Add comprehensive Agent Mail coordination tests (bd-pdjb)

- Created test_multi_agent_coordination.py with 4 fast tests (<11s total)
- Tests cover fairness (10 agents, 5 issues), notifications, handoff, idempotency
- Documented complete test coverage in AGENT_MAIL_TEST_COVERAGE.md
- 66 total tests across 5 files validating multi-agent reliability
- Closed bd-pdjb (Testing & Validation epic)

tests/integration/AGENT_MAIL_TEST_COVERAGE.md

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+# Agent Mail Integration Test Coverage
+
+## Test Suite Summary
+
+**Total test time**: ~55 seconds (all suites)
+**Total tests**: 66 tests across 5 files
+
+## Coverage by Category
+
+### 1. HTTP Adapter Unit Tests (`lib/test_beads_mail_adapter.py`)
+**51 tests in 0.019s**
+
+✅ **Enabled/Disabled Mode**
+- Server available vs unavailable
+- Graceful degradation when server dies mid-operation
+- Operations no-op when disabled
+
+✅ **Reservation Operations**
+- Successful reservation (201)
+- Conflict handling (409)
+- Custom TTL support
+- Multiple reservations by same agent
+- Release operations (204)
+- Double release idempotency
+
+✅ **HTTP Error Handling**
+- 500 Internal Server Error
+- 404 Not Found
+- 409 Conflict with malformed body
+- Network timeouts
+- Malformed JSON responses
+- Empty response bodies (204 No Content)
+
+✅ **Configuration**
+- Environment variable configuration
+- Constructor parameter overrides
+- URL normalization (trailing slash removal)
+- Default agent name from hostname
+- Timeout configuration
+
+✅ **Authorization**
+- Bearer token headers
+- Missing token behavior
+- Content-Type headers
+
+✅ **Request Validation**
+- Body structure for reservations
+- Body structure for notifications
+- URL structure for releases
+- URL structure for inbox checks
+
+✅ **Inbox & Notifications**
+- Send notifications
+- Check inbox with messages
+- Empty inbox handling
+- Dict wrapper responses
+- Large message lists (100 messages)
+- Nested payload data
+- Empty and large payloads
+- Unicode handling
+
+### 2. Multi-Agent Race Conditions (`tests/integration/test_agent_race.py`)
+**3 tests in ~15s**
+
+✅ **Collision Prevention**
+- 3 agents competing for 1 issue (WITH Agent Mail)
+- Only one winner with reservations
+- Multiple agents without Agent Mail (collision demo)
+
+✅ **Stress Testing**
+- 10 agents competing for 1 issue
+- Exactly one winner guaranteed
+- JSONL consistency verification
+
+### 3. Server Failure Scenarios (`tests/integration/test_mail_failures.py`)
+**7 tests in ~20s**
+
+✅ **Failure Modes**
+- Server never started (connection refused)
+- Server crash during operation
+- Network partition (timeout)
+- Server 500 errors
+- Invalid bearer token (401)
+- Malformed JSON responses
+
+✅ **Graceful Degradation**
+- Agents continue working in Beads-only mode
+- JSONL remains consistent across failures
+- No crashes or data loss
+
+### 4. Reservation TTL & Expiration (`tests/integration/test_reservation_ttl.py`)
+**4 tests in ~60s** (includes 30s waits for expiration)
+
+✅ **Time-Based Behavior**
+- Short TTL reservations (30s)
+- Reservation blocking verification
+- Auto-release after expiration
+- Renewal/heartbeat mechanisms
+
+### 5. Multi-Agent Coordination (`tests/integration/test_multi_agent_coordination.py`)
+**4 tests in ~11s** ⭐ NEW
+
+✅ **Fairness**
+- 10 agents competing for 5 issues
+- Each issue claimed exactly once
+- No duplicate claims in JSONL
+
+✅ **Notifications**
+- End-to-end message delivery
+- Inbox consumption (messages cleared after read)
+- Message structure validation
+
+✅ **Handoff Scenarios**
+- Agent releases, another immediately claims
+- Clean reservation ownership transfer
+
+✅ **Idempotency**
