feat(activity): unified activity timeline with comment reply support

Replace the comment-only list with a Linear-style unified timeline that
interleaves field changes and comments chronologically.

Backend:
- activity_listeners.go: records field changes (status, assignee, description,
  task completed/failed) to activity_log table on domain events
- Timeline API: GET /api/issues/{id}/timeline merges activity_log + comments
  sorted by created_at
- Comment reply: parent_id column + handler support for threading

Frontend:
- Unified timeline replaces comment list: activity entries as compact muted
  lines, comments as Card components with reply threading
- Filter toggle (All / Comments / Activity)
- Reply UI: inline editor under comments with Cancel/Reply buttons
- Real-time sync for activity:created + comment events
- 10 new Go tests, all passing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/shared/api/client.ts

@@ -30,6 +30,7 @@ import type {
   CreatePersonalAccessTokenResponse,
   RuntimeUsage,
   RuntimePing,
+  TimelineEntry,
 } from "@/shared/types";
 import { type Logger, noopLogger } from "@/shared/logger";
 
@@ -183,13 +184,21 @@ export class ApiClient {
     return this.fetch(`/api/issues/${issueId}/comments`);
   }
 
-  async createComment(issueId: string, content: string, type?: string): Promise<Comment> {
+  async createComment(issueId: string, content: string, type?: string, parentId?: string): Promise<Comment> {
     return this.fetch(`/api/issues/${issueId}/comments`, {
       method: "POST",
-      body: JSON.stringify({ content, type: type ?? "comment" }),
+      body: JSON.stringify({
+        content,
+        type: type ?? "comment",
+        ...(parentId ? { parent_id: parentId } : {}),
+      }),
     });
   }
 
+  async listTimeline(issueId: string): Promise<TimelineEntry[]> {
+    return this.fetch(`/api/issues/${issueId}/timeline`);
+  }
+
   async updateComment(commentId: string, content: string): Promise<Comment> {
     return this.fetch(`/api/comments/${commentId}`, {
       method: "PUT",

apps/web/shared/types/activity.ts

@@ -0,0 +1,15 @@
+export interface TimelineEntry {
+  type: "activity" | "comment";
+  id: string;
+  actor_type: string;
+  actor_id: string;
+  created_at: string;
+  // Activity fields
+  action?: string;
+  details?: Record<string, unknown>;
+  // Comment fields
+  content?: string;
+  parent_id?: string | null;
+  updated_at?: string;
+  comment_type?: string;
+}

apps/web/shared/types/comment.ts

@@ -9,6 +9,7 @@ export interface Comment {
   author_id: string;
   content: string;
   type: CommentType;
+  parent_id: string | null;
   created_at: string;
   updated_at: string;
 }

apps/web/shared/types/events.ts

@@ -2,6 +2,7 @@ import type { Issue } from "./issue";
 import type { Agent } from "./agent";
 import type { InboxItem } from "./inbox";
 import type { Comment } from "./comment";
+import type { TimelineEntry } from "./activity";
 import type { Workspace, MemberWithUser } from "./workspace";
 
 // WebSocket event types (matching Go server protocol/events.go)
@@ -35,7 +36,8 @@ export type WSEventType =
   | "skill:updated"
   | "skill:deleted"
   | "subscriber:added"
-  | "subscriber:removed";
+  | "subscriber:removed"
+  | "activity:created";
 
 export interface WSMessage<T = unknown> {
   type: WSEventType;
@@ -139,3 +141,8 @@ export interface SubscriberRemovedPayload {
   user_type: string;
   user_id: string;
 }
+
+export interface ActivityCreatedPayload {
+  issue_id: string;
+  entry: TimelineEntry;
+}

apps/web/shared/types/index.ts

@@ -24,6 +24,7 @@ export type {
 export type { Workspace, WorkspaceRepo, Member, MemberRole, User, MemberWithUser } from "./workspace";
 export type { InboxItem, InboxSeverity, InboxItemType } from "./inbox";
 export type { Comment, CommentType, CommentAuthorType } from "./comment";
+export type { TimelineEntry } from "./activity";
 export type { IssueSubscriber } from "./subscriber";
 export type { DaemonPairingSession, DaemonPairingSessionStatus, ApproveDaemonPairingSessionRequest } from "./daemon";
 export type * from "./events";