feat(coding-agent): add set_session_name RPC command (#1075)

- Add set_session_name command with empty name validation
- Expose sessionName in get_state response
- Add setSessionName() to AgentSession and RpcClient
- Document in docs/rpc.md

packages/coding-agent/src/modes/rpc/rpc-client.ts

@@ -362,6 +362,13 @@ export class RpcClient {
 		return this.getData<{ text: string | null }>(response).text;
 	}
 
+	/**
+	 * Set the session display name.
+	 */
+	async setSessionName(name: string): Promise<void> {
+		await this.send({ type: "set_session_name", name });
+	}
+
 	/**
 	 * Get all messages in the session.
 	 */