feat(#159): add Agent-Level Identity & Attribution

- Add agent_name field to User interface for agent-level tracking
- Extract X-Agent-Name header in getUserFromRequest for attribution
- New GET /api/agents/[id]/attribution endpoint with sections:
  - identity: agent profile, lifetime stats, session info
  - audit: full activity trail + audit log entries for the agent
  - mutations: task changes, comments, status transitions attributed
  - cost: token usage by model with daily trend breakdown
- Backward compatible: X-Agent-Name is optional, existing auth unchanged

Fixes #159

src/app/api/agents/[id]/attribution/route.ts

@@ -0,0 +1,296 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { getDatabase } from '@/lib/db';
+import { requireRole } from '@/lib/auth';
+import { logger } from '@/lib/logger';
+
+/**
+ * GET /api/agents/[id]/attribution - Agent-Level Identity & Attribution
+ *
+ * Returns a comprehensive audit trail and cost attribution report for
+ * a specific agent. Enables per-agent observability, debugging, and
+ * cost analysis in multi-agent environments.
+ *
+ * Query params:
+ *   hours   - Time window (default: 24, max: 720)
+ *   section - Comma-separated: audit,cost,mutations,identity (default: all)
+ *
+ * Response:
+ *   identity   - Agent profile, status, and session info
+ *   audit      - Full audit trail of agent actions
+ *   mutations  - Task/memory/soul changes attributed to this agent
+ *   cost       - Token usage and cost breakdown per model
+ */
+export async function GET(
+  request: NextRequest,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  const auth = requireRole(request, 'viewer');
+  if ('error' in auth) return NextResponse.json({ error: auth.error }, { status: auth.status });
+
+  try {
+    const db = getDatabase();
+    const resolvedParams = await params;
+    const agentId = resolvedParams.id;
+    const workspaceId = auth.user.workspace_id ?? 1;
+
+    // Resolve agent
+    let agent: any;
+    if (/^\d+$/.test(agentId)) {
+      agent = db.prepare('SELECT * FROM agents WHERE id = ? AND workspace_id = ?').get(Number(agentId), workspaceId);
+    } else {
+      agent = db.prepare('SELECT * FROM agents WHERE name = ? AND workspace_id = ?').get(agentId, workspaceId);
+    }
+
+    if (!agent) {
+      return NextResponse.json({ error: 'Agent not found' }, { status: 404 });
+    }
+
+    const { searchParams } = new URL(request.url);
+    const hours = Math.min(Math.max(parseInt(searchParams.get('hours') || '24', 10) || 24, 1), 720);
+    const sectionParam = searchParams.get('section') || 'identity,audit,mutations,cost';
+    const sections = new Set(sectionParam.split(',').map(s => s.trim()));
+
+    const now = Math.floor(Date.now() / 1000);
+    const since = now - hours * 3600;
+
+    const result: Record<string, any> = {
+      agent_name: agent.name,
+      timeframe: { hours, since, until: now },
+    };
+
+    if (sections.has('identity')) {
+      result.identity = buildIdentity(db, agent, workspaceId);
+    }
+
+    if (sections.has('audit')) {
+      result.audit = buildAuditTrail(db, agent.name, workspaceId, since);
+    }
+
+    if (sections.has('mutations')) {
+      result.mutations = buildMutations(db, agent.name, workspaceId, since);
+    }
+
+    if (sections.has('cost')) {
+      result.cost = buildCostAttribution(db, agent.name, workspaceId, since);
+    }
+
+    return NextResponse.json(result);
+  } catch (error) {
+    logger.error({ err: error }, 'GET /api/agents/[id]/attribution error');
+    return NextResponse.json({ error: 'Failed to fetch attribution data' }, { status: 500 });
+  }
+}
+
+/** Agent identity and profile info */
+function buildIdentity(db: any, agent: any, workspaceId: number) {
+  const config = agent.config ? JSON.parse(agent.config) : {};
+
+  // Count total tasks ever assigned
+  const taskStats = db.prepare(`
+    SELECT
+      COUNT(*) as total,
+      SUM(CASE WHEN status = 'done' THEN 1 ELSE 0 END) as completed,
+      SUM(CASE WHEN status IN ('assigned', 'in_progress') THEN 1 ELSE 0 END) as active
+    FROM tasks WHERE assigned_to = ? AND workspace_id = ?
+  `).get(agent.name, workspaceId) as any;
+
