diff --git a/ui/src/components/CommentThread.tsx b/ui/src/components/CommentThread.tsx
index 8e042acf..0e97f31a 100644
--- a/ui/src/components/CommentThread.tsx
+++ b/ui/src/components/CommentThread.tsx
@@ -46,6 +46,7 @@ interface CommentThreadProps {
   enableReassign?: boolean;
   reassignOptions?: InlineEntityOption[];
   currentAssigneeValue?: string;
+  suggestedAssigneeValue?: string;
   mentions?: MentionOption[];
 }
 
@@ -269,13 +270,15 @@ export function CommentThread({
   enableReassign = false,
   reassignOptions = [],
   currentAssigneeValue = "",
+  suggestedAssigneeValue,
   mentions: providedMentions,
 }: CommentThreadProps) {
   const [body, setBody] = useState("");
   const [reopen, setReopen] = useState(true);
   const [submitting, setSubmitting] = useState(false);
   const [attaching, setAttaching] = useState(false);
-  const [reassignTarget, setReassignTarget] = useState(currentAssigneeValue);
+  const effectiveSuggestedAssigneeValue = suggestedAssigneeValue ?? currentAssigneeValue;
+  const [reassignTarget, setReassignTarget] = useState(effectiveSuggestedAssigneeValue);
   const [highlightCommentId, setHighlightCommentId] = useState<string | null>(null);
   const editorRef = useRef<MarkdownEditorRef>(null);
   const attachInputRef = useRef<HTMLInputElement | null>(null);
@@ -337,8 +340,8 @@ export function CommentThread({
   }, []);
 
   useEffect(() => {
-    setReassignTarget(currentAssigneeValue);
-  }, [currentAssigneeValue]);
+    setReassignTarget(effectiveSuggestedAssigneeValue);
+  }, [effectiveSuggestedAssigneeValue]);
 
   // Scroll to comment when URL hash matches #comment-{id}
   useEffect(() => {
@@ -370,7 +373,7 @@ export function CommentThread({
       setBody("");
       if (draftKey) clearDraft(draftKey);
       setReopen(false);
-      setReassignTarget(currentAssigneeValue);
+      setReassignTarget(effectiveSuggestedAssigneeValue);
     } finally {
       setSubmitting(false);
     }
diff --git a/ui/src/lib/assignees.test.ts b/ui/src/lib/assignees.test.ts
index 1ce22ef7..59822ef6 100644
--- a/ui/src/lib/assignees.test.ts
+++ b/ui/src/lib/assignees.test.ts
@@ -4,6 +4,7 @@ import {
   currentUserAssigneeOption,
   formatAssigneeUserLabel,
   parseAssigneeValue,
+  suggestedCommentAssigneeValue,
 } from "./assignees";
 
 describe("assignee selection helpers", () => {
@@ -50,4 +51,27 @@ describe("assignee selection helpers", () => {
     expect(formatAssigneeUserLabel("local-board", "someone-else")).toBe("Board");
     expect(formatAssigneeUserLabel("user-abcdef", "someone-else")).toBe("user-");
   });
+
+  it("suggests the last non-me commenter without changing the actual assignee encoding", () => {
+    expect(
+      suggestedCommentAssigneeValue(
+        { assigneeUserId: "board-user" },
+        [
+          { authorUserId: "board-user" },
+          { authorAgentId: "agent-123" },
+        ],
+        "board-user",
+      ),
+    ).toBe("agent:agent-123");
+  });
+
+  it("falls back to the actual assignee when there is no better commenter hint", () => {
+    expect(
+      suggestedCommentAssigneeValue(
+        { assigneeUserId: "board-user" },
+        [{ authorUserId: "board-user" }],
+        "board-user",
+      ),
+    ).toBe("user:board-user");
+  });
 });
diff --git a/ui/src/lib/assignees.ts b/ui/src/lib/assignees.ts
index 274bcd40..c4df80a3 100644
--- a/ui/src/lib/assignees.ts
+++ b/ui/src/lib/assignees.ts
@@ -9,12 +9,40 @@ export interface AssigneeOption {
   searchText?: string;
 }
 
