diff --git a/packages/shared/src/types/issue.ts b/packages/shared/src/types/issue.ts
index d55f8e15..9ef7f2d4 100644
--- a/packages/shared/src/types/issue.ts
+++ b/packages/shared/src/types/issue.ts
@@ -143,6 +143,7 @@ export interface Issue {
   mentionedProjects?: Project[];
   myLastTouchAt?: Date | null;
   lastExternalCommentAt?: Date | null;
+  lastActivityAt?: Date | null;
   isUnreadForMe?: boolean;
   createdAt: Date;
   updatedAt: Date;
diff --git a/ui/src/lib/inbox.test.ts b/ui/src/lib/inbox.test.ts
index 2cdd8721..784e38cb 100644
--- a/ui/src/lib/inbox.test.ts
+++ b/ui/src/lib/inbox.test.ts
@@ -180,6 +180,7 @@ function makeIssue(id: string, isUnreadForMe: boolean): Issue {
     labelIds: [],
     myLastTouchAt: new Date("2026-03-11T00:00:00.000Z"),
     lastExternalCommentAt: new Date("2026-03-11T01:00:00.000Z"),
+    lastActivityAt: new Date("2026-03-11T01:00:00.000Z"),
     isUnreadForMe,
   };
 }
@@ -357,10 +358,10 @@ describe("inbox helpers", () => {
 
   it("mixes approvals into the inbox feed by most recent activity", () => {
     const newerIssue = makeIssue("1", true);
-    newerIssue.lastExternalCommentAt = new Date("2026-03-11T04:00:00.000Z");
+    newerIssue.lastActivityAt = new Date("2026-03-11T04:00:00.000Z");
 
     const olderIssue = makeIssue("2", false);
-    olderIssue.lastExternalCommentAt = new Date("2026-03-11T02:00:00.000Z");
+    olderIssue.lastActivityAt = new Date("2026-03-11T02:00:00.000Z");
 
     const approval = makeApprovalWithTimestamps(
       "approval-between",
@@ -385,19 +386,21 @@ describe("inbox helpers", () => {
     ]);
   });
 
-  it("sorts touched issues by latest external comment timestamp", () => {
-    const newerIssue = makeIssue("1", true);
-    newerIssue.lastExternalCommentAt = new Date("2026-03-11T05:00:00.000Z");
+  it("prefers canonical lastActivityAt over comment-only timestamps", () => {
+    const activityIssue = makeIssue("1", true);
+    activityIssue.lastExternalCommentAt = new Date("2026-03-11T01:00:00.000Z");
+    activityIssue.lastActivityAt = new Date("2026-03-11T05:00:00.000Z");
 
-    const olderIssue = makeIssue("2", true);
-    olderIssue.lastExternalCommentAt = new Date("2026-03-11T04:00:00.000Z");
+    const commentIssue = makeIssue("2", true);
+    commentIssue.lastExternalCommentAt = new Date("2026-03-11T04:00:00.000Z");
+    commentIssue.lastActivityAt = new Date("2026-03-11T04:00:00.000Z");
 
-    expect(getRecentTouchedIssues([olderIssue, newerIssue]).map((issue) => issue.id)).toEqual(["1", "2"]);
+    expect(getRecentTouchedIssues([commentIssue, activityIssue]).map((issue) => issue.id)).toEqual(["1", "2"]);
   });
 
   it("mixes join requests into the inbox feed by most recent activity", () => {
     const issue = makeIssue("1", true);
-    issue.lastExternalCommentAt = new Date("2026-03-11T04:00:00.000Z");
+    issue.lastActivityAt = new Date("2026-03-11T04:00:00.000Z");
 
     const joinRequest = makeJoinRequest("join-1");
     joinRequest.createdAt = new Date("2026-03-11T03:00:00.000Z");
@@ -482,7 +485,7 @@ describe("inbox helpers", () => {
   it("limits recent touched issues before unread badge counting", () => {
     const issues = Array.from({ length: RECENT_ISSUES_LIMIT + 5 }, (_, index) => {
       const issue = makeIssue(String(index + 1), index < 3);
-      issue.lastExternalCommentAt = new Date(Date.UTC(2026, 2, 31, 0, 0, 0, 0) - index * 60_000);
+      issue.lastActivityAt = new Date(Date.UTC(2026, 2, 31, 0, 0, 0, 0) - index * 60_000);
       return issue;
     });
 
diff --git a/ui/src/lib/inbox.ts b/ui/src/lib/inbox.ts
index 647b6bea..9f26e998 100644
--- a/ui/src/lib/inbox.ts
+++ b/ui/src/lib/inbox.ts
@@ -217,6 +217,9 @@ export function normalizeTimestamp(value: string | Date | null | undefined): num
 }
 
 export function issueLastActivityTimestamp(issue: Issue): number {
+  const lastActivityAt = normalizeTimestamp(issue.lastActivityAt);
+  if (lastActivityAt > 0) return lastActivityAt;
+
   const lastExternalCommentAt = normalizeTimestamp(issue.lastExternalCommentAt);
   if (lastExternalCommentAt > 0) return lastExternalCommentAt;
 
diff --git a/ui/src/pages/Inbox.test.tsx b/ui/src/pages/Inbox.test.tsx
index 10ac47d7..adb161c2 100644
--- a/ui/src/pages/Inbox.test.tsx
+++ b/ui/src/pages/Inbox.test.tsx
@@ -56,6 +56,7 @@ function createIssue(overrides: Partial<Issue> = {}): Issue {
     labelIds: [],
     myLastTouchAt: null,
     lastExternalCommentAt: null,
+    lastActivityAt: new Date("2026-03-11T00:00:00.000Z"),
     isUnreadForMe: false,
     ...overrides,
   };
diff --git a/ui/src/pages/Inbox.tsx b/ui/src/pages/Inbox.tsx
index d8bbccfa..b0898f40 100644
--- a/ui/src/pages/Inbox.tsx
+++ b/ui/src/pages/Inbox.tsx
@@ -214,7 +214,7 @@ export function InboxIssueMetaLeading({
 }
 
 function issueActivityText(issue: Issue): string {
-  return `Updated ${timeAgo(issue.lastExternalCommentAt ?? issue.updatedAt)}`;
+  return `Updated ${timeAgo(issue.lastActivityAt ?? issue.lastExternalCommentAt ?? issue.updatedAt)}`;
 }
 
 function issueTrailingGridTemplate(columns: InboxIssueColumn[]): string {
@@ -246,7 +246,7 @@ export function InboxIssueTrailingColumns({
   assigneeName: string | null;
   currentUserId: string | null;
 }) {
-  const activityText = timeAgo(issue.lastExternalCommentAt ?? issue.updatedAt);
+  const activityText = timeAgo(issue.lastActivityAt ?? issue.lastExternalCommentAt ?? issue.updatedAt);
   const userLabel = formatAssigneeUserLabel(issue.assigneeUserId, currentUserId) ?? "User";
 
   return (