feat(KB-617): add Changes tab to task detail modal with file diffs

- Add modifiedFiles and baseCommitSha fields to task schema for tracking changes
- Capture list of modified files during task execution in the executor
- Add GET /tasks/:id/diff API endpoint to retrieve file list and patches
- Create TaskChangesTab component with expandable file diffs
- Integrate Changes tab into TaskDetailModal for in-progress, in-review, and done tasks
- Add CSS styles for diff viewer with syntax highlighting
- Update API client with fetchTaskDiff function and Project Management types

packages/dashboard/app/api.ts

@@ -1722,3 +1722,160 @@ export async function summarizeTitle(
 
   return data.title;
 }
+
+// ── Project Management API (Multi-Project Support) ───────────────────────
+
+/** Project information returned by project endpoints */
+export interface ProjectInfo {
+  id: string;
+  name: string;
+  path: string;
+  status: "active" | "paused" | "errored" | "initializing";
+  isolationMode: "in-process" | "child-process";
+  createdAt: string;
+  updatedAt: string;
+  lastActivityAt?: string;
+}
+
+/** Project health metrics */
+export interface ProjectHealth {
+  projectId: string;
+  status: "active" | "paused" | "errored" | "initializing";
+  activeTaskCount: number;
+  inFlightAgentCount: number;
+  lastActivityAt?: string;
+  lastErrorAt?: string;
+  lastErrorMessage?: string;
+  totalTasksCompleted: number;
+  totalTasksFailed: number;
+  averageTaskDurationMs?: number;
+  updatedAt: string;
+}
+
+/** Unified activity feed entry */
+export interface ActivityFeedEntry {
+  id: string;
+  timestamp: string;
+  type: "task:created" | "task:moved" | "task:updated" | "task:deleted" | "task:merged" | "task:failed" | "settings:updated";
+  projectId: string;
+  projectName: string;
+  taskId?: string;
+  taskTitle?: string;
+  details: string;
+  metadata?: Record<string, unknown>;
+}
+
+/** Input for creating a new project */
+export interface ProjectCreateInput {
+  name: string;
+  path: string;
+  isolationMode?: "in-process" | "child-process";
+}
+
+/** Options for fetching activity feed */
+export interface FeedOptions {
+  limit?: number;
+  since?: string;
+  projectId?: string;
+  type?: ActivityFeedEntry["type"];
+}
+
+/** Global concurrency state across all projects */
+export interface GlobalConcurrencyState {
+  globalMaxConcurrent: number;
+  currentlyActive: number;
+  queuedCount: number;
+  projectsActive: Record<string, number>;
+}
+
+/** First run status response */
+export interface FirstRunStatus {
+  hasProjects: boolean;
+  singleProjectPath: string | null;
+}
+
+/** Fetch all registered projects */
+export function fetchProjects(): Promise<ProjectInfo[]> {
+  return api<ProjectInfo[]>("/projects");
+}
+
+/** Register a new project */
+export function registerProject(input: ProjectCreateInput): Promise<ProjectInfo> {
+  return api<ProjectInfo>("/projects", {
+    method: "POST",
+    body: JSON.stringify(input),
+  });
+}
+
+/** Unregister a project */
+export function unregisterProject(id: string): Promise<void> {
+  return api<void>(`/projects/${encodeURIComponent(id)}`, {
+    method: "DELETE",
+  });
+}
+
+/** Fetch health metrics for a specific project */
+export function fetchProjectHealth(id: string): Promise<ProjectHealth> {
+  return api<ProjectHealth>(`/projects/${encodeURIComponent(id)}/health`);
+}
+
+/** Fetch unified activity feed */
+export function fetchActivityFeed(options?: FeedOptions): Promise<ActivityFeedEntry[]> {
+  const params = new URLSearchParams();
+  if (options?.limit !== undefined) params.set("limit", String(options.limit));
+  if (options?.since) params.set("since", options.since);
+  if (options?.projectId) params.set("projectId", options.projectId);
+  if (options?.type) params.set("type", options.type);
+  
+  const query = params.size > 0 ? `?${params.toString()}` : "";
+  return api<ActivityFeedEntry[]>(`/activity-feed${query}`);
+}
+
+/** Pause a project */
+export function pauseProject(id: string): Promise<ProjectInfo> {
+  return api<ProjectInfo>(`/projects/${encodeURIComponent(id)}/pause`, {
+    method: "POST",
+  });
+}
+
+/** Resume a paused project */
+export function resumeProject(id: string): Promise<ProjectInfo> {
+  return api<ProjectInfo>(`/projects/${encodeURIComponent(id)}/resume`, {
+    method: "POST",
+  });
+}
+
+/** Fetch first run status to detect if user needs setup wizard */
+export function fetchFirstRunStatus(): Promise<FirstRunStatus> {
+  return api<FirstRunStatus>("/first-run-status");
+}
+
+/** Fetch global concurrency state */
+export function fetchGlobalConcurrency(): Promise<GlobalConcurrencyState> {
+  return api<GlobalConcurrencyState>("/global-concurrency");
+}
+
+/** Fetch tasks for a specific project */
+export function fetchProjectTasks(projectId: string, limit?: number, offset?: number): Promise<Task[]> {
+  const params = new URLSearchParams();
+  params.set("projectId", projectId);
+  if (limit !== undefined) params.set("limit", String(limit));
+  if (offset !== undefined) params.set("offset", String(offset));
+  return api<Task[]>(`/tasks?${params.toString()}`);
+}
+
+/** Fetch project-specific config */
+export function fetchProjectConfig(projectId: string): Promise<{ maxConcurrent: number; rootDir: string }> {
+  return api<{ maxConcurrent: number; rootDir: string }>(`/projects/${encodeURIComponent(projectId)}/config`);
+}
+
+/** Diff information for a task */
+export interface TaskDiff {
+  files: string[];
+  diffs: Record<string, { stat: string; patch: string }>;
+}
+
+/** Fetch diff information for a task */
+export function fetchTaskDiff(taskId: string): Promise<TaskDiff> {
+  return api<TaskDiff>(`/tasks/${encodeURIComponent(taskId)}/diff`);
+}