+- Double reserve by same agent (safe)
+- Double release by same agent (safe)
+- Reservation count verification
+
+## Coverage Gaps (Intentionally Not Tested)
+
+### Low-Priority Edge Cases
+- **Path traversal in issue IDs**: Issue IDs are validated elsewhere in bd
+- **429 Retry-After logic**: Nice-to-have, not critical for v1
+- **HTTPS/TLS verification**: Out of scope for integration layer
+- **Re-enable after recovery**: Complex, requires persistent health checking
+- **Token rotation mid-run**: Rare scenario, not worth complexity
+- **Slow tests**: 50+ agent stress tests, soak tests, inbox flood (>10k messages)
+
+### Why Skipped
+These scenarios are either:
+1. **Validated elsewhere** (e.g., issue ID validation in bd core)
+2. **Low probability** (e.g., token rotation during agent run)
+3. **Nice-to-have features** (e.g., automatic re-enable, retry policies)
+4. **Too slow for CI** (e.g., multi-hour soak tests, 50-agent races)
+
+## Test Execution
+
+### Run All Tests
+```bash
+# Unit tests (fast, 0.02s)
+python3 lib/test_beads_mail_adapter.py
+
+# Multi-agent coordination (11s)
+python3 tests/integration/test_multi_agent_coordination.py
+
+# Race conditions (15s, requires Agent Mail server or falls back)
+python3 tests/integration/test_agent_race.py
+
+# Failure scenarios (20s)
+python3 tests/integration/test_mail_failures.py
+
+# TTL/expiration (60s - includes deliberate waits)
+python3 tests/integration/test_reservation_ttl.py
+```
+
+### Quick Validation (No Slow Tests)
+```bash
+python3 lib/test_beads_mail_adapter.py
+python3 tests/integration/test_multi_agent_coordination.py
+python3 tests/integration/test_mail_failures.py
+# Total: ~31s
+```
+
+## Assertions Verified
+
+✅ **Correctness**
+- Only one agent claims each issue (collision prevention)
+- Notifications deliver correctly
+- Reservations block other agents
+- JSONL remains consistent across all failure modes
+
+✅ **Reliability**
+- Graceful degradation when server unavailable
+- Idempotent operations don't corrupt state
+- Expired reservations auto-release
+- Handoffs work cleanly
+
+✅ **Performance**
+- Fast timeout detection (1-2s)
+- No blocking on server failures
+- Tests complete in reasonable time (<2min total)
+
+## Future Enhancements (Optional)
+
+If real-world usage reveals issues:
+
+1. **Retry policies** with exponential backoff for 429/5xx
+2. **Pagination** for inbox/reservations (if >1k messages)
+3. **Automatic re-enable** with periodic health checks
+4. **Agent instance IDs** to prevent same-name collisions
+5. **Soak/stress testing** for production validation
+
+Current test suite provides **strong confidence** for multi-agent workflows without overengineering.

tests/integration/test_multi_agent_coordination.py

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+#!/usr/bin/env python3
+"""
+Multi-Agent Coordination Test Suite
+
+Fast tests (<30s total) covering critical multi-agent scenarios:
+- Fairness: N agents claiming M issues
+- Notifications: End-to-end message passing
+- Handoff: Release → immediate claim by another agent
+- Idempotency: Double operations by same agent
+"""
+
+import json
+import subprocess
+import tempfile
+import shutil
+import sys
+import time
+from pathlib import Path
+from multiprocessing import Process, Queue
+from threading import Thread, Lock
+from http.server import HTTPServer, BaseHTTPRequestHandler
+import socket
+
+# Add lib directory for beads_mail_adapter
+lib_path = Path(__file__).parent.parent.parent / "lib"
+sys.path.insert(0, str(lib_path))
+
+from beads_mail_adapter import AgentMailAdapter
+
+
+class MockAgentMailServer:
+    """Lightweight mock server with reservations and notifications."""
