🤖 fix: treat default Continue as resume sentinel (#1137)

### What changed
- Use a short resume sentinel ("Continue") for forced compaction.
- Don't inject that sentinel into the compaction *prompt* (summary
request), while still keeping it in compaction metadata so the backend
can auto-send it after compaction.
- Add unit coverage for the default vs. explicit follow-up behavior.

### Why
Appending a verbose auto-injected instruction can compete with the
user's actual message; treating "Continue" as a control sentinel and
keeping it out of the summarization prompt reduces instruction
confusion.

---
_Generated with `mux` • Model: `unknown` • Thinking: `unknown`_

Author: ammar-agent

src/browser/components/AIView.tsx

@@ -190,14 +190,17 @@ const AIViewInner: React.FC<AIViewProps> = ({
   // Show warning when: shouldShowWarning flag is true AND not currently compacting
   const shouldShowCompactionWarning = !isCompacting && autoCompactionResult.shouldShowWarning;
 
-  // Handle force compaction callback - memoized to avoid effect re-runs
+  // Handle force compaction callback - memoized to avoid effect re-runs.
+  // We pass a default continueMessage of "Continue" as a resume sentinel so the backend can
+  // auto-send it after compaction. The compaction prompt builder special-cases this sentinel
+  // to avoid injecting it into the summarization request.
   const handleForceCompaction = useCallback(() => {
     if (!api) return;
     void executeCompaction({
       api,
       workspaceId,
       sendMessageOptions: pendingSendOptions,
-      continueMessage: { text: "Continue with the current task" },
+      continueMessage: { text: "Continue" },
     });
   }, [api, workspaceId, pendingSendOptions]);
 

src/browser/utils/chatCommands.test.ts

@@ -166,6 +166,35 @@ describe("prepareCompactionMessage", () => {
     expect(metadata.parsed.continueMessage?.text).toBe("Continue with this");
   });
 
+  test("omits default resume text from compaction prompt", () => {
+    const sendMessageOptions = createBaseOptions();
+    const { messageText, metadata } = prepareCompactionMessage({
+      workspaceId: "ws-1",
+      continueMessage: { text: "Continue" },
+      sendMessageOptions,
+    });
+
+    expect(messageText).not.toContain("The user wants to continue with: Continue");
+
+    if (metadata.type !== "compaction-request") {
+      throw new Error("Expected compaction metadata");
+    }
+
+    // Still queued for auto-send after compaction
+    expect(metadata.parsed.continueMessage?.text).toBe("Continue");
+  });
+
+  test("includes non-default continue text in compaction prompt", () => {
+    const sendMessageOptions = createBaseOptions();
+    const { messageText } = prepareCompactionMessage({
+      workspaceId: "ws-1",
+      continueMessage: { text: "fix tests" },
+      sendMessageOptions,
+    });
+
+    expect(messageText).toContain("The user wants to continue with: fix tests");
+  });
+
   test("creates continueMessage when images are provided without text", () => {
     const sendMessageOptions = createBaseOptions();
     const { metadata } = prepareCompactionMessage({

src/browser/utils/chatCommands.ts

@@ -627,7 +627,23 @@ export function prepareCompactionMessage(options: CompactionOptions): {
   // Build compaction message with optional continue context
   let messageText = buildCompactionPrompt(targetWords);
 
-  if (options.continueMessage) {
+  const continueText = options.continueMessage?.text;
+  const hasImages =
+    options.continueMessage?.imageParts && options.continueMessage.imageParts.length > 0;
+  const hasReviews = options.continueMessage?.reviews && options.continueMessage.reviews.length > 0;
+
+  // continueMessage is a follow-up user message that will be auto-sent after compaction.
+  // For forced compaction (no explicit follow-up), we inject a short resume sentinel ("Continue").
+  // Keep that sentinel out of the *compaction prompt* (summarization request), otherwise the model can
+  // misread it as a competing instruction. We still keep it in metadata so the backend resumes.
+  // Only treat it as the default resume when there's no other queued content (images/reviews).
+  const isDefaultResume =
+    typeof continueText === "string" &&
+    continueText.trim() === "Continue" &&
+    !hasImages &&
+    !hasReviews;
+
+  if (options.continueMessage && !isDefaultResume) {
     messageText += `\n\nThe user wants to continue with: ${options.continueMessage.text}`;
   }
 
@@ -636,10 +652,7 @@ export function prepareCompactionMessage(options: CompactionOptions): {
 
   // Create compaction metadata (will be stored in user message)
   // Only include continueMessage if there's text, images, or reviews to queue after compaction
-  const hasText = options.continueMessage?.text;
-  const hasImages =
-    options.continueMessage?.imageParts && options.continueMessage.imageParts.length > 0;
-  const hasReviews = options.continueMessage?.reviews && options.continueMessage.reviews.length > 0;
+  const hasText = continueText;
   const compactData: CompactionRequestData = {
     model: effectiveModel,
     maxOutputTokens: options.maxOutputTokens,