fix(agent): resolve TypeScript errors with exactOptionalPropertyTypes

- Fix originalToolsConfig assignment to handle undefined properly
- Fix devNull type cast for WritableStream compatibility

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/agent/async-agent.ts

@@ -4,7 +4,7 @@ import { Agent } from "./runner.js";
 import { Channel } from "./channel.js";
 import type { AgentOptions, Message } from "./types.js";
 
-const devNull = { write: () => true } as NodeJS.WritableStream;
+const devNull = { write: () => true } as unknown as NodeJS.WritableStream;
 
 /** Discriminated union of legacy Message (error fallback) and raw AgentEvent */
 export type ChannelItem = Message | AgentEvent;

src/agent/runner.ts

@@ -268,7 +268,9 @@ export class Agent {
     this.agent.setModel(model);
 
     // Save original tools config from options (for later merging during reload)
-    this.originalToolsConfig = options.tools;
+    if (options.tools) {
+      this.originalToolsConfig = options.tools;
+    }
 
     // Merge Profile tools config with options.tools (options takes precedence)
     const profileToolsConfig = this.profile?.getToolsConfig();