fix(activity): keep badge in step with monitoring turns; drop dead cache branch (#19535)

Monitoring turns emit no working event (4b2e3dded0), so the titlebar
badge must not count them either, or it lights with no unread row to
clear. The build cache's cached-events ternary could never take its
cached path because the early return above already covers it.

src/renderer/src/components/activity/activity-event-build-cache.ts

@@ -87,21 +87,19 @@ export function resolvePaneBuild(
     return { events: cached.events, live: cached.live }
   }
 
-  const events =
-    inputsUnchanged && liveMatchesCache
-      ? cached.events
-      : buildPaneActivityEvents({
-          entry: rowEntry,
-          worktree: request.worktree,
-          repo: request.repo,
-          tab: request.tab,
-          agentType: request.agentType,
-          agentAlive: request.agentAlive,
-          acknowledgedAt: request.acknowledgedAt,
-          clearedAt: request.clearedAt,
-          liveState: request.liveState,
-          migrationUnsupportedPtyId: request.migrationUnsupportedPtyId
-        })
+  // The live turn is itself an event, so a live change always rebuilds the pane's events.
+  const events = buildPaneActivityEvents({
+    entry: rowEntry,
+    worktree: request.worktree,
+    repo: request.repo,
+    tab: request.tab,
+    agentType: request.agentType,
+    agentAlive: request.agentAlive,
+    acknowledgedAt: request.acknowledgedAt,
+    clearedAt: request.clearedAt,
+    liveState: request.liveState,
+    migrationUnsupportedPtyId: request.migrationUnsupportedPtyId
+  })
   const live: ActivityLiveAgentSnapshot | null =
     request.liveState === null
       ? null

src/renderer/src/components/activity/useActivityUnreadCount.test.ts

@@ -114,13 +114,14 @@ describe('countActivityUnread source overlap', () => {
 })
 
 describe('countActivityUnread working turns', () => {
-  it('counts fresh working and monitoring, but not historical or retained working', () => {
+  it('counts fresh working, but not monitoring, historical, or retained working', () => {
     const entry = makeEntry({
       state: 'working',
       stateHistory: [{ state: 'working', prompt: 'old', startedAt: 1_000 }]
     })
     expect(countActivityUnread(makeSource(entry), 2_000)).toBe(1)
-    expect(countActivityUnread(makeSource({ ...entry, workingMode: 'monitoring' }), 2_000)).toBe(1)
+    // Monitoring emits no unread event in the list (4b2e3dded0), so the badge must not count it.
+    expect(countActivityUnread(makeSource({ ...entry, workingMode: 'monitoring' }), 2_000)).toBe(0)
     expect(
       countActivityUnread(
         {

src/renderer/src/components/activity/useActivityUnreadCount.ts

@@ -39,9 +39,11 @@ export function countActivityUnread(source: ActivityUnreadCountSource, now = Dat
       }
     }
     // Why: a session-boundary done is an idle connect (STA-3386), not an event to read.
+    // Why 'working' only: a monitoring turn surfaces through the live snapshot, never as an
+    // unread event, so counting it here would light the badge with no unread row to clear.
     if (
       (isHistoricalActivityState(entry.state) ||
-        (live && freshActivityLiveAgentState(entry, now) !== null)) &&
+        (live && freshActivityLiveAgentState(entry, now) === 'working')) &&
       entry.sessionBoundary !== true &&
       mutedAt < entry.stateStartedAt
     ) {