diff --git a/ui/src/components/TaskChatThread.tsx b/ui/src/components/TaskChatThread.tsx
index 0a41b36d387..e373d9ed886 100644
--- a/ui/src/components/TaskChatThread.tsx
+++ b/ui/src/components/TaskChatThread.tsx
@@ -18,7 +18,8 @@ import { TaskChatInteractionCard } from "@/components/task-chat/TaskChatInteract
 import { TaskChatThreadView } from "@/components/task-chat/TaskChatThreadView";
 import { TaskChatComposer } from "@/components/task-chat/TaskChatComposer";
 import { useIssuePlanDocument } from "@/hooks/useIssuePlanDocument";
-import { latestSameRunHandoffTimestamp } from "@/lib/issue-chat-messages";
+import { latestSameRunHandoffTimestamp, type IssueChatComment } from "@/lib/issue-chat-messages";
+import { workModeInEffectAt } from "@/lib/issue-timeline-events";
 import { workModeMetaFor } from "@/lib/work-mode-meta";
 
 function toMs(value: Date | string | null | undefined): number {
@@ -85,12 +86,30 @@ export function TaskChatThread(props: TaskChatThreadProps) {
     onSubmitInteractionVerdicts,
     externalReferences,
     threadHeader,
+    workModeChanges,
   } = props;
 
-  const agentModeLabel = workModeMetaFor(issueWorkMode).label;
+  const linkedRunMetaById = useMemo(() => {
+    const map = new Map<string, NonNullable<TaskChatThreadProps["linkedRuns"]>[number]>();
+    for (const run of linkedRuns ?? []) map.set(run.runId, run);
+    return map;
+  }, [linkedRuns]);
+
+  // Each agent reply is tagged with the mode its request ran under: the
+  // issue's work mode at the reply's run start (comment.runId linkage),
+  // reconstructed from the activity feed's work-mode switch history — not the
+  // issue's current mode, which the user may have changed since.
+  const agentModeLabelFor = useCallback(
+    (comment: IssueChatComment) => {
+      const runMeta = comment.runId ? linkedRunMetaById.get(comment.runId) : undefined;
+      const atMs = toMs(runMeta?.startedAt ?? runMeta?.createdAt ?? comment.createdAt);
+      return workModeMetaFor(workModeInEffectAt(workModeChanges ?? [], atMs, issueWorkMode)).label;
+    },
+    [linkedRunMetaById, workModeChanges, issueWorkMode],
+  );
   const commentItems = useMemo(
-    () => commentsToTaskChatItems(comments, { agentMap, userLabelMap, currentUserId, agentModeLabel }),
-    [comments, agentMap, userLabelMap, currentUserId, agentModeLabel],
+    () => commentsToTaskChatItems(comments, { agentMap, userLabelMap, currentUserId, agentModeLabelFor }),
+    [comments, agentMap, userLabelMap, currentUserId, agentModeLabelFor],
   );
 
   // Every run we might need a transcript for (history + live), deduped by id.
@@ -162,12 +181,6 @@ export function TaskChatThread(props: TaskChatThreadProps) {
     return map;
   }, [comments]);
 
-  const linkedRunMetaById = useMemo(() => {
-    const map = new Map<string, NonNullable<TaskChatThreadProps["linkedRuns"]>[number]>();
-    for (const run of linkedRuns ?? []) map.set(run.runId, run);
-    return map;
-  }, [linkedRuns]);
-
   const { data: planDocument } = useIssuePlanDocument(issueId);
 
