fix(session): update cwd on newSession to reflect worktree chdir (#517)

When auto-mode creates a worktree and chdir's into it, the Node process
cwd changes but AgentSession._cwd stays frozen at the original path.
Every newSession() builds a system prompt telling the LLM "Current
working directory: /original/path", so the LLM cd's back there and
writes files to the wrong location.

Update _cwd = process.cwd() at the start of newSession() so the system
prompt reflects the actual working directory after chdir.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/pi-coding-agent/src/core/agent-session.ts

@@ -1354,6 +1354,9 @@ export class AgentSession {
 		this._disconnectFromAgent();
 		await this.abort();
 		this.agent.reset();
+		// Update cwd to current process directory — auto-mode may have chdir'd
+		// into a worktree since the original session was created.
+		this._cwd = process.cwd();
 		this.sessionManager.newSession({ parentSession: options?.parentSession });
 		this.agent.sessionId = this.sessionManager.getSessionId();
 		this._steeringMessages = [];