replies are never skipped.
  */
 function activityPreviewFromNewestFirst(
   newestFirst: readonly RoomMessage[],
@@ -199,6 +200,12 @@ function activityPreviewFromNewestFirst(
   return "";
 }
 
+/** True when listActivity must walk back past the newest row for a preview
+ * (CL-6735 failures; CL-6795 empty event/attachment-only newest). */
+function needsPreviewLookback(parts: readonly Part[]): boolean {
+  return isFailurePreviewParts(parts) || previewOf(parts).length === 0;
+}
+
 function summaryOf(
   newest: RoomMessage,
   unreadCount: number,
@@ -430,7 +437,7 @@ export function createDrizzleRoomMessageStore(
         const newest = toRoomMessage(row as MessageRow);
         const unreadCount = unreadByWorkbenchId.get(newest.workbenchId) ?? 0;
         let newestFirstForPreview: readonly RoomMessage[] = [newest];
-        if (isFailurePreviewParts(newest.parts)) {
+        if (needsPreviewLookback(newest.parts)) {
           const recentRows = await db
             .select()
             .from(workbenchMessages)

packages/chat/test/room-activity.drizzle.test.ts

@@ -188,4 +188,44 @@ describeIfDb("createDrizzleRoomMessageStore: listActivity", () => {
       await sql.end();
     }
   });
+
+  // CL-6795: a join/event newest row must not blank the list preview while
+  // earlier readable text still exists.
+  test("a join notice after readable text keeps the prior preview", async () => {
+    const sql = postgres(scratchUrl, { max: 5, onnotice: () => undefined });
+    try {
+      const store = createDrizzleRoomMessageStore(drizzle(sql));
+      await store.insertMessage({
+        id: "msg_join_keep_1",
+        tenantId: TENANT,
+        workbenchId: "run_join_keep",
+        sender: { name: null, address: "prn_alice@acme.example" },
+        parts: [{ kind: "text", text: "let's pull Scout in" }],
+      });
+      const joined = await store.insertMessage({
+        id: "msg_join_keep_2",
+        tenantId: TENANT,
+        workbenchId: "run_join_keep",
+        sender: { name: null, address: "run_scout@acme.example" },
+        runId: "run_scout",
+        parts: [
+          {
+            kind: "event",
+            event: "workbench.agent-joined",
+            data: { address: "run_scout@acme.example" },
+          },
+        ],
+      });
+
+      const activity = await store.listActivity({
+        tenantId: TENANT,
+        workbenches: [{ workbenchId: "run_join_keep" }],
+      });
+
+      expect(activity["run_join_keep"]?.lastActivityAt).toBe(joined.createdAt);
+      expect(activity["run_join_keep"]?.preview).toBe("let's pull Scout in");
+    } finally {
+      await sql.end();
+    }
+  });
 });