Add multi-agent race condition test (bd-zo7o)

- Created test_agent_race.py with 3 test scenarios
- Tests collision prevention with Agent Mail reservations
- Validates that only one agent claims an issue when reservations active
- Demonstrates collision problem when Agent Mail disabled
- Includes stress test with 10 agents
- Non-interactive mode support for CI/automation

Amp-Thread-ID: https://ampcode.com/threads/T-2fb10899-490f-4d41-b003-8bc4d467cc54
Co-authored-by: Amp <amp@ampcode.com>

tests/integration/README.md

@@ -0,0 +1,42 @@
+# Integration Tests
+
+This directory contains integration tests for bd (beads) that test end-to-end functionality.
+
+## Tests
+
+### test_agent_race.py
+
+Multi-agent race condition test that validates collision prevention with Agent Mail.
+
+**What it tests:**
+- Multiple agents simultaneously attempting to claim the same issue
+- WITH Agent Mail: Only one agent succeeds (via reservation)
+- WITHOUT Agent Mail: Multiple agents may succeed (collision)
+- Verification via JSONL that no duplicate claims occur
+
+**Prerequisites:**
+- bd installed: `go install github.com/steveyegge/beads/cmd/bd@latest`
+- Agent Mail server running (optional, for full test suite):
+  ```bash
+  cd ~/src/mcp_agent_mail
+  source .venv/bin/activate
+  uv run python -m mcp_agent_mail.cli serve-http
+  ```
+
+**Running:**
+```bash
+python3 tests/integration/test_agent_race.py
+```
+
+**Expected results:**
+- **WITH Agent Mail running:** Test 1 passes (only 1 claim), Test 2 shows collision, Test 3 passes
+- **WITHOUT Agent Mail running:** All tests demonstrate collision (expected behavior without reservation system)
+
+## Adding New Tests
+
+Integration tests should:
+1. Use temporary workspaces (cleaned up automatically)
+2. Test real bd CLI commands, not just internal APIs
+3. Verify behavior in `.beads/issues.jsonl` when relevant
+4. Clean up resources in `finally` blocks
+5. Provide clear output showing what's being tested