+    
+    def __init__(self, port: int = 0):
+        self.port = port
+        self.server = None
+        self.thread = None
+        self.reservations = {}  # file_path -> agent_name
+        self.notifications = {}  # agent_name -> [messages]
+        self.lock = Lock()
+        
+    def start(self) -> int:
+        """Start server and return port."""
+        handler = self._create_handler()
+        
+        if self.port == 0:
+            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+                s.bind(('', 0))
+                s.listen(1)
+                self.port = s.getsockname()[1]
+        
+        self.server = HTTPServer(('127.0.0.1', self.port), handler)
+        self.thread = Thread(target=self.server.serve_forever, daemon=True)
+        self.thread.start()
+        time.sleep(0.1)
+        return self.port
+    
+    def stop(self):
+        if self.server:
+            self.server.shutdown()
+            self.server.server_close()
+    
+    def _create_handler(self):
+        parent = self
+        
+        class Handler(BaseHTTPRequestHandler):
+            def log_message(self, *args):
+                pass
+            
+            def do_GET(self):
+                if self.path == "/api/health":
+                    self.send_response(200)
+                    self.send_header('Content-Type', 'application/json')
+                    self.end_headers()
+                    self.wfile.write(b'{"status": "ok"}')
+                
+                # Get inbox: /api/notifications/{agent_name}
+                elif self.path.startswith("/api/notifications/"):
+                    agent_name = self.path.split('/')[-1]
+                    with parent.lock:
+                        messages = parent.notifications.get(agent_name, [])
+                        parent.notifications[agent_name] = []  # Clear after read
+                    
+                    self.send_response(200)
+                    self.send_header('Content-Type', 'application/json')
+                    self.end_headers()
+                    self.wfile.write(json.dumps(messages).encode())
+                
+                elif self.path == "/api/reservations":
+                    with parent.lock:
+                        res_list = [
+                            {"file_path": fp, "agent_name": agent}
+                            for fp, agent in parent.reservations.items()
+                        ]
+                    
+                    self.send_response(200)
+                    self.send_header('Content-Type', 'application/json')
+                    self.end_headers()
+                    self.wfile.write(json.dumps(res_list).encode())
+                
+                else:
+                    self.send_response(404)
+                    self.end_headers()
+            
+            def do_POST(self):
+                content_length = int(self.headers.get('Content-Length', 0))
+                body = self.rfile.read(content_length) if content_length > 0 else b'{}'
+                data = json.loads(body.decode('utf-8'))
+                
+                # Reserve: /api/reservations
+                if self.path == "/api/reservations":
+                    file_path = data.get("file_path")
+                    agent_name = data.get("agent_name")
+                    
+                    with parent.lock:
+                        if file_path in parent.reservations:
+                            existing = parent.reservations[file_path]
+                            if existing != agent_name:
+                                # Conflict
+                                self.send_response(409)
+                                self.send_header('Content-Type', 'application/json')
+                                self.end_headers()
+                                self.wfile.write(json.dumps({
+                                    "error": f"Already reserved by {existing}"
+                                }).encode())
+                                return
+                            # else: same agent re-reserving (idempotent)
+                        
+                        parent.reservations[file_path] = agent_name
+                    
+                    self.send_response(201)
+                    self.send_header('Content-Type', 'application/json')
+                    self.end_headers()
+                    self.wfile.write(b'{"status": "reserved"}')
+                
+                # Notify: /api/notifications
+                elif self.path == "/api/notifications":
+                    from_agent = data.get("from_agent")
+                    event_type = data.get("event_type")
+                    payload = data.get("payload", {})
+                    
+                    # Broadcast to all OTHER agents
+                    with parent.lock:
+                        for agent_name in list(parent.notifications.keys()):
+                            if agent_name != from_agent:
+                                parent.notifications[agent_name].append({
+                                    "from": from_agent,
+                                    "event": event_type,
+                                    "data": payload
+                                })
+                        
+                        # If target agent specified, ensure they get it
+                        to_agent = payload.get("to_agent")
+                        if to_agent and to_agent not in parent.notifications:
+                            parent.notifications[to_agent] = [{
+                                "from": from_agent,
+                                "event": event_type,
+                                "data": payload
+                            }]
+                    
+                    self.send_response(201)
+                    self.send_header('Content-Type', 'application/json')
+                    self.end_headers()
+                    self.wfile.write(b'{"status": "sent"}')
+                
+                else:
+                    self.send_response(404)
+                    self.end_headers()
+            
+            def do_DELETE(self):
+                # Release: /api/reservations/{agent}/{issue_id}
+                parts = self.path.split('/')
+                if len(parts) >= 5:
+                    agent_name = parts[3]
+                    issue_id = parts[4]
+                    file_path = f".beads/issues/{issue_id}"
+                    
+                    with parent.lock:
+                        if file_path in parent.reservations:
+                            if parent.reservations[file_path] == agent_name:
+                                del parent.reservations[file_path]
+                    
+                    self.send_response(204)
+                    self.end_headers()
+                else:
+                    self.send_response(404)
+                    self.end_headers()
+        
+        return Handler
+
+
+class TestAgent:
+    """Minimal test agent."""
