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/StatusBar.tsx

@@ -9,8 +9,12 @@
  * Workspace page, the open workspace's total (`?lane=` on the same call: the
  * sessions it owns) and the shown session's (`GET /api/pricing/cost/:id` for
  * the URL's `session`, or the focused pane's session from the page's run poll,
- * `LIVE_RUNS_EVENT`), all re-read every 30 s while the tab is visible and
- * whenever the URL names another workspace or session. Each figure carries its
+ * `LIVE_RUNS_EVENT`), all re-read at once whenever the URL names another
+ * workspace or session, then at most every 30 s while events or session
+ * updates arrive (spend only moves with work) and every 2 min otherwise, while
+ * the tab is visible. The session counts re-read only when a session is
+ * created or its status / waiting / archived state changes (every 60 s
+ * otherwise). Each figure carries its
  * token total, and hovering it lists tokens and cost per model. At the right
  * end, the plan quota spent per native tool (`GET /api/pricing/quota`, every
  * 5 min while visible; a click forces a re-read): one "N% used" chip per tool —
@@ -31,9 +35,15 @@ import { fmt, fmtCostFull, formatModelName, timeAgo } from "../lib/format";
 import { AiToolIcon } from "./AiToolIcon";
 import { useLiveRefresh } from "../hooks/useLiveRefresh";
 import { useSpin } from "../hooks/useSpin";
+import { sessionChangeMatcher } from "../lib/sessionChange";
 import { LIVE_RUNS_EVENT, selectedFrom } from "./WorkspaceTree";
 
+/** Spend moves only with work: at most this often while events arrive… */
 const COST_POLL_MS = 30_000;
+/** …and this often regardless (date rollover, budget period, a missed frame). */
+const COST_FALLBACK_MS = 120_000;
+/** The counts' safety poll; session frames that change a count drive the rest. */
+const COUNTS_FALLBACK_MS = 60_000;
 const QUOTA_POLL_MS = 5 * 60_000;
 const QUOTA_TOOL_LABEL: Record<ToolQuota["id"], string> = {
   claude: "Claude",
@@ -384,51 +394,57 @@ export function StatusBar({
       .catch(() => undefined);
   }, []);
   useEffect(loadCounts, [loadCounts]);
-  useLiveRefresh(loadCounts, {
-    intervalMs: 15_000,
-    match: (msg) => msg.type === "session_updated" || msg.type === "session_created",
-  });
+  // Only a frame that moves a session between the counted states (a new
+  // session, a status / waiting / archived change) re-reads: a session row is
+  // re-broadcast on almost every hook.
+  const [countsChanged] = useState(() => sessionChangeMatcher());
+  useLiveRefresh(loadCounts, { intervalMs: COUNTS_FALLBACK_MS, match: countsChanged });
 
+  // Bumped on every lane/session switch: an answer for the previous one is dropped.
+  const costGen = useRef(0);
+  const loadCosts = useCallback(() => {
+    const gen = costGen.current;
+    const live = () => gen === costGen.current;
+    api.pricing
+      .totalCost({ date: localDate() })
+      .then((r) => live() && setToday(r))
+      .catch(() => undefined);
+    api.budgets
+      .status()
+      .then(({ budgets }) => {
+        const hit = budgets.filter((b) => b.crossed.length > 0).sort((a, b) => b.pct - a.pct);
+        if (live()) setBudget(hit[0] ?? null);
+      })
+      .catch(() => undefined);
+    if (lane !== null) {
+      api.pricing
+        .totalCost({ lane })
+        .then((r) => live() && setLaneCost(r))
+        .catch(() => undefined);
+    }
+    if (sessionId) {
+      api.pricing
+        .sessionCost(sessionId)
+        .then((r) => live() && setSessionCost(r))
+        .catch(() => undefined);
+    }
+  }, [lane, sessionId]);
   useEffect(() => {
-    let live = true;
+    costGen.current++;
     // Another workspace or session: never show the previous one's figure.
     setLaneCost(null);
     setSessionCost(null);
-    const tick = () => {
-      if (document.visibilityState !== "visible") return;
-      api.pricing
-        .totalCost({ date: localDate() })
-        .then((r) => live && setToday(r))
-        .catch(() => undefined);
-      api.budgets
-        .status()
-        .then(({ budgets }) => {
-          const hit = budgets.filter((b) => b.crossed.length > 0).sort((a, b) => b.pct - a.pct);
-          if (live) setBudget(hit[0] ?? null);
-        })
-        .catch(() => undefined);
-      if (lane !== null) {
-        api.pricing
-          .totalCost({ lane })
-          .then((r) => live && setLaneCost(r))
-          .catch(() => undefined);
-      }
-      if (sessionId) {
-        api.pricing
-          .sessionCost(sessionId)
-          .then((r) => live && setSessionCost(r))
-          .catch(() => undefined);
-      }
-    };
-    tick();
-    const id = setInterval(tick, COST_POLL_MS);
-    document.addEventListener("visibilitychange", tick);
+    if (document.visibilityState === "visible") loadCosts();
     return () => {
-      live = false;
-      clearInterval(id);
-      document.removeEventListener("visibilitychange", tick);
+      costGen.current++;
     };
-  }, [lane, sessionId]);
+  }, [loadCosts]);
+  useLiveRefresh(loadCosts, {
+    intervalMs: COST_FALLBACK_MS,
+    throttleMs: COST_POLL_MS,
+    match: (msg) =>
+      msg.type === "new_event" || msg.type === "session_updated" || msg.type === "session_created",
+  });
 
   return (
     <footer