fix(packages/coding-agent): corrected interactive submit shutdown handling in coding-agent

- Updated submitInteractiveInput to await checkShutdownRequested after submission, avoiding premature teardown (#1020).
- Mapped extension UI shutdown hook to set ctx.shutdownRequested for deferred teardown handling (#1020).
- Added regression coverage for interactive shutdown propagation and issue #1020 teardown behavior.

packages/coding-agent/src/main.ts

@@ -125,7 +125,10 @@ export interface InteractiveModeNotify {
 }
 
 export async function submitInteractiveInput(
-	mode: Pick<InteractiveMode, "markPendingSubmissionStarted" | "finishPendingSubmission" | "showError">,
+	mode: Pick<
+		InteractiveMode,
+		"markPendingSubmissionStarted" | "finishPendingSubmission" | "showError" | "checkShutdownRequested"
+	>,
 	session: Pick<AgentSession, "prompt">,
 	input: SubmittedUserInput,
 ): Promise<void> {
@@ -144,6 +147,7 @@ export async function submitInteractiveInput(
 		mode.showError(errorMessage);
 	} finally {
 		mode.finishPendingSubmission(input);
+		await mode.checkShutdownRequested();
 	}
 }
 

packages/coding-agent/src/modes/controllers/extension-ui-controller.ts

@@ -119,7 +119,10 @@ export class ExtensionUiController {
 			abort: () => this.ctx.session.abort(),
 			hasPendingMessages: () => this.ctx.session.queuedMessageCount > 0,
 			shutdown: () => {
-				// Signal shutdown request (will be handled by main loop)
+				// Defer the actual teardown to the main loop, which calls
+				// `checkShutdownRequested()` at idle boundaries so any queued
+				// steering / follow-up messages drain first (see issue #1020).
+				this.ctx.shutdownRequested = true;
 			},
 			getContextUsage: () => this.ctx.session.getContextUsage(),
 			compact: instructionsOrOptions => this.#compactSession(instructionsOrOptions),