Document clientCapabilities persistence in WorkerTransport

Updates documentation to reflect that WorkerTransport now persists
client capabilities across serverless restarts. This fixes an issue
where elicitation and other capability-dependent features would fail
after hibernation or cold starts.

Changes:
- Add initializeParams to TransportState interface documentation
- Document that client capabilities are persisted and restored
- Clarify the behavior of state restoration

Related to cloudflare/agents#783

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: github-actions[bot]

src/content/docs/agents/model-context-protocol/mcp-handler-api.mdx

@@ -390,6 +390,12 @@ interface TransportState {
 	initialized: boolean;
 	initializeParams?: InitializeRequestParams;
 }
+
+interface InitializeRequestParams {
+	capabilities: ClientCapabilities;
+	clientInfo: { name: string; version: string };
+	protocolVersion: string;
+}
 ```
 
 The `TransportState` interface defines what gets persisted to storage: