fix(pier): widen returning identities, warm the Redis store, end stateless listen streams, refuse personal tokens without a TokenID

- Identity.fingerprint covers scopes, both subjects, the ceiling and the
  token kind; a stateful lookup or stateless hit whose fingerprint changed
  re-filters the server with the event diff under its own mutex (A-WR-04)
- Mount warms a Redis store in the background with a 1 s to 30 s backoff
  and every request kicks a pending open without waiting, so stateless-only
  instances subscribe to fan-out (A-WR-05)
- a stateless subscriptions/listen POST re-verifies its bearer every
  recheck interval; an LRU-evicted stateless server closes its sessions
  (A-WR-06)
- resolvePersonalToken refuses a subject with TokenID 0, and the
  pact.MCPPersonalTokenResolver contract says one resolver per application,
  false means unauthorized and TokenID keys the binding (A-WR-09, A-IN-03)

modules/pier/pier.go

@@ -58,10 +58,10 @@ type Pier struct {
 	version    string
 	instance   string
 
-	// stopReap ends the session reaper Mount starts. backpack.App has no
-	// shutdown hook yet, so in production the reaper runs for the life of
-	// the process, like the store subscription; when backpack gains one,
-	// Mount registers stopReap there.
+	// stopReap ends the session reaper (and a Redis store's warm-up) Mount
+	// starts. backpack.App has no shutdown hook yet, so in production the
+	// reaper runs for the life of the process, like the store subscription;
+	// when backpack gains one, Mount registers stopReap there.
 	stopReap context.CancelFunc
 }
 
@@ -72,8 +72,10 @@ type Pier struct {
 // behind the inline throttle. Nothing is mounted when the flag is off. A
 // bad binding, a duplicate name, an unknown guard or a route already
 // registered at mcp.path fails with an error naming the plugin, so boot
-// (and route:list) fail. Nothing dials Redis here. The mounted *Pier is
-// published on the application.
+// (and route:list) fail. Mount never waits for Redis: a Redis store is
+// opened by a background warm-up with a backoff, so the event subscription
+// exists before traffic arrives. Mount also starts the session reaper. The
+// mounted *Pier is published on the application.
 func Mount(host Host, app *backpack.App, plugins []party.Plugin) error {
 	if host == nil || app == nil {
 		return errors.New("pier: a host and an application are required")
@@ -139,13 +141,17 @@ func Mount(host Host, app *backpack.App, plugins []party.Plugin) error {
 	reapCtx, stop := context.WithCancel(context.Background())
 	p.stopReap = stop
 	go p.sessions.reap(reapCtx, reapInterval(cfg.IdleTTL))
+	if ls, ok := p.store.(*lazyStore); ok {
+		go ls.warm(reapCtx)
+	}
 	return nil
 }
 
 // newStore builds the session store mcp.sessions.store selects: the memory
 // store, subscribed to its own events at once, or a Redis store opened on
 // first use from redis.url under cooler's key prefix (nothing dials at
-// mount; a missing URL is a 503 on the first request, logged once).
+// mount itself; a background warm-up opens it with a backoff, and a missing
+// URL is a 503 on stateful requests, logged).
 func (p *Pier) newStore() Store {
 	if p.cfg.SessionStore != StoreRedis {
 		ms := newMemoryStore()