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/events.go

@@ -79,6 +79,7 @@ func (p *Pier) recomputeSession(ctx context.Context, ls *localSession, relink bo
 	}
 	tools, prompts := p.catalog.allowed(ctx, id)
 	applyDiff(ls.server, p, id, tools, prompts, ls.tools, ls.prompts)
+	ls.fingerprint = id.fingerprint()
 	ls.mu.Unlock()
 }
 
@@ -92,9 +93,28 @@ func (p *Pier) recomputeStateless(ctx context.Context, e *statelessEntry, relink
 	}
 	tools, prompts := p.catalog.allowed(ctx, id)
 	applyDiff(e.server, p, id, tools, prompts, e.tools, e.prompts)
+	e.fingerprint = id.fingerprint()
 	e.mu.Unlock()
 }
 
+// widen re-filters a cached server for the identity of the request that
+// reached it when that identity's fingerprint differs from the one the
+// server was last filtered for (A-WR-04): a binding that returns with more
+// scope, or with a backend subject added, gains the newly allowed tools and
+// prompts at once, and one that returns with less loses them. The caller
+// holds the session's or entry's own mutex, never a router-wide one.
+func (p *Pier) widen(ctx context.Context, srv serverFeatures, id Identity, fp *string, haveTools, havePrompts map[string]bool) {
+	next := id.fingerprint()
+	if *fp == next {
+		return
+	}
+	// A client that hangs up mid-check must not leave the server filtered
+	// by cancelled guard checks (an error hides the item).
+	tools, prompts := p.catalog.allowed(context.WithoutCancel(ctx), id)
+	applyDiff(srv, p, id, tools, prompts, haveTools, havePrompts)
+	*fp = next
+}
+
 // applyDiff brings a server's tool and prompt sets to the allowed ones,
 // updating the tracking maps in place.
 func applyDiff(srv serverFeatures, p *Pier, id Identity, tools []*tool, prompts []*prompt, haveTools, havePrompts map[string]bool) {