fix(multiuser): close cross-user web-layer scoping holes found in review

The opt-in multi-user feature's only enforcement is web-layer scoping
(all sessions share one OS account). An adversarial review found 8 critical
+ 7 high cross-user holes that defeated it, plus mediums; all fixed here.
Single-user (flag-off) behavior stays byte-identical apart from documented
consistency deltas.

Ownership / confinement:
- DELETE /api/sessions (bulk) + /:id now owner-scope / findSessionOrFail
- quick-start, cron (create+fire), scheduled runs confine workingDir to the
  owner's space; case link/docker-link/docker-import confine the host path
- resolveCasePath no longer resolves linked cases for non-admins; foreign
  remote/docker cases are skipped (fall through to the caller's own local case)
- history, subagents/workflows, mux-sessions, orchestrator, cron run-history,
  away-digest, and remote/docker host reads are owner- or admin-scoped

Permission policy (section 6.3):
- non-granted users are downgraded at every spawn site incl. legacy
  /api/scheduled, PlanOrchestrator one-shots, remote launch, and the cron-fire
  gemini/codex bypass switches; resolveClaudeModeForUsername now fails closed

Auth / store:
- verify-first login throttle (a correct password is never locked out),
  /ws terminal subject to the change-password lockbox, cookie fast-path
  re-validates identity live, role/grant changes revoke sessions, admin delete
  runs the last-admin guard before any teardown
- users.json: distinguish missing (ENOENT) from corrupt/unreadable so a bad
  read can't overwrite all accounts; unique per-process temp write path

Event streams:
- debounced session:updated + batched task:updated, clipboard, and push
  notifications route by owner (fail closed); getLightState hides machine-wide
  globalStats from non-admins

Tests: two suites updated to assert the fixed (secure) behavior. tsc, eslint,
and test:ci all green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/push-store.ts

@@ -9,10 +9,23 @@
 import { existsSync, readFileSync, writeFileSync, mkdirSync } from 'node:fs';
 import { join } from 'node:path';
 import webpush from 'web-push';
-import type { VapidKeys, PushSubscriptionRecord } from './types.js';
+import type { VapidKeys, PushSubscriptionRecord, UserRole } from './types.js';
 import { Debouncer } from './utils/index.js';
 import { getDataDir } from './config/instance.js';
 
+/**
+ * A push subscription plus the multi-user owner identity stamped at subscribe time.
+ * `username`/`role` are undefined in single-user mode (and for legacy records saved
+ * before this field existed). sendPushNotifications uses them to scope a
+ * session-notification to its owner's devices (+ admins) instead of fanning out to
+ * every user. Kept as a store-local widening of PushSubscriptionRecord so the shared
+ * type stays untouched; the extra keys serialize/persist transparently.
+ */
+export type OwnedPushSubscriptionRecord = PushSubscriptionRecord & {
+  username?: string;
+  role?: UserRole;
+};
+
 const DATA_DIR = getDataDir();
 const KEYS_FILE = join(DATA_DIR, 'push-keys.json');
 const SUBS_FILE = join(DATA_DIR, 'push-subscriptions.json');
@@ -20,7 +33,7 @@ const SAVE_DEBOUNCE_MS = 500;
 
 export class PushSubscriptionStore {
   private vapidKeys: VapidKeys | null = null;
-  private subscriptions: Map<string, PushSubscriptionRecord> = new Map();
+  private subscriptions: Map<string, OwnedPushSubscriptionRecord> = new Map();
   private saveDeb = new Debouncer(SAVE_DEBOUNCE_MS);
   private _disposed = false;
 
@@ -67,17 +80,19 @@ export class PushSubscriptionStore {
   }
 
   /** Register or update a push subscription (deduplicates by endpoint) */
-  addSubscription(sub: Omit<PushSubscriptionRecord, 'lastUsedAt'>): PushSubscriptionRecord {
+  addSubscription(sub: Omit<OwnedPushSubscriptionRecord, 'lastUsedAt'>): OwnedPushSubscriptionRecord {
     // Check for existing subscription with same endpoint
     for (const [existingId, existing] of this.subscriptions) {
       if (existing.endpoint === sub.endpoint) {
-        // Update existing
-        const updated: PushSubscriptionRecord = {
+        // Update existing (re-stamp owner identity so it tracks the current caller)
+        const updated: OwnedPushSubscriptionRecord = {
           ...existing,
           keys: sub.keys,
           userAgent: sub.userAgent,
           lastUsedAt: Date.now(),
           pushPreferences: sub.pushPreferences,
+          username: sub.username,
+          role: sub.role,
         };
         this.subscriptions.set(existingId, updated);
         this.scheduleSave();
@@ -86,7 +101,7 @@ export class PushSubscriptionStore {
     }
 
     // New subscription
-    const record: PushSubscriptionRecord = {
+    const record: OwnedPushSubscriptionRecord = {
       ...sub,
       lastUsedAt: Date.now(),
     };
@@ -96,7 +111,7 @@ export class PushSubscriptionStore {
   }
 
   /** Update push preferences for a subscription */
-  updatePreferences(id: string, preferences: Record<string, boolean>): PushSubscriptionRecord | null {
+  updatePreferences(id: string, preferences: Record<string, boolean>): OwnedPushSubscriptionRecord | null {
     const sub = this.subscriptions.get(id);
     if (!sub) return null;
     sub.pushPreferences = preferences;
@@ -124,12 +139,12 @@ export class PushSubscriptionStore {
   }
 
   /** Get all subscriptions */
-  getAll(): PushSubscriptionRecord[] {
+  getAll(): OwnedPushSubscriptionRecord[] {
     return Array.from(this.subscriptions.values());
   }
 
   /** Get a single subscription by ID */
-  get(id: string): PushSubscriptionRecord | null {
+  get(id: string): OwnedPushSubscriptionRecord | null {
     return this.subscriptions.get(id) ?? null;
   }
 
@@ -138,7 +153,7 @@ export class PushSubscriptionStore {
     if (!existsSync(SUBS_FILE)) return;
     try {
       const raw = readFileSync(SUBS_FILE, 'utf-8');
-      const arr = JSON.parse(raw) as PushSubscriptionRecord[];
+      const arr = JSON.parse(raw) as OwnedPushSubscriptionRecord[];
       for (const sub of arr) {
         this.subscriptions.set(sub.id, sub);
       }