feat(sessions): show a pending-question indicator on session rows

Adds a per-session pending-question badge to sidebar rows, driven by the
live directory-store question state through a dedicated per-session
subscription channel so unrelated streaming never re-renders rows.

Collapsed parent rows roll up pending questions of hidden descendants
from their owning directory stores without bootstrapping them. Question
state is cloned on session delete/archive so badges clear when sessions
disappear. Adds the questionChangeCallbacks sync performance counter,
i18n keys for all locales, and unit tests for the subscription channel
and scope selection.

Fixes #2634

packages/ui/src/sync/sync-context.tsx

@@ -14,6 +14,7 @@ import {
   ChildStoreManager,
   markDirectorySessionPartChanged,
   subscribeDirectoryPermission,
+  subscribeDirectoryQuestions,
   subscribeDirectorySessionMessages,
   type DirectoryBootstrapContext,
   type DirectoryBootstrapReason,
@@ -1620,6 +1621,12 @@ function handleEvent(
     case "session.deleted":
       cloneField("session", (value) => [...value])
       cloneField("permission", (value) => ({ ...value }))
+      if (
+        payload.type === "session.deleted"
+        || (payload.type === "session.updated" && Boolean((payload.properties as { info?: Session }).info?.time.archived))
+      ) {
+        cloneField("question", (value) => ({ ...value }))
+      }
       cloneField("todo", (value) => ({ ...value }))
       cloneField("part", (value) => ({ ...value }))
       cloneField("sessionEventRevision", (value) => ({ ...(value ?? {}) }))
@@ -2436,6 +2443,46 @@ export function useSessionQuestions(sessionID: string, directory?: string) {
   )
 }
 
+/**
+ * Total number of pending questions across the given session scopes. Each
+ * scope names a directory store plus the session IDs to count inside it, so
+ * collapsed subtree rows can roll up pending questions of hidden descendants
+ * from their owning directory stores without bootstrapping them.
+ *
+ * Subscribes through the per-session question sidecar channel, so unrelated
+ * streaming or session activity does not re-render rows.
+ */
+export function useSessionQuestionCount(scopes: readonly { directory: string; sessionIDs: readonly string[] }[]) {
+  const { childStores } = useSyncSystem()
+  const scopedStores = React.useMemo(() => scopes.map((scope) => ({
+    sessionIDs: scope.sessionIDs,
+    store: childStores.ensureChild(scope.directory, { bootstrap: false }),
+  })), [childStores, scopes])
+  React.useEffect(() => {
+    for (const scope of scopes) childStores.pin(scope.directory)
+    return () => {
+      for (const scope of scopes) childStores.unpin(scope.directory)
+    }
+  }, [childStores, scopes])
+  const getSnapshot = React.useCallback(() => {
+    let count = 0
+    for (const { sessionIDs, store } of scopedStores) {
+      const questions = store.getState().question
+      for (const sessionID of sessionIDs) count += questions[sessionID]?.length ?? 0
+    }
+    return count
+  }, [scopedStores])
+  const subscribe = React.useCallback((notify: () => void) => {
+    const unsubscribers = scopedStores.map(({ sessionIDs, store }) => (
+      subscribeDirectoryQuestions(store, sessionIDs, notify)
+    ))
+    return () => {
+      for (const unsubscribe of unsubscribers) unsubscribe()
+    }
+  }, [scopedStores])
+  return React.useSyncExternalStore(subscribe, getSnapshot, getSnapshot)
+}
+
 /** Get sessions list for a directory */
 export function useSessions(directory?: string) {
   return useDirectorySync(