+    
+    def __init__(self, workspace: str, agent_name: str, mail_url: str):
+        self.workspace = workspace
+        self.agent_name = agent_name
+        self.mail = AgentMailAdapter(url=mail_url, agent_name=agent_name, timeout=2)
+    
+    def run_bd(self, *args):
+        cmd = ["bd", "--no-daemon"] + list(args) + ["--json"]
+        result = subprocess.run(cmd, cwd=self.workspace, capture_output=True, text=True)
+        if result.returncode != 0:
+            return {"error": result.stderr}
+        if result.stdout.strip():
+            try:
+                return json.loads(result.stdout)
+            except:
+                return {"error": "Invalid JSON"}
+        return {}
+    
+    def create_issue(self, title: str) -> str:
+        result = self.run_bd("create", title, "-p", "1")
+        return result.get("id")
+    
+    def claim_issue(self, issue_id: str) -> bool:
+        if self.mail.enabled and not self.mail.reserve_issue(issue_id):
+            return False
+        result = self.run_bd("update", issue_id, "--status", "in_progress")
+        return "error" not in result
+    
+    def release_issue(self, issue_id: str):
+        if self.mail.enabled:
+            self.mail.release_issue(issue_id)
+
+
+def agent_claim_worker(agent_name: str, workspace: str, issue_id: str, 
+                       mail_url: str, result_queue: Queue):
+    """Worker that tries to claim a single issue."""
+    try:
+        agent = TestAgent(workspace, agent_name, mail_url)
+        success = agent.claim_issue(issue_id)
+        result_queue.put({"agent": agent_name, "issue": issue_id, "success": success})
+    except Exception as e:
+        result_queue.put({"agent": agent_name, "issue": issue_id, "success": False, "error": str(e)})
+
+
+def test_fairness_n_agents_m_issues():
+    """Test that N agents competing for M issues results in exactly M claims."""
+    print("\n" + "="*70)
+    print("TEST 1: Fairness - 10 agents, 5 issues")
+    print("="*70)
+    
+    workspace = tempfile.mkdtemp(prefix="bd-test-fairness-")
+    server = MockAgentMailServer()
+    
+    try:
+        subprocess.run(["bd", "init", "--quiet", "--prefix", "test"], 
+                      cwd=workspace, check=True, capture_output=True)
+        
+        port = server.start()
+        mail_url = f"http://127.0.0.1:{port}"
+        
+        # Create 5 issues
+        agent = TestAgent(workspace, "setup", mail_url)
+        issues = [agent.create_issue(f"Issue {i+1}") for i in range(5)]
+        
+        # Spawn 10 agents trying to claim all 5 issues
+        result_queue = Queue()
+        processes = []
+        
+        for agent_num in range(10):
+            for issue_id in issues:
+                p = Process(target=agent_claim_worker, 
+                          args=(f"agent-{agent_num}", workspace, issue_id, mail_url, result_queue))
+                processes.append(p)
+        
+        # Start all at once
+        for p in processes:
+            p.start()
+        
+        for p in processes:
+            p.join(timeout=10)
+        
+        # Collect results
+        results = []
+        while not result_queue.empty():
+            results.append(result_queue.get())
+        
+        # Count successful claims per issue
+        claims_per_issue = {}
+        for r in results:
+            if r["success"]:
+                issue = r["issue"]
+                claims_per_issue[issue] = claims_per_issue.get(issue, 0) + 1
+        
+        print(f"   • Total attempts: {len(results)}")
+        print(f"   • Successful claims: {sum(claims_per_issue.values())}")
+        print(f"   • Claims per issue: {claims_per_issue}")
+        
+        # Verify exactly 1 claim per issue
+        for issue_id in issues:
+            claims = claims_per_issue.get(issue_id, 0)
+            assert claims == 1, f"Issue {issue_id} claimed {claims} times (expected 1)"
+        
+        print("✅ PASS: Each issue claimed exactly once")
+        return True
+        
+    finally:
+        server.stop()
+        shutil.rmtree(workspace, ignore_errors=True)
+
+
+def test_notification_end_to_end():
+    """Test notifications from agent1 to agent2."""
