fix(ui): harden issue comment editor sync

ui/src/components/MarkdownEditor.tsx

@@ -364,6 +364,19 @@ export const MarkdownEditor = forwardRef<MarkdownEditorRef, MarkdownEditorProps>
     return map;
   }, [mentions]);
 
+  const setEditorRef = useCallback((instance: MDXEditorMethods | null) => {
+    ref.current = instance;
+    if (!instance) {
+      return;
+    }
+    if (valueRef.current !== latestValueRef.current) {
+      // Re-apply the latest controlled value once MDXEditor exposes its imperative API.
+      echoIgnoreMarkdownRef.current = valueRef.current;
+      instance.setMarkdown(valueRef.current);
+      latestValueRef.current = valueRef.current;
+    }
+  }, []);
+
   const filteredMentions = useMemo<AutocompleteOption[]>(() => {
     if (!mentionState) return [];
     const q = mentionState.query.trim().toLowerCase();
@@ -798,7 +811,7 @@ export const MarkdownEditor = forwardRef<MarkdownEditorRef, MarkdownEditorProps>
       onPasteCapture={handlePasteCapture}
     >
       <MDXEditor
-        ref={ref}
+        ref={setEditorRef}
         markdown={value}
         placeholder={placeholder}
         onChange={(next) => {

ui/src/lib/optimistic-issue-comments.test.ts

@@ -6,6 +6,7 @@ import {
   applyOptimisticIssueCommentUpdate,
   createOptimisticIssueComment,
   flattenIssueCommentPages,
+  getNextIssueCommentPageParam,
   isQueuedIssueComment,
   matchesIssueRef,
   mergeIssueComments,
@@ -171,6 +172,40 @@ describe("optimistic issue comments", () => {
     expect(flattened.map((comment) => comment.id)).toEqual(["comment-1", "comment-2", "comment-3"]);
   });
 
+  it("returns no next page param when the last page is missing", () => {
+    expect(getNextIssueCommentPageParam(undefined, 50)).toBeUndefined();
+  });
+
+  it("returns the oldest id when the last page is full", () => {
+    expect(
+      getNextIssueCommentPageParam(
+        [
+          {
+            id: "comment-2",
+            companyId: "company-1",
+            issueId: "issue-1",
+            authorAgentId: null,
+            authorUserId: "board-1",
+            body: "Second",
+            createdAt: new Date("2026-03-28T14:00:02.000Z"),
+            updatedAt: new Date("2026-03-28T14:00:02.000Z"),
+          },
+          {
+            id: "comment-1",
+            companyId: "company-1",
+            issueId: "issue-1",
+            authorAgentId: null,
+            authorUserId: "board-1",
+            body: "First",
+            createdAt: new Date("2026-03-28T14:00:01.000Z"),
+            updatedAt: new Date("2026-03-28T14:00:01.000Z"),
+          },
+        ],
+        2,
+      ),
+    ).toBe("comment-1");
+  });
+
   it("upserts paged comments without dropping older pages", () => {
     const nextPages = upsertIssueCommentInPages(
       [

ui/src/lib/optimistic-issue-comments.ts

@@ -102,6 +102,14 @@ export function flattenIssueCommentPages(
   return sortIssueComments((pages ?? []).flatMap((page) => page));
 }
 
+export function getNextIssueCommentPageParam(
+  lastPage: ReadonlyArray<IssueComment> | undefined,
+  pageSize: number,
+): string | undefined {
+  if (!lastPage || lastPage.length < pageSize) return undefined;
+  return lastPage[lastPage.length - 1]?.id;
+}
+
 export function upsertIssueComment(
   comments: IssueComment[] | undefined,
   nextComment: IssueComment,

ui/src/pages/IssueDetail.tsx

@@ -36,6 +36,7 @@ import {
   applyOptimisticIssueCommentUpdate,
   createOptimisticIssueComment,
   flattenIssueCommentPages,
+  getNextIssueCommentPageParam,
   isQueuedIssueComment,
   matchesIssueRef,
   mergeIssueComments,
@@ -416,7 +417,7 @@ export function IssueDetail() {
     enabled: !!issueId,
     initialPageParam: null as string | null,
     getNextPageParam: (lastPage) =>
-      lastPage.length === ISSUE_COMMENT_PAGE_SIZE ? lastPage[lastPage.length - 1]?.id : undefined,
+      getNextIssueCommentPageParam(lastPage, ISSUE_COMMENT_PAGE_SIZE),
     placeholderData: keepPreviousData,
   });
   const comments = useMemo(