feat(sessions): progress bb-buff.3.3 - Active Mission Pathing (data layer)

STORY:
The Sessions Hub needs to show which task each agent is working on,
creating a visual "mission link" between agents and their active work.

COLLABORATION:
We implemented the data layer for mission pathing:
- getAgentActiveMissions() returns tasks owned by an agent
- getActiveMissionCount() for badge indicators
- getMissionsByAgent() groups all missions for batch rendering

DELIVERABLES:
- src/lib/agent-sessions.ts extended with mission functions
- Tests: 8/8 PASS in tests/lib/mission-pathing.test.ts

STATUS: in_progress (visual rendering layer still pending)
Visual path lines would require SVG overlay + position tracking.

CLOSES: partial bb-buff.3.3

tests/lib/mission-pathing.test.ts

@@ -0,0 +1,148 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { 
+  getAgentActiveMissions, 
+  getActiveMissionCount,
+  getMissionsByAgent,
+  type SessionTaskCard, 
+  type EpicBucket 
+} from '../../src/lib/agent-sessions';
+
+/**
+ * Tests for bb-buff.3.3: Active Mission Pathing
+ * 
+ * These tests verify the mapping between working agents and their tasks.
+ */
+
+// Helper to create test data
+function makeBucket(tasks: Partial<SessionTaskCard>[]): EpicBucket {
+  return {
+    epic: { id: 'epic-1', title: 'Test Epic', status: 'open' },
+    tasks: tasks.map((t, i) => ({
+      id: t.id || `task-${i}`,
+      title: t.title || 'Test Task',
+      epicId: 'epic-1',
+      status: t.status || 'in_progress',
+      sessionState: t.sessionState || 'active',
+      owner: t.owner || null,
+      lastActor: null,
+      lastActivityAt: new Date().toISOString(),
+      communication: { unreadCount: 0, pendingRequired: false, latestSnippet: null },
+      ...t
+    })) as SessionTaskCard[]
+  };
+}
+
+test('getAgentActiveMissions returns tasks owned by agent', () => {
+  const feed = [
+    makeBucket([
+      { id: 'task-1', owner: 'agent-alpha' },
+      { id: 'task-2', owner: 'agent-beta' },
+      { id: 'task-3', owner: 'agent-alpha' },
+    ])
+  ];
+  
+  const missions = getAgentActiveMissions(feed, 'agent-alpha');
+  assert.equal(missions.length, 2);
+  assert.equal(missions[0].id, 'task-1');
+  assert.equal(missions[1].id, 'task-3');
+});
+
+test('getAgentActiveMissions excludes closed tasks', () => {
+  const feed = [
+    makeBucket([
+      { id: 'task-1', owner: 'agent-alpha', status: 'in_progress' },
+      { id: 'task-2', owner: 'agent-alpha', status: 'closed' },
+    ])
+  ];
+  
+  const missions = getAgentActiveMissions(feed, 'agent-alpha');
+  assert.equal(missions.length, 1);
+  assert.equal(missions[0].id, 'task-1');
+});
+
+test('getAgentActiveMissions returns empty array for unknown agent', () => {
+  const feed = [
+    makeBucket([
+      { id: 'task-1', owner: 'agent-alpha' },
+    ])
+  ];
+  
+  const missions = getAgentActiveMissions(feed, 'unknown-agent');
+  assert.equal(missions.length, 0);
+});
+
+test('getAgentActiveMissions returns empty array for null owner', () => {
+  const feed = [
+    makeBucket([
+      { id: 'task-1', owner: null },
+    ])
+  ];
+  
+  const missions = getAgentActiveMissions(feed, 'agent-alpha');
+  assert.equal(missions.length, 0);
+});
+
+test('getAgentActiveMissions works across multiple epics', () => {
+  const bucket1 = makeBucket([{ id: 'task-1', owner: 'agent-alpha', epicId: 'epic-1' }]);
+  const bucket2: EpicBucket = {
+    epic: { id: 'epic-2', title: 'Epic 2', status: 'open' },
+    tasks: [{
+      id: 'task-2',
+      title: 'Task in Epic 2',
+      epicId: 'epic-2',
+      status: 'in_progress',
+      sessionState: 'active',
+      owner: 'agent-alpha',
+      lastActor: null,
+      lastActivityAt: new Date().toISOString(),
+      communication: { unreadCount: 0, pendingRequired: false, latestSnippet: null },
+    }]
+  };
+  
+  const missions = getAgentActiveMissions([bucket1, bucket2], 'agent-alpha');
+  assert.equal(missions.length, 2);
+});
+
+test('getActiveMissionCount returns correct count', () => {
+  const feed = [
+    makeBucket([
+      { id: 'task-1', owner: 'agent-alpha' },
+      { id: 'task-2', owner: 'agent-alpha' },
+      { id: 'task-3', owner: 'agent-beta' },
+    ])
+  ];
+  
+  assert.equal(getActiveMissionCount(feed, 'agent-alpha'), 2);
+  assert.equal(getActiveMissionCount(feed, 'agent-beta'), 1);
+  assert.equal(getActiveMissionCount(feed, 'unknown'), 0);
+});
+
+test('getMissionsByAgent groups all agents', () => {
+  const feed = [
+    makeBucket([
+      { id: 'task-1', owner: 'agent-alpha' },
+      { id: 'task-2', owner: 'agent-beta' },
+      { id: 'task-3', owner: 'agent-alpha' },
+      { id: 'task-4', owner: null }, // No owner
+    ])
+  ];
+  
+  const byAgent = getMissionsByAgent(feed);
+  assert.deepEqual(Object.keys(byAgent).sort(), ['agent-alpha', 'agent-beta']);
+  assert.equal(byAgent['agent-alpha'].length, 2);
+  assert.equal(byAgent['agent-beta'].length, 1);
+});
+
+test('getMissionsByAgent excludes closed tasks', () => {
+  const feed = [
+    makeBucket([
+      { id: 'task-1', owner: 'agent-alpha', status: 'in_progress' },
+      { id: 'task-2', owner: 'agent-alpha', status: 'closed' },
+    ])
+  ];
+  
+  const byAgent = getMissionsByAgent(feed);
+  assert.equal(byAgent['agent-alpha'].length, 1);
+  assert.equal(byAgent['agent-alpha'][0].id, 'task-1');
+});