diff --git a/packages/core/src/comments/anchors.ts b/packages/core/src/comments/anchors.ts
index 99c1bc6ba5..57e6293fd4 100644
--- a/packages/core/src/comments/anchors.ts
+++ b/packages/core/src/comments/anchors.ts
@@ -59,6 +59,9 @@ export type CommentAnchor = z.infer<typeof commentAnchorSchema>;
 export const commentContextSchema = z.object({
   anchor: commentAnchorSchema,
   threadState: z.enum(["resolved", "open"]).optional(),
+  // The task the commented resource belongs to. Artifact and canvas ids live in a run's
+  // JSON rather than a table, so the server can't get back to the task without being told.
+  taskId: z.string().optional(),
 });
 
 export type CommentContext = z.infer<typeof commentContextSchema>;
diff --git a/packages/ui/src/features/canvas/components/TaskCommentsList.tsx b/packages/ui/src/features/canvas/components/TaskCommentsList.tsx
index 19d64f7c68..51c34d4984 100644
--- a/packages/ui/src/features/canvas/components/TaskCommentsList.tsx
+++ b/packages/ui/src/features/canvas/components/TaskCommentsList.tsx
@@ -123,6 +123,7 @@ function ResourceThreadRow({
   thread,
   source,
   root,
+  taskId,
   members,
   selected,
   pulsing,
@@ -132,13 +133,14 @@ function ResourceThreadRow({
   thread: TaskCommentThread;
   source: CommentSource;
   root: ResourceComment;
+  taskId: string;
   members: UserBasic[];
   selected: boolean;
   pulsing: boolean;
   resolution?: HighlightResolution;
   onOpen: () => void;
 }) {
-  const createComment = useCreateComment(source.target);
+  const createComment = useCreateComment(source.target, taskId);
   const setResolved = useSetCommentResolved(source.target);
 
   return (
@@ -278,7 +280,7 @@ export function TaskCommentsList({
 
   const taskTarget = useMemo(() => taskCommentTarget(task.id), [task.id]);
   const taskSourceKey = commentTargetKey(taskTarget);
-  const createTaskComment = useCreateComment(taskTarget);
+  const createTaskComment = useCreateComment(taskTarget, task.id);
 
   const threads = useMemo(() => {
     const reviewByUrl = new Map(prReviews.byUrl);
@@ -531,6 +533,7 @@ export function TaskCommentsList({
                 thread={thread}
                 source={thread.origin.source}
                 root={thread.origin.root}
+                taskId={task.id}
                 members={members}
                 selected={thread.id === focusedThreadId}
                 pulsing={thread.id === pulseThreadId}
diff --git a/packages/ui/src/features/sessions/components/ArtifactPreview.tsx b/packages/ui/src/features/sessions/components/ArtifactPreview.tsx
index 2a9a1fe6ec..96c9c43394 100644
--- a/packages/ui/src/features/sessions/components/ArtifactPreview.tsx
+++ b/packages/ui/src/features/sessions/components/ArtifactPreview.tsx
@@ -108,7 +108,7 @@ export function ArtifactPreview({
   );
   const commentsQuery = useCommentsQuery(commentTarget);
   const { members } = useOrgMembers();
-  const createComment = useCreateComment(commentTarget);
+  const createComment = useCreateComment(commentTarget, taskId);
   const requestCommentFocus = useCommentNavigationStore(
     (state) => state.requestCommentFocus,
   );
diff --git a/packages/ui/src/features/sessions/components/useComments.ts b/packages/ui/src/features/sessions/components/useComments.ts
index 21b9d08637..874b7feeb4 100644
--- a/packages/ui/src/features/sessions/components/useComments.ts
+++ b/packages/ui/src/features/sessions/components/useComments.ts
@@ -133,15 +133,26 @@ export function useCommentsForTargetsQuery(
   });
 }
 
-export function useCreateComment(target: CommentTarget) {
+/**
+ * @param taskId Names the task the resource belongs to, so a mention on it reaches that
+ * task's activity feed — the server can't resolve an artifact or canvas id back to a task.
+ */
+export function useCreateComment(target: CommentTarget, taskId?: string) {
   const service = useService<SessionService>(SESSION_SERVICE);
   const queryClient = useQueryClient();
   const caches = commentCachesCoveringTarget(target);
+  const contextWithTask = (context: unknown) =>
+    taskId ? { ...(context as Record<string, unknown>), taskId } : context;
 
   return useMutation({
     mutationFn: (
       request: Omit<CreateResourceCommentRequest, "scope" | "itemId">,
-    ) => service.createResourceComment({ ...request, ...target }),
+    ) =>
+      service.createResourceComment({
+        ...request,
+        ...target,
+        context: contextWithTask(request.context),
+      }),
     onMutate: async (request) => {
       await queryClient.cancelQueries(caches);
       const previous = queryClient.getQueriesData<ResourceComment[]>(caches);
@@ -151,7 +162,7 @@ export function useCreateComment(target: CommentTarget) {
         content: request.content,
         created_at: new Date().toISOString(),
         item_id: target.itemId,
-        item_context: request.context,
+        item_context: contextWithTask(request.context),
         scope: target.scope,
         source_comment: request.sourceCommentId ?? null,
         completed_at: null,