Fix duplicate rich-editor Tab suggestion inserts

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

@@ -53,6 +53,7 @@ export class SuggestionEntrySession {
   private readonly insertSpaceAfterAutocomplete: boolean;
   private readonly logRenderedSuggestionPopup: SuggestionEntrySessionOptions["logRenderedSuggestionPopup"];
   private readonly logNoVisibleSuggestions: (context: PredictionResponse) => void;
+  private lastAcceptedSuggestion: string | null = null;
 
   constructor(options: SuggestionEntrySessionOptions) {
     this.entry = options.entry;
@@ -1188,12 +1189,21 @@ export class SuggestionEntrySession {
   }
 
   private acceptSuggestionInternal(suggestion: string): boolean {
+    if (
+      this.lastAcceptedSuggestion === suggestion &&
+      this.entry.suppressNextSuggestionInputPrediction &&
+      this.entry.pendingExtensionEdit?.source === "suggestion"
+    ) {
+      return false;
+    }
+
     this.entry.suppressNextSuggestionInputPrediction = true;
     const accepted = this.textEditService.acceptSuggestion(this.entry, suggestion);
     if (!accepted) {
       this.entry.suppressNextSuggestionInputPrediction = false;
       return false;
     }
+    this.lastAcceptedSuggestion = suggestion;
     this.finishAcceptedSuggestion(
       accepted.triggerText,
       accepted.insertedText,
@@ -1292,6 +1302,7 @@ export class SuggestionEntrySession {
   }
 
   private clearAcceptedSuggestionTransientState(): void {
+    this.lastAcceptedSuggestion = null;
     this.clearPendingExtensionEdit();
     this.entry.missingTrailingSpace = false;
     this.entry.expectedCursorPos = 0;

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

@@ -1071,29 +1071,7 @@ export class SuggestionTextEditService {
       cursorAfter,
       { scopeRoot: activeBlock },
     );
-    const deferredHostNoMutation =
-      "appliedBy" in initialApplyResult &&
-      initialApplyResult.appliedBy === "host-beforeinput" &&
-      !initialApplyResult.didMutateDom;
-
-    if (!deferredHostNoMutation) {
-      return initialApplyResult;
-    }
-
-    const domFallbackResult = this.replaceTextByOffsets(
-      elem,
-      blockSourceText,
-      replaceStart,
-      replaceEnd,
-      replacementText,
-      cursorAfter,
-      {
-        preferDomMutation: true,
-        scopeRoot: activeBlock,
-      },
-    );
-
-    return domFallbackResult.didMutateDom ? domFallbackResult : initialApplyResult;
+    return initialApplyResult;
   }
 
   private acceptContentEditableSuggestion(

tests/SuggestionEntrySession.test.ts

@@ -533,6 +533,49 @@ test("session ignores stale prediction responses after suggestion acceptance", (
   expect(renderMenu).not.toHaveBeenCalled();
 });
 
+test("session ignores an immediate duplicate suggestion accept while the first accepted edit is still pending", () => {
+  const editable = document.createElement("div");
+  editable.setAttribute("contenteditable", "true");
+  Object.defineProperty(editable, "isContentEditable", { value: true, configurable: true });
+
+  const entry = createSuggestionEntry({
+    elem: editable as SuggestionEntry["elem"],
+    requestId: 2,
+    suggestions: ["beta"],
+    latestMentionText: "bet",
+  });
+  const textEditService = {
+    acceptSuggestion: jest.fn(() => {
+      entry.pendingExtensionEdit = {
+        replaceStart: 0,
+        originalText: "bet",
+        replacementText: "beta",
+        cursorBefore: 3,
+        cursorAfter: 4,
+        postEditFingerprint: {
+          fullText: "beta",
+          cursorOffset: 4,
+          selectionCollapsed: true,
+        },
+        source: "suggestion",
+      };
+      return {
+        triggerText: "bet",
+        insertedText: "beta",
+        cursorAfter: 4,
+        cursorAfterIsBlockLocal: false,
+      };
+    }),
+    applyGrammarEdit: jest.fn(() => ({ applied: false, didDispatchInput: false })),
+    syncManualAutoFixSuppression: jest.fn(),
+  };
+  const session = makeSession({ entry, textEditService });
+
+  expect(session.acceptSuggestionAtIndex(0)).toBe(true);
+  expect(session.acceptSuggestionAtIndex(0)).toBe(false);
+  expect(textEditService.acceptSuggestion).toHaveBeenCalledTimes(1);
+});
+
 test("session suppresses the synthetic input emitted by accepted suggestions", () => {
   const clearPendingFallback = jest.fn();
   const predictionCoordinator = {

tests/SuggestionTextEditService.test.ts

@@ -1264,7 +1264,7 @@ describe("SuggestionTextEditService", () => {
     expect(editable.textContent).toBe("Wh");
   });
 
-  test("retries generic contenteditable acceptance with direct DOM mutation after a canceled no-op beforeinput", () => {
+  test("keeps generic contenteditable acceptance deferred when beforeinput is canceled without immediate DOM mutation", () => {
     const service = new SuggestionTextEditService({
       findMentionToken,
       isSeparator: (value) => /\s/.test(value),
@@ -1297,7 +1297,7 @@ describe("SuggestionTextEditService", () => {
       cursorAfter: 5,
       cursorAfterIsBlockLocal: true,
     });
-    expect(editable.textContent).toBe("What\u00A0");
+    expect(editable.textContent).toBe("Wh");
     expect(entry.pendingExtensionEdit?.awaitingHostInputEcho).toBe(true);
   });