fix: harden bounded state sidecars

N-05: the conditional-validator key was a colon join over components that may
themselves contain colons, so two distinct valid bindings could collide and one
definition's ETag could be prepared for another. The key is now a validated,
byte-bounded fixed tuple encoded with JSON.stringify.

N-09: capture localStorage exactly once and compare StorageEvent.storageArea
against that object identity, so a pulse from sessionStorage or any other area
is rejected instead of matching on key and value alone. The pulse key is
registered in the storage registry as CACHE_INVALIDATION_PULSE.

N-10: race loadPage against the caller signal and re-check before observing a
page, so a non-cooperative loader can neither hold loadAll forever nor have a
post-abort completion accumulated into a successful result.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/contracts/storage-keys.ts

@@ -69,6 +69,18 @@ export const STORAGE_REGISTRY = Object.freeze({
     migration: "discard",
     quotaFallback: "feature-disable",
   }),
+  CACHE_INVALIDATION_PULSE: defineStorageKey({
+    logicalName: "CACHE_INVALIDATION_PULSE",
+    scope: "cache-invalidation",
+    name: "pulse",
+    backend: "localStorage",
+    classification: "opaque-cache",
+    schemaVersion: 1,
+    valueCodec: "opaque-string-v1",
+    ttl: null,
+    migration: "discard",
+    quotaFallback: "no-persist",
+  }),
   AUTH_TOKEN: defineStorageKey({
     logicalName: "AUTH_TOKEN",
     scope: "auth",