feat(mobile): synchronized pill composer transitions and draft screen fixes

Drop the animated pill/composer morph in favor of instant swaps that are
synchronized with the keyboard choreography: a new oc:keyboard-intent
event collapses the composer (flushSync) before the hide compensation is
measured, so keyboard travel and composer height change land as a single
chat motion on both iOS and Android (Android also gains keyboard signals
and deterministic re-pins around its native resize). The WKWebView caret
is hidden during the transition so it no longer flies to its new position.

Draft screen: starter chips hide instantly while the keyboard is up and
the centered title rides the keyboard shift compensation instead of
double-jumping; the composer drag handle also works in dictation mode;
the highlight mirror is disabled on mobile so the caret matches the text.

Fixes: worktree discovery and the GitHub auth probe now wait for the
runtime connection (no more empty branch pickers / stale auth on cold
start), worktree discovery merges per project instead of clobbering the
persisted map, the cross-project session list resets on instance switch
(with an in-flight load guard) so no stale sessions linger, and mobile
overlay content contains its overscroll instead of bouncing the page.

packages/ui/src/stores/useGlobalSessionsStore.ts

@@ -25,11 +25,17 @@ type GlobalSessionsState = {
   upsertSession: (session: Session) => void;
   removeSessions: (ids: Iterable<string>) => void;
   archiveSessions: (ids: Iterable<string>, archivedAt?: number) => void;
+  /** Drop every session from the previous runtime instance and go back to the
+      unloaded state, so a fresh load runs against the new endpoint. */
+  resetForRuntimeSwitch: () => void;
 };
 
 const PAGE_SIZE = 500;
 
 let inflightLoad: Promise<LoadResult> | null = null;
+// Bumped on runtime switch: an in-flight load from the previous instance must
+// not apply its (stale) snapshot after the reset.
+let loadGeneration = 0;
 
 const normalizePath = (value?: string | null): string | null => {
   if (typeof value !== 'string') {
@@ -363,6 +369,19 @@ export const useGlobalSessionsStore = create<GlobalSessionsState>((set, get) =>
     set((state) => applySnapshot(state, activeSessions, archivedSessions, status));
   },
 
+  resetForRuntimeSwitch: () => {
+    loadGeneration += 1;
+    inflightLoad = null;
+    set({
+      activeSessions: [],
+      archivedSessions: [],
+      sessionsByDirectory: new Map(),
+      reviewTransferBySessionId: new Map(),
+      hasLoaded: false,
+      status: 'idle',
+    });
+  },
+
   loadSessions: async (fallbackActive) => {
     if (inflightLoad) {
       return inflightLoad;
@@ -370,6 +389,7 @@ export const useGlobalSessionsStore = create<GlobalSessionsState>((set, get) =>
 
     set((state) => (state.status === 'loading' ? state : { status: 'loading' }));
 
+    const generation = loadGeneration;
     inflightLoad = (async () => {
       const current = get();
 
@@ -395,9 +415,17 @@ export const useGlobalSessionsStore = create<GlobalSessionsState>((set, get) =>
           console.warn('[GlobalSessions] Failed to load archived sessions, preserving current snapshot:', archivedResult.reason);
         }
 
+        if (generation !== loadGeneration) {
+          // Runtime switched mid-load: this snapshot belongs to the previous
+          // instance — drop it.
+          return { activeSessions: [], archivedSessions: [] };
+        }
         set((state) => applySnapshot(state, nextActiveSessions, nextArchivedSessions, 'ready'));
         return { activeSessions: nextActiveSessions, archivedSessions: nextArchivedSessions };
       } catch (error) {
+        if (generation !== loadGeneration) {
+          return { activeSessions: [], archivedSessions: [] };
+        }
         const nextActiveSessions = mergeSessionLists(current.activeSessions, fallbackActive);
         const nextArchivedSessions = current.archivedSessions;
         console.warn('[GlobalSessions] Failed to load sessions, using fallback snapshot:', error);