+  // Count comments authored
+  const commentCount = (db.prepare(
+    `SELECT COUNT(*) as c FROM comments WHERE author = ? AND workspace_id = ?`
+  ).get(agent.name, workspaceId) as any).c;
+
+  return {
+    id: agent.id,
+    name: agent.name,
+    role: agent.role,
+    status: agent.status,
+    last_seen: agent.last_seen,
+    last_activity: agent.last_activity,
+    created_at: agent.created_at,
+    session_key: agent.session_key ? '***' : null, // Masked for security
+    has_soul: !!agent.soul_content,
+    config_keys: Object.keys(config),
+    lifetime_stats: {
+      tasks_total: taskStats?.total || 0,
+      tasks_completed: taskStats?.completed || 0,
+      tasks_active: taskStats?.active || 0,
+      comments_authored: commentCount,
+    },
+  };
+}
+
+/** Audit trail — all activities attributed to this agent */
+function buildAuditTrail(db: any, agentName: string, workspaceId: number, since: number) {
+  // Activities where this agent is the actor
+  const activities = db.prepare(`
+    SELECT id, type, entity_type, entity_id, description, data, created_at
+    FROM activities
+    WHERE actor = ? AND workspace_id = ? AND created_at >= ?
+    ORDER BY created_at DESC
+    LIMIT 200
+  `).all(agentName, workspaceId, since) as any[];
+
+  // Audit log entries (system-wide, may reference agent)
+  let auditEntries: any[] = [];
+  try {
+    auditEntries = db.prepare(`
+      SELECT id, action, actor, detail, created_at
+      FROM audit_log
+      WHERE (actor = ? OR detail LIKE ?) AND created_at >= ?
+      ORDER BY created_at DESC
+      LIMIT 100
+    `).all(agentName, `%${agentName}%`, since) as any[];
+  } catch {
+    // audit_log table may not exist
+  }
+
+  // Group activities by type for summary
+  const byType: Record<string, number> = {};
+  for (const a of activities) {
+    byType[a.type] = (byType[a.type] || 0) + 1;
+  }
+
+  return {
+    total_activities: activities.length,
+    by_type: byType,
+    activities: activities.map(a => ({
+      ...a,
+      data: a.data ? JSON.parse(a.data) : null,
+    })),
+    audit_log_entries: auditEntries.map(e => ({
+      ...e,
+      detail: e.detail ? JSON.parse(e.detail) : null,
+    })),
+  };
+}
+
+/** Mutations — task changes, comments, status transitions */
+function buildMutations(db: any, agentName: string, workspaceId: number, since: number) {
+  // Task mutations (created, updated, status changes)
+  const taskMutations = db.prepare(`
+    SELECT id, type, entity_type, entity_id, description, data, created_at
+    FROM activities
+    WHERE actor = ? AND workspace_id = ? AND created_at >= ?
+      AND entity_type = 'task'
+      AND type IN ('task_created', 'task_updated', 'task_status_change', 'task_assigned')
+    ORDER BY created_at DESC
+    LIMIT 100
+  `).all(agentName, workspaceId, since) as any[];
+
+  // Comments authored
+  const comments = db.prepare(`
+    SELECT c.id, c.task_id, c.content, c.created_at, c.mentions, t.title as task_title
+    FROM comments c
+    LEFT JOIN tasks t ON c.task_id = t.id AND t.workspace_id = ?
+    WHERE c.author = ? AND c.workspace_id = ? AND c.created_at >= ?
+    ORDER BY c.created_at DESC
+    LIMIT 50
+  `).all(workspaceId, agentName, workspaceId, since) as any[];
+
+  // Agent status changes (by heartbeat or others)
+  const statusChanges = db.prepare(`
+    SELECT id, type, description, data, created_at
+    FROM activities
+    WHERE entity_type = 'agent' AND workspace_id = ?
+      AND created_at >= ?
+      AND (actor = ? OR description LIKE ?)
+    ORDER BY created_at DESC
+    LIMIT 50
+  `).all(workspaceId, since, agentName, `%${agentName}%`) as any[];
+
+  return {
+    task_mutations: taskMutations.map(m => ({
+      ...m,
+      data: m.data ? JSON.parse(m.data) : null,
+    })),
+    comments: comments.map(c => ({
+      ...c,
+      mentions: c.mentions ? JSON.parse(c.mentions) : [],
+      content_preview: c.content?.substring(0, 200) || '',
+    })),
+    status_changes: statusChanges.map(s => ({
+      ...s,
+      data: s.data ? JSON.parse(s.data) : null,
+    })),
+    summary: {
+      task_mutations_count: taskMutations.length,
+      comments_count: comments.length,