+    print("\n" + "="*70)
+    print("TEST 2: Notification End-to-End")
+    print("="*70)
+    
+    workspace = tempfile.mkdtemp(prefix="bd-test-notify-")
+    server = MockAgentMailServer()
+    
+    try:
+        subprocess.run(["bd", "init", "--quiet", "--prefix", "test"], 
+                      cwd=workspace, check=True, capture_output=True)
+        
+        port = server.start()
+        mail_url = f"http://127.0.0.1:{port}"
+        
+        # Create two agents
+        agent1 = TestAgent(workspace, "agent1", mail_url)
+        agent2 = TestAgent(workspace, "agent2", mail_url)
+        
+        # Register agent2's inbox
+        server.notifications["agent2"] = []
+        
+        # Agent1 sends notification
+        sent = agent1.mail.notify("task_completed", {
+            "issue_id": "bd-123",
+            "status": "done",
+            "to_agent": "agent2"
+        })
+        
+        assert sent, "Should send notification"
+        
+        # Agent2 checks inbox
+        messages = agent2.mail.check_inbox()
+        
+        print(f"   • Agent1 sent notification")
+        print(f"   • Agent2 received {len(messages)} message(s)")
+        
+        assert len(messages) == 1, f"Expected 1 message, got {len(messages)}"
+        assert messages[0]["from"] == "agent1"
+        assert messages[0]["event"] == "task_completed"
+        assert messages[0]["data"]["issue_id"] == "bd-123"
+        
+        # Second check should be empty (messages consumed)
+        messages2 = agent2.mail.check_inbox()
+        assert len(messages2) == 0, "Inbox should be empty after read"
+        
+        print("✅ PASS: Notification delivered correctly")
+        return True
+        
+    finally:
+        server.stop()
+        shutil.rmtree(workspace, ignore_errors=True)
+
+
+def test_reservation_handoff():
+    """Test immediate claim after release (handoff scenario)."""
+    print("\n" + "="*70)
+    print("TEST 3: Reservation Handoff")
+    print("="*70)
+    
+    workspace = tempfile.mkdtemp(prefix="bd-test-handoff-")
+    server = MockAgentMailServer()
+    
+    try:
+        subprocess.run(["bd", "init", "--quiet", "--prefix", "test"], 
+                      cwd=workspace, check=True, capture_output=True)
+        
+        port = server.start()
+        mail_url = f"http://127.0.0.1:{port}"
+        
+        agent1 = TestAgent(workspace, "agent1", mail_url)
+        agent2 = TestAgent(workspace, "agent2", mail_url)
+        
+        # Agent1 creates and claims issue
+        issue_id = agent1.create_issue("Handoff test")
+        claimed1 = agent1.claim_issue(issue_id)
+        assert claimed1, "Agent1 should claim issue"
+        
+        # Agent2 tries to claim (should fail - reserved)
+        claimed2_before = agent2.claim_issue(issue_id)
+        assert not claimed2_before, "Agent2 should be blocked"
+        
+        # Agent1 releases
+        agent1.release_issue(issue_id)
+        
+        # Agent2 immediately claims (handoff)
+        claimed2_after = agent2.claim_issue(issue_id)
+        assert claimed2_after, "Agent2 should claim after release"
+        
+        # Verify reservation ownership
+        reservations = agent2.mail.get_reservations()
+        assert len(reservations) == 1
+        assert reservations[0]["agent_name"] == "agent2"
+        
+        print("✅ PASS: Clean handoff from agent1 to agent2")
+        return True
+        
+    finally:
+        server.stop()
+        shutil.rmtree(workspace, ignore_errors=True)
+
+
+def test_idempotent_operations():
+    """Test double reserve and double release by same agent."""
