fix(coding-agent): guarded fork during streaming

- Blocked /fork while streaming to avoid split session logs.

- Preserved queued and next-turn messages when forking.

packages/coding-agent/src/modes/controllers/command-controller.ts

@@ -419,6 +419,10 @@ export class CommandController {
 	}
 
 	async handleForkCommand(): Promise<void> {
+		if (this.ctx.session.isStreaming) {
+			this.ctx.showWarning("Wait for the current response to finish or abort it before forking.");
+			return;
+		}
 		if (this.ctx.loadingAnimation) {
 			this.ctx.loadingAnimation.stop();
 			this.ctx.loadingAnimation = undefined;

packages/coding-agent/src/modes/interactive-mode.ts

@@ -212,11 +212,13 @@ export class InteractiveMode implements InteractiveModeContext {
 			{ name: "login", description: "Login with OAuth provider" },
 			{ name: "logout", description: "Logout from OAuth provider" },
 			{ name: "new", description: "Start a new session" },
+			{ name: "fork", description: "Duplicate current session into a new session" },
 			{ name: "compact", description: "Manually compact the session context" },
 			{ name: "handoff", description: "Hand off the session context to a new session" },
 			{ name: "background", description: "Detach UI and continue running in background" },
 			{ name: "bg", description: "Alias for /background" },
 			{ name: "resume", description: "Resume a different session" },
+			{ name: "debug", description: "Write debug log (TUI state and messages)" },
 			{ name: "exit", description: "Exit the application" },
 		];
 

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

@@ -1710,11 +1710,6 @@ export class AgentSession {
 		// Update agent session ID
 		this.agent.sessionId = this.sessionManager.getSessionId();
 
-		// Clear queued messages (they would be duplicated otherwise)
-		this._steeringMessages = [];
-		this._followUpMessages = [];
-		this._pendingNextTurnMessages = [];
-
 		// Emit session_switch event with reason "fork" to hooks
 		if (this._extensionRunner) {
 			await this._extensionRunner.emit({