fix(amazonq): block completion before active edit is accepted/rejected (#8141)

## Problem
Both completion suggestions (ghost text) and edit suggestions (diff
view) could appear simultaneously due to a race condition. The
EditSuggestionState flag was set too late in the edit display flow,
allowing completion requests to check the state, see it as false, and
proceed even while an edit was being displayed.

## Solution
Fixed the race condition by setting the edit state immediately at the
start of displaySvgDecoration() before any async operations:

* Set EditSuggestionState to true at the beginning of the edit flow
* Add state cleanup when edit cannot be shown (completion already active
or invalid patch)
* Avoid calling clearDecorations() in displayEditSuggestion() to prevent
premature state reset
* Check EditSuggestionState before making completion requests in
recommendationService.ts.

This ensures only one suggestion type is displayed at a time with proper
mutual exclusion.

---

- Treat all work as PUBLIC. Private `feature/x` branches will not be
squash-merged at release time.
- Your code changes must meet the guidelines in
[CONTRIBUTING.md](https://github.com/aws/aws-toolkit-vscode/blob/master/CONTRIBUTING.md#guidelines).
- License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

Author: bywang56

packages/amazonq/src/app/inline/EditRendering/displayImage.ts

@@ -136,10 +136,11 @@ export class EditDecorationManager {
         newCode: string,
         originalCodeHighlightRanges: Array<{ line: number; start: number; end: number }>
     ): Promise<void> {
-        await this.clearDecorations(editor)
-
-        await setContext('aws.amazonq.editSuggestionActive' as any, true)
-        EditSuggestionState.setEditSuggestionActive(true)
+        // Clear old decorations but don't reset state (state is already set in displaySvgDecoration)
+        editor.setDecorations(this.imageDecorationType, [])
+        editor.setDecorations(this.removedCodeDecorationType, [])
+        this.currentImageDecoration = undefined
+        this.currentRemovedCodeDecorations = []
 
         this.acceptHandler = onAccept
         this.rejectHandler = onReject
@@ -313,8 +314,16 @@ export async function displaySvgDecoration(
 ) {
     const originalCode = editor.document.getText()
 
+    // Set edit state immediately to prevent race condition with completion requests
+    await setContext('aws.amazonq.editSuggestionActive' as any, true)
+    EditSuggestionState.setEditSuggestionActive(true)
+
     // Check if a completion suggestion is currently active - if so, discard edit suggestion
     if (inlineCompletionProvider && (await inlineCompletionProvider.isCompletionActive())) {
+        // Clean up state since we're not showing the edit
+        await setContext('aws.amazonq.editSuggestionActive' as any, false)
+        EditSuggestionState.setEditSuggestionActive(false)
+
         // Emit DISCARD telemetry for edit suggestion that can't be shown due to active completion
         const params = createDiscardTelemetryParams(session, item)
         languageClient.sendNotification('aws/logInlineCompletionSessionResults', params)
@@ -326,6 +335,10 @@ export async function displaySvgDecoration(
 
     const isPatchValid = applyPatch(editor.document.getText(), item.insertText as string)
     if (!isPatchValid) {
+        // Clean up state since we're not showing the edit
+        await setContext('aws.amazonq.editSuggestionActive' as any, false)
+        EditSuggestionState.setEditSuggestionActive(false)
+
         const params = createDiscardTelemetryParams(session, item)
         // TODO: this session is closed on flare side hence discarded is not emitted in flare
         languageClient.sendNotification('aws/logInlineCompletionSessionResults', params)

packages/amazonq/src/app/inline/recommendationService.ts

@@ -138,7 +138,7 @@ export class RecommendationService {
              * Completions use PartialResultToken with single 1 call of [getAllRecommendations].
              * Edits leverage partialResultToken to achieve EditStreak such that clients can pull all continuous suggestions generated by the model within 1 EOS block.
              */
-            if (!isTriggerByDeletion && !request.partialResultToken) {
+            if (!isTriggerByDeletion && !request.partialResultToken && !EditSuggestionState.isEditSuggestionActive()) {
                 const completionPromise: Promise<InlineCompletionListWithReferences> = languageClient.sendRequest(
                     inlineCompletionWithReferencesRequestType.method,
                     request,

packages/amazonq/test/unit/amazonq/apps/inline/recommendationService.test.ts

@@ -333,7 +333,7 @@ describe('RecommendationService', () => {
             }
         })
 
-        it('should make completion request when edit suggestion is active', async () => {
+        it('should not make completion request when edit suggestion is active', async () => {
             // Mock EditSuggestionState to return true (edit suggestion is active)
             sandbox.stub(EditSuggestionState, 'isEditSuggestionActive').returns(true)
 
@@ -360,13 +360,15 @@ describe('RecommendationService', () => {
             const completionCalls = cs.filter((c) => c.firstArg === completionApi)
             const editCalls = cs.filter((c) => c.firstArg === editApi)
 
-            assert.strictEqual(cs.length, 2) // Only edit call
-            assert.strictEqual(completionCalls.length, 1) // No completion calls
+            assert.strictEqual(cs.length, 1) // Only edit call
+            assert.strictEqual(completionCalls.length, 0) // No completion calls
             assert.strictEqual(editCalls.length, 1) // One edit call
         })
 
         it('should make completion request when edit suggestion is not active', async () => {
             // Mock EditSuggestionState to return false (no edit suggestion active)
+            sandbox.stub(EditSuggestionState, 'isEditSuggestionActive').returns(false)
+
             const mockResult = {
                 sessionId: 'test-session',
                 items: [mockInlineCompletionItemOne],