+    print("\n" + "="*70)
+    print("TEST 4: Idempotent Operations")
+    print("="*70)
+    
+    workspace = tempfile.mkdtemp(prefix="bd-test-idem-")
+    server = MockAgentMailServer()
+    
+    try:
+        subprocess.run(["bd", "init", "--quiet", "--prefix", "test"], 
+                      cwd=workspace, check=True, capture_output=True)
+        
+        port = server.start()
+        mail_url = f"http://127.0.0.1:{port}"
+        
+        agent = TestAgent(workspace, "agent1", mail_url)
+        issue_id = agent.create_issue("Idempotency test")
+        
+        # Reserve twice (idempotent)
+        reserve1 = agent.mail.reserve_issue(issue_id)
+        reserve2 = agent.mail.reserve_issue(issue_id)
+        
+        assert reserve1, "First reserve should succeed"
+        assert reserve2, "Second reserve should be idempotent (same agent)"
+        
+        # Verify only one reservation
+        reservations = agent.mail.get_reservations()
+        assert len(reservations) == 1, f"Should have 1 reservation, got {len(reservations)}"
+        
+        # Release twice (idempotent)
+        release1 = agent.mail.release_issue(issue_id)
+        release2 = agent.mail.release_issue(issue_id)
+        
+        assert release1, "First release should succeed"
+        assert release2, "Second release should be idempotent (no error)"
+        
+        # Verify no reservations
+        reservations_after = agent.mail.get_reservations()
+        assert len(reservations_after) == 0, "Should have 0 reservations after release"
+        
+        print("✅ PASS: Double reserve and release are idempotent")
+        return True
+        
+    finally:
+        server.stop()
+        shutil.rmtree(workspace, ignore_errors=True)
+
+
+def main():
+    """Run coordination tests."""
+    print("🧪 Multi-Agent Coordination Test Suite")
+    print("Fast tests for critical coordination scenarios")
+    
+    try:
+        subprocess.run(["bd", "--version"], capture_output=True, check=True)
+    except (subprocess.CalledProcessError, FileNotFoundError):
+        print("❌ ERROR: bd command not found")
+        sys.exit(1)
+    
+    tests = [
+        ("Fairness (10 agents, 5 issues)", test_fairness_n_agents_m_issues),
+        ("Notification end-to-end", test_notification_end_to_end),
+        ("Reservation handoff", test_reservation_handoff),
+        ("Idempotent operations", test_idempotent_operations),
+    ]
+    
+    passed = 0
+    failed = 0
+    start_time = time.time()
+    
+    for name, test_func in tests:
+        try:
+            if test_func():
+                passed += 1
+        except AssertionError as e:
+            print(f"\n❌ FAIL: {name}")
+            print(f"   {e}")
+            failed += 1
+        except Exception as e:
+            print(f"\n💥 ERROR in {name}: {e}")
+            import traceback
+            traceback.print_exc()
+            failed += 1
+    
+    elapsed = time.time() - start_time
+    
+    print("\n" + "="*70)
+    print("SUMMARY")
+    print("="*70)
+    print(f"✅ Passed: {passed}/{len(tests)}")
+    print(f"❌ Failed: {failed}/{len(tests)}")
+    print(f"⏱️  Total time: {elapsed:.1f}s")
+    
+    if failed == 0:
+        print("\n🎉 All coordination tests passed!")
+        sys.exit(0)
+    else:
+        print(f"\n⚠️  {failed} test(s) failed")
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()