packages/dashboard/app/components/TaskDetailModal.tsx

@@ -13,6 +13,7 @@ import { ModelSelectorTab } from "./ModelSelectorTab";
 import { PrSection } from "./PrSection";
 import { TaskComments } from "./TaskComments";
 import { MergeDetails } from "./MergeDetails";
+import { TaskChangesTab } from "./TaskChangesTab";
 
 interface ModelSelection {
   provider?: string;
@@ -105,7 +106,7 @@ export function TaskDetailModal({
   addToast,
   githubTokenConfigured,
 }: TaskDetailModalProps) {
-  const [activeTab, setActiveTab] = useState<"definition" | "activity" | "agent-log" | "steering" | "comments" | "model">("definition");
+  const [activeTab, setActiveTab] = useState<"definition" | "activity" | "agent-log" | "changes" | "steering" | "comments" | "model">("definition");
   const [attachments, setAttachments] = useState<TaskAttachment[]>(task.attachments || []);
   const [uploading, setUploading] = useState(false);
   const [dependencies, setDependencies] = useState<string[]>(task.dependencies || []);
@@ -671,6 +672,14 @@ export function TaskDetailModal({
             >
               Agent Log
             </button>
+            {(task.column === "in-progress" || task.column === "in-review" || task.column === "done") && (
+              <button
+                className={`detail-tab${activeTab === "changes" ? " detail-tab-active" : ""}`}
+                onClick={() => setActiveTab("changes")}
+              >
+                Changes
+              </button>
+            )}
             <button
               className={`detail-tab${activeTab === "steering" ? " detail-tab-active" : ""}`}
               onClick={() => setActiveTab("steering")}
@@ -703,6 +712,8 @@ export function TaskDetailModal({
                 validatorModel={getValidatorSelection(task)}
               />
             </div>
+          ) : activeTab === "changes" ? (
+            <TaskChangesTab taskId={task.id} worktree={task.worktree} />
           ) : activeTab === "steering" ? (
             <SteeringTab task={task} addToast={addToast} />
           ) : activeTab === "comments" ? (

packages/dashboard/app/styles.css

@@ -11054,3 +11054,134 @@ html .column.drag-over * {
 [data-theme="light"] .gm-load-more:hover {
   background: rgba(0, 0, 0, 0.03);
 }
+
+/* ── Task Changes Tab Styles ─────────────────────────────────────────────── */
+
+.task-changes-tab {
+  padding: 16px;
+}
+
+.changes-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  margin-bottom: 16px;
+}
+
+.changes-header h4 {
+  margin: 0;
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  font-size: 14px;
+  font-weight: 500;
+}
+
+.changes-file-list {
+  border: 1px solid var(--border, #30363d);
+  border-radius: 8px;
+  overflow: hidden;
+}
+
+.changes-file-item {
+  border-bottom: 1px solid var(--border, #30363d);
+}
+
+.changes-file-item:last-child {
+  border-bottom: none;
+}
+
+.changes-file-item.expanded {
+  background: var(--bg-secondary, #161b22);
+}
+
+.changes-file-header {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 10px 12px;
+  background: none;
+  border: none;
+  width: 100%;
+  text-align: left;
+  cursor: pointer;
+  color: var(--text-primary, #c9d1d9);
+  font-size: 13px;
+  transition: background 0.15s;
+}
+
+.changes-file-header:hover {
+  background: var(--bg-hover, #1f242c);
+}
+
+.changes-file-toggle {
+  display: flex;
+  align-items: center;
+  color: var(--text-secondary, #8b949e);
+  flex-shrink: 0;
+}
+
+.changes-file-status {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 20px;
+  height: 20px;
+  border-radius: 4px;
+  font-size: 11px;
+  font-weight: 600;
+  flex-shrink: 0;
+}
+
+.changes-file-path {
+  flex: 1;
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
+}
+
+.changes-file-stat {
+  color: var(--text-secondary, #8b949e);
+  font-size: 11px;
+  flex-shrink: 0;
+  margin-left: 8px;
+}
+
+.changes-file-content {
+  border-top: 1px solid var(--border, #30363d);
+  background: var(--bg-primary, #0d1117);
+}
+
+.changes-diff-patch {
+  margin: 0;
+  padding: 12px;
+  font-size: 12px;
+  line-height: 1.5;
+  overflow-x: auto;
+  white-space: pre;
+  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
+  color: var(--text-primary, #c9d1d9);
+}
+
+.changes-diff-patch code {
+  background: none;
+  padding: 0;
+}
+
+/* Syntax highlighting for diff */
+.changes-diff-patch .diff-add,
+.changes-diff-patch [data-prefix="+"] {
+  color: #3fb950;
+}
+
+.changes-diff-patch .diff-del,
+.changes-diff-patch [data-prefix="-"] {
+  color: #f85149;
+}
+
+.changes-diff-patch .diff-hunk,
+.changes-diff-patch [data-prefix="@@"] {
+  color: #58a6ff;
+}