fix: place auto-close caret synchronously on plain contenteditable

src/adapters/chrome/content-script/suggestions/ContentEditableAdapter.ts

@@ -143,6 +143,12 @@ export class ContentEditableAdapter {
       if (shouldTryNativeReplacement) {
         const nativeReplacementResult = this.tryNativeReplacement(elem, replacementText);
         if (nativeReplacementResult.didMutateDom) {
+          // execCommand leaves the caret at the end of the inserted text. Plain
+          // contenteditable has no async host reconciliation to override us, so
+          // place the caret at the final offset synchronously. This prevents a
+          // race where a fast follow-up keystroke (e.g. auto-close "()" then an
+          // immediate "x") lands before a deferred caret correction runs.
+          this.setCaret(editScope, cursorAfter);
           logger.debug("Contenteditable replacement handled by execCommand fallback", {
             didDispatchInput: nativeReplacementResult.didDispatchInput,
             editorTextLength: (elem.textContent ?? "").length,

src/adapters/chrome/content-script/suggestions/SuggestionTextEditService.ts

@@ -706,7 +706,19 @@ export class SuggestionTextEditService {
     // DOM asynchronously via microtask. This means didMutateDom is false at check
     // time even though the edit WILL be applied. The deferred callback validates
     // that the expected text appeared before moving the cursor.
-    if (edit.cursorOffset !== undefined && !TextTargetAdapter.isTextValue(entry.elem)) {
+    //
+    // Plain contenteditable applied via the DOM path ("fallback-dom") already had
+    // its caret placed synchronously at the final offset by the adapter, so skip
+    // the deferred relative move-back there — running it would double-correct the
+    // caret. Only host editors (React via beforeinput, CKEditor via host session)
+    // reconcile asynchronously and still need the deferred reposition.
+    const caretPlacedSynchronously =
+      "appliedBy" in applyResult && applyResult.appliedBy === "fallback-dom";
+    if (
+      edit.cursorOffset !== undefined &&
+      !TextTargetAdapter.isTextValue(entry.elem) &&
+      !caretPlacedSynchronously
+    ) {
       const moveBackCount = replacement.length - edit.cursorOffset;
       if (moveBackCount > 0) {
         const targetElem = entry.elem as HTMLElement;

tests/e2e/full.e2e.test.ts

@@ -6069,7 +6069,9 @@ describeE2E(`Extension E2E Test [${BROWSER_TYPE}]`, () => {
       await typeInInput(page, selector, "hello (");
       await waitForInputContentMatch(page, selector, /^hello \(\)$/, browserTimeout(5000, 9000));
 
-      // Verify cursor position: typing after auto-close should insert between brackets
+      // Verify cursor position: typing after auto-close should insert between
+      // brackets. Plain contenteditable repositions the caret synchronously, so
+      // an immediate keystroke must land inside the brackets (no settle needed).
       await typeInInput(page, selector, "x");
       await waitForInputContentMatch(page, selector, /^hello \(x\)$/, browserTimeout(5000, 9000));