Guard remote fork source state

roblourens · roblourens · commit d4f79a2fb7ce · 2026-04-12T12:52:29.000-07:00
Written by Copilot
diff --git a/src/vs/platform/agentHost/electron-browser/remoteAgentHostProtocolClient.ts b/src/vs/platform/agentHost/electron-browser/remoteAgentHostProtocolClient.ts
@@ -199,7 +199,10 @@ export class RemoteAgentHostProtocolClient extends Disposable implements IAgentC
 			return undefined;
 		}
 		const sourceState = this.getSubscriptionUnmanaged<ISessionState>(StateComponents.Session, fork.session)?.value;
-		const turnId = sourceState?.turns[fork.turnIndex]?.id;
+		if (!sourceState || sourceState instanceof Error) {
+			throw new Error(`Cannot fork: protocol state for ${fork.session.toString()} is not available`);
+		}
+		const turnId = sourceState.turns[fork.turnIndex]?.id;
 		if (!turnId) {
 			throw new Error(`Cannot fork: turn index ${fork.turnIndex} not found in protocol state for ${fork.session.toString()}`);
 		}

Original file line number	Diff line number	Diff line change
`@@ -199,7 +199,10 @@ export class RemoteAgentHostProtocolClient extends Disposable implements IAgentC`
`199`	`199`	`return undefined;`
`200`	`200`	`}`
`201`	`201`	`const sourceState = this.getSubscriptionUnmanaged<ISessionState>(StateComponents.Session, fork.session)?.value;`
`202`		`- const turnId = sourceState?.turns[fork.turnIndex]?.id;`
	`202`	`+ if (!sourceState \|\| sourceState instanceof Error) {`
	`203`	+ throw new Error(`Cannot fork: protocol state for ${fork.session.toString()} is not available`);
	`204`	`+ }`
	`205`	`+ const turnId = sourceState.turns[fork.turnIndex]?.id;`
`203`	`206`	`if (!turnId) {`
`204`	`207`	throw new Error(`Cannot fork: turn index ${fork.turnIndex} not found in protocol state for ${fork.session.toString()}`);
`205`	`208`	`}`