feat: initial commit — Billo Release Agent (LangGraph)

LangGraph-based release automation agent with:
- PR discovery (webhook + polling)
- AI code review via Claude Code CLI (subscription-based)
- Auto-create Jira tickets for PRs without ticket ID
- Jira ticket lifecycle management (code review -> staging -> done)
- CI/CD pipeline trigger, polling, and approval gates
- Slack interactive messages with approval buttons
- Per-repo semantic versioning
- PostgreSQL persistence (threads, staging, releases)
- FastAPI API (webhooks, approvals, status, manual triggers)
- Docker Compose deployment

1069 tests, 95%+ coverage.

tests/test_exceptions.py

@@ -0,0 +1,198 @@
+"""Tests for custom exception hierarchy. Written FIRST (TDD RED phase)."""
+
+import pytest
+
+from release_agent.exceptions import (
+    AuthenticationError,
+    NotFoundError,
+    RateLimitError,
+    ReleaseAgentError,
+