docs(prompt-gate): document unified dispatch invariant

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/prompt-async-route-audit.test.ts

@@ -16,7 +16,7 @@ const RAW_PROMPT_ALLOWLIST = new Map<string, string>([
   ],
   [
     path.join(SOURCE_ROOT, "hooks", "session-recovery", "recover-unavailable-tool.ts"),
-    "runtime type guard checks promptAsync presence before gate-routed promptAsyncAfterSessionIdle",
+    "runtime type guard checks promptAsync presence before gate-routed dispatchInternalPrompt",
   ],
 ])