Fix duplicate comment threads in diff editor

Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

Author: Copilot

src/view/pullRequestCommentController.ts

@@ -230,6 +230,17 @@ export class PullRequestCommentController extends CommentControllerBase implemen
 	private async onDidChangeReviewThreads(e: ReviewThreadChangeEvent): Promise<void> {
 		for (const thread of e.added) {
 			const fileName = thread.path;
+			const key = this.getCommentThreadCacheKey(thread.path, thread.diffSide === DiffSide.LEFT);
+
+			// Defensive: if a comment thread for this review thread id already exists in the cache
+			// (e.g. because addThreadsForEditors already created it from the cache before this event was
+			// processed), update it in place instead of creating a duplicate VS Code comment thread.
+			const existing = this._commentThreadCache[key]?.find(t => t.gitHubThreadId === thread.id);
+			if (existing) {
+				updateThread(this._context, existing, thread, this._githubRepositories);
+				continue;
+			}
+
 			const index = this._pendingCommentThreadAdds.findIndex(t => {
 				const samePath = this._folderRepoManager.gitRelativeRootPath(t.uri.path) === thread.path;
 				const sameLine = (t.range === undefined && thread.subjectType === SubjectType.FILE) || (t.range && t.range.end.line + 1 === thread.endLine);
@@ -270,9 +281,8 @@ export class PullRequestCommentController extends CommentControllerBase implemen
 			}
 
 			if (!newThread) {
-				return;
+				continue;
 			}
-			const key = this.getCommentThreadCacheKey(thread.path, thread.diffSide === DiffSide.LEFT);
 			if (this._commentThreadCache[key]) {
 				this._commentThreadCache[key].push(newThread);
 			} else {

src/view/reviewCommentController.ts

@@ -280,6 +280,17 @@ export class ReviewCommentController extends CommentControllerBase implements Co
 				for (const thread of e.added) {
 					const { path } = thread;
 
+					// Defensive: if a comment thread for this review thread id already exists in any of the
+					// thread maps (e.g. because doInitializeCommentThreads already created it from the cache
+					// before this event was processed), update it in place instead of creating a duplicate
+					// VS Code comment thread.
+					const existingMatch = this._findMatchingThread(thread);
+					if (existingMatch.index > -1) {
+						const matchingThread = existingMatch.threadMap[thread.path][existingMatch.index];
+						updateThread(this._context, matchingThread, thread, githubRepositories);
+						continue;
+					}
+
 					const index = await arrayFindIndexAsync(this._pendingCommentThreadAdds, async t => {
 						const fileName = this._folderRepoManager.gitRelativeRootPath(t.uri.path);
 						if (fileName !== thread.path) {