+      status_changes_count: statusChanges.length,
+    },
+  };
+}
+
+/** Cost attribution — token usage per model */
+function buildCostAttribution(db: any, agentName: string, workspaceId: number, since: number) {
+  try {
+    const byModel = db.prepare(`
+      SELECT model,
+        COUNT(*) as request_count,
+        SUM(input_tokens) as input_tokens,
+        SUM(output_tokens) as output_tokens
+      FROM token_usage
+      WHERE session_id = ? AND workspace_id = ? AND created_at >= ?
+      GROUP BY model
+      ORDER BY (input_tokens + output_tokens) DESC
+    `).all(agentName, workspaceId, since) as Array<{
+      model: string; request_count: number; input_tokens: number; output_tokens: number
+    }>;
+
+    // Also check session IDs that contain the agent name (e.g. "agentname:cli")
+    const byModelAlt = db.prepare(`
+      SELECT model,
+        COUNT(*) as request_count,
+        SUM(input_tokens) as input_tokens,
+        SUM(output_tokens) as output_tokens
+      FROM token_usage
+      WHERE session_id LIKE ? AND session_id != ? AND workspace_id = ? AND created_at >= ?
+      GROUP BY model
+      ORDER BY (input_tokens + output_tokens) DESC
+    `).all(`${agentName}:%`, agentName, workspaceId, since) as Array<{
+      model: string; request_count: number; input_tokens: number; output_tokens: number
+    }>;
+
+    // Merge results
+    const merged = new Map<string, { model: string; request_count: number; input_tokens: number; output_tokens: number }>();
+    for (const row of [...byModel, ...byModelAlt]) {
+      const existing = merged.get(row.model);
+      if (existing) {
+        existing.request_count += row.request_count;
+        existing.input_tokens += row.input_tokens;
+        existing.output_tokens += row.output_tokens;
+      } else {
+        merged.set(row.model, { ...row });
+      }
+    }
+
+    const models = Array.from(merged.values());
+    const total = models.reduce((acc, r) => ({
+      input_tokens: acc.input_tokens + r.input_tokens,
+      output_tokens: acc.output_tokens + r.output_tokens,
+      requests: acc.requests + r.request_count,
+    }), { input_tokens: 0, output_tokens: 0, requests: 0 });
+
+    // Daily breakdown for trend
+    const daily = db.prepare(`
+      SELECT (created_at / 86400) * 86400 as day_bucket,
+        SUM(input_tokens) as input_tokens,
+        SUM(output_tokens) as output_tokens,
+        COUNT(*) as requests
+      FROM token_usage
+      WHERE (session_id = ? OR session_id LIKE ?) AND workspace_id = ? AND created_at >= ?
+      GROUP BY day_bucket
+      ORDER BY day_bucket ASC
+    `).all(agentName, `${agentName}:%`, workspaceId, since) as any[];
+
+    return {
+      by_model: models,
+      total,
+      daily_trend: daily.map(d => ({
+        date: new Date(d.day_bucket * 1000).toISOString().split('T')[0],
+        ...d,
+      })),
+    };
+  } catch {
+    return { by_model: [], total: { input_tokens: 0, output_tokens: 0, requests: 0 }, daily_trend: [] };
+  }
+}

src/lib/auth.ts

@@ -31,6 +31,8 @@ export interface User {
   created_at: number
   updated_at: number
   last_login_at: number | null
+  /** Agent name when request is made on behalf of a specific agent (via X-Agent-Name header) */
+  agent_name?: string | null
 }
 
 export interface UserSession {
@@ -268,12 +270,15 @@ export function deleteUser(id: number): boolean {
  * For API key auth, returns a synthetic "api" user.
  */
 export function getUserFromRequest(request: Request): User | null {
+  // Extract agent identity header (optional, for attribution)
+  const agentName = (request.headers.get('x-agent-name') || '').trim() || null
+
   // Check session cookie
   const cookieHeader = request.headers.get('cookie') || ''
   const sessionToken = parseCookie(cookieHeader, 'mc-session')
   if (sessionToken) {
     const user = validateSession(sessionToken)
-    if (user) return user
+    if (user) return { ...user, agent_name: agentName }
   }
 
   // Check API key - return synthetic user
@@ -289,6 +294,7 @@ export function getUserFromRequest(request: Request): User | null {
       created_at: 0,
       updated_at: 0,
       last_login_at: null,
+      agent_name: agentName,
     }
   }