+interface CommentAssigneeSuggestionInput {
+  assigneeAgentId?: string | null;
+  assigneeUserId?: string | null;
+}
+
+interface CommentAssigneeSuggestionComment {
+  authorAgentId?: string | null;
+  authorUserId?: string | null;
+}
+
 export function assigneeValueFromSelection(selection: Partial<AssigneeSelection>): string {
   if (selection.assigneeAgentId) return `agent:${selection.assigneeAgentId}`;
   if (selection.assigneeUserId) return `user:${selection.assigneeUserId}`;
   return "";
 }
 
+export function suggestedCommentAssigneeValue(
+  issue: CommentAssigneeSuggestionInput,
+  comments: CommentAssigneeSuggestionComment[] | null | undefined,
+  currentUserId: string | null | undefined,
+): string {
+  if (comments && comments.length > 0 && currentUserId) {
+    for (let i = comments.length - 1; i >= 0; i--) {
+      const comment = comments[i];
+      if (comment.authorAgentId) return assigneeValueFromSelection({ assigneeAgentId: comment.authorAgentId });
+      if (comment.authorUserId && comment.authorUserId !== currentUserId) {
+        return assigneeValueFromSelection({ assigneeUserId: comment.authorUserId });
+      }
+    }
+  }
+
+  return assigneeValueFromSelection(issue);
+}
+
 export function parseAssigneeValue(value: string): AssigneeSelection {
   if (!value) {
     return { assigneeAgentId: null, assigneeUserId: null };
diff --git a/ui/src/pages/IssueDetail.tsx b/ui/src/pages/IssueDetail.tsx
index e90965f6..fbed1e9c 100644
--- a/ui/src/pages/IssueDetail.tsx
+++ b/ui/src/pages/IssueDetail.tsx
@@ -11,6 +11,7 @@ import { useCompany } from "../context/CompanyContext";
 import { usePanel } from "../context/PanelContext";
 import { useToast } from "../context/ToastContext";
 import { useBreadcrumbs } from "../context/BreadcrumbContext";
+import { assigneeValueFromSelection, suggestedCommentAssigneeValue } from "../lib/assignees";
 import { queryKeys } from "../lib/queryKeys";
 import { readIssueDetailBreadcrumb } from "../lib/issueDetailBreadcrumb";
 import { useProjectOrder } from "../hooks/useProjectOrder";
@@ -374,21 +375,15 @@ export function IssueDetail() {
     return options;
   }, [agents, currentUserId]);
 
-  const currentAssigneeValue = useMemo(() => {
-    // Default to the last commenter who is not "me" so the user doesn't
-    // accidentally reassign to themselves when commenting on their own issue.
-    if (comments && comments.length > 0 && currentUserId) {
-      for (let i = comments.length - 1; i >= 0; i--) {
-        const c = comments[i];
-        if (c.authorAgentId) return `agent:${c.authorAgentId}`;
-        if (c.authorUserId && c.authorUserId !== currentUserId)
-          return `user:${c.authorUserId}`;
-      }
-    }
-    if (issue?.assigneeAgentId) return `agent:${issue.assigneeAgentId}`;
-    if (issue?.assigneeUserId) return `user:${issue.assigneeUserId}`;
-    return "";
-  }, [issue?.assigneeAgentId, issue?.assigneeUserId, comments, currentUserId]);
+  const actualAssigneeValue = useMemo(
+    () => assigneeValueFromSelection(issue ?? {}),
+    [issue],
+  );
+
+  const suggestedAssigneeValue = useMemo(
+    () => suggestedCommentAssigneeValue(issue ?? {}, comments, currentUserId),
+    [issue, comments, currentUserId],
+  );
 
   const commentsWithRunMeta = useMemo(() => {
     const runMetaByCommentId = new Map<string, { runId: string; runAgentId: string | null }>();
@@ -1011,7 +1006,8 @@ export function IssueDetail() {
             draftKey={`paperclip:issue-comment-draft:${issue.id}`}
             enableReassign
             reassignOptions={commentReassignOptions}
-            currentAssigneeValue={currentAssigneeValue}
+            currentAssigneeValue={actualAssigneeValue}
+            suggestedAssigneeValue={suggestedAssigneeValue}
             mentions={mentionOptions}
             onAdd={async (body, reopen, reassignment) => {
               if (reassignment) {