perf(client): cut needless polling for local users

- ConversationView: an ended session (SessionDetail, SessionReplay pass
  `ended`) polls its transcript every 60 s instead of 3 s and stops
  rescanning sub-agents; new_event, reconnect and show still fetch at once.
- Workspace: GET /api/run follows run-moving WS messages (lane run
  columns, session created/status change, runs_interrupted) with a 30 s
  fallback, instead of a blind 5 s poll.
- StatusBar: session counts re-read only when a session's
  status/waiting/archived state changes (60 s fallback); costs re-read at
  most every 30 s while work is happening and every 2 min otherwise.
- Dashboard recent activity: 60 s safety poll (was 10 s) plus remote
  import messages; WS still prepends new events.
- New lib/sessionChange.ts matcher with tests.

client/src/components/conversation/ConversationView.tsx

@@ -14,6 +14,10 @@
  * `onOpenTerminal`) and hears how full the context is (`onContext`) and
  * whether its session has started (`onNotStarted`: no row yet — the CLI may
  * be asking in the terminal, e.g. to trust the folder, which this then says).
+ * A caller that knows the session has ended passes `ended`: nothing more is
+ * being written, so the catch-up poll drops from 3 s to 60 s and the
+ * sub-agent list stops being rescanned — a `new_event` frame, a reconnect or
+ * the view being shown again still fetch the tail at once.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 /* =============================================================================
@@ -79,6 +83,9 @@ import type { TranscriptMessage, TranscriptInfo, WSMessage } from "../../lib/typ
 // hook event. A short visibility-gated poll closes that gap and also rescues
 // the conversation from missed/late WebSocket frames.
 const POLL_INTERVAL_MS = 3000;
+// An ended session writes nothing more: a slow safety poll only, in case it was
+// resumed somewhere whose frames this view missed.
+const ENDED_POLL_INTERVAL_MS = 60000;
 // Rescan the transcripts list periodically so new subagents that spawn
 // mid-session appear in the dropdown without a page reload.
 const TRANSCRIPTS_REFRESH_MS = 15000;
@@ -110,6 +117,8 @@ interface ConversationViewProps {
   onContext?: (tokens: number, model: string | null) => void;
   /** A live pane's session has no row yet: the CLI has not started it. */
   onNotStarted?: (notStarted: boolean) => void;
+  /** The session has ended (and no pane holds it): poll slowly, if at all. */
+  ended?: boolean;
 }
 
 function ConversationViewPane({
@@ -124,6 +133,7 @@ function ConversationViewPane({
   stopped = 0,
   onContext,
   onNotStarted,
+  ended = false,
 }: ConversationViewProps) {
   const { t } = useTranslation("sessions");
   const [messages, setMessages] = useState<TranscriptMessage[]>([]);
@@ -188,14 +198,18 @@ function ConversationViewPane({
       }
     }
     loadTranscripts();
-    const interval = window.setInterval(() => {
-      if (isShown(onScreen)) loadTranscripts();
-    }, TRANSCRIPTS_REFRESH_MS);
+    // An ended session spawns no new sub-agents: the load above (re-run when
+    // it ends, for the last ones) is enough.
+    const interval = ended
+      ? undefined
+      : window.setInterval(() => {
+          if (isShown(onScreen)) loadTranscripts();
+        }, TRANSCRIPTS_REFRESH_MS);
     return () => {
       cancelled = true;
       window.clearInterval(interval);
     };
-  }, [sessionId]);
+  }, [sessionId, ended]);
 
   // Sync external initialTranscriptId to internal state
   useEffect(() => {
@@ -355,9 +369,12 @@ function ConversationViewPane({
     let interval: number | null = null;
     function start() {
       if (interval !== null) return;
-      interval = window.setInterval(() => {
-        if (isShown(onScreen)) fetchNewMessages();
-      }, POLL_INTERVAL_MS);
+      interval = window.setInterval(
+        () => {
+          if (isShown(onScreen)) fetchNewMessages();
+        },
+        ended ? ENDED_POLL_INTERVAL_MS : POLL_INTERVAL_MS
+      );
     }
     function stop() {
       if (interval !== null) {
@@ -382,7 +399,7 @@ function ConversationViewPane({
       stop();
       document.removeEventListener("visibilitychange", onVisibility);
     };
-  }, [fetchNewMessages, onScreen]);
+  }, [fetchNewMessages, onScreen, ended]);
 
   // Manual refresh - surfaces a control in the toolbar so users can force
   // a sync without reloading the page.