   // Comments, interactions, and the plan-doc marker merged into one
diff --git a/ui/src/components/task-chat/task-chat-adapter.ts b/ui/src/components/task-chat/task-chat-adapter.ts
index 106cfc634fc..e77036ffd07 100644
--- a/ui/src/components/task-chat/task-chat-adapter.ts
+++ b/ui/src/components/task-chat/task-chat-adapter.ts
@@ -17,10 +17,10 @@ export interface TaskChatAdapterContext {
   currentUserId?: string | null;
   /**
    * Capitalized mode chip for agent-authored bubbles ("Agent mode" / "Plan
-   * mode" / "Ask mode") — the issue's work mode at render time (per-comment
-   * mode attribution is Tier-B, out of scope here).
+   * mode" / "Ask mode") — resolved per comment, so each reply is tagged with
+   * the mode its request actually ran under (not the issue's current mode).
    */
-  agentModeLabel?: string;
+  agentModeLabelFor?: (comment: IssueChatComment) => string | undefined;
 }
 
 function effectiveAgentId(comment: IssueChatComment): string | null {
@@ -74,7 +74,7 @@ export function commentsToTaskChatItems(
       timestamp: formatTimestamp(comment.createdAt),
       optimistic,
       agentIcon,
-      modeLabel: kind === "agent" ? ctx.agentModeLabel : undefined,
+      modeLabel: kind === "agent" ? ctx.agentModeLabelFor?.(comment) : undefined,
     });
   }
   return items;
diff --git a/ui/src/pages/IssueDetail.tsx b/ui/src/pages/IssueDetail.tsx
index ee73e650313..09c82413d85 100644
--- a/ui/src/pages/IssueDetail.tsx
+++ b/ui/src/pages/IssueDetail.tsx
@@ -26,7 +26,7 @@ import { useToastActions } from "../context/ToastContext";
 import { useBreadcrumbs } from "../context/BreadcrumbContext";
 import { assigneeValueFromSelection, formatAssigneeUserLabel, formatUserLabel, suggestedCommentAssigneeValue } from "../lib/assignees";
 import { buildCompanyUserInlineOptions, buildCompanyUserLabelMap, buildCompanyUserProfileMap, buildMarkdownMentionOptions, isAgentTaskTarget } from "../lib/company-members";
-import { extractIssueTimelineEvents } from "../lib/issue-timeline-events";
+import { extractIssueTimelineEvents, extractIssueWorkModeChanges } from "../lib/issue-timeline-events";
 import { queryKeys } from "../lib/queryKeys";
 import { keepPreviousDataForSameQueryTail } from "../lib/query-placeholder-data";
 import { collectLiveIssueIds } from "../lib/liveIssueIds";
@@ -1176,6 +1176,10 @@ const IssueDetailChatTab = memo(function IssueDetailChatTab({
     () => extractIssueTimelineEvents(resolvedActivity),
     [resolvedActivity],
   );
+  const workModeChanges = useMemo(
+    () => extractIssueWorkModeChanges(resolvedActivity),
+    [resolvedActivity],
+  );
 
   const loadOlderButton = hasOlderComments ? (
     <div className="flex justify-center">
@@ -1214,6 +1218,7 @@ const IssueDetailChatTab = memo(function IssueDetailChatTab({
         feedbackTermsUrl={feedbackTermsUrl}
         linkedRuns={timelineRuns}
         timelineEvents={timelineEvents}
+        workModeChanges={workModeChanges}
         liveRuns={resolvedLiveRuns}
         activeRun={resolvedActiveRun}
         issueId={issueId}
@@ -4197,7 +4202,11 @@ export function IssueDetail() {
             </Badge>
           ) : null}
 
-          {issue.workMode === "ask" || issue.workMode === "planning" ? (() => {
+          {/* Task Chat Redesign: no mode chip in the header — mode is a
+              per-request choice made in the composer, and each agent reply
+              carries its own mode chip; a header chip would misread as a
+              task-global setting. Flag OFF keeps the legacy badge. */}
+          {!taskChatShellEnabled && (issue.workMode === "ask" || issue.workMode === "planning") ? (() => {
             const workModeMeta = workModeMetaFor(issue.workMode);
             const WorkModeIcon = workModeMeta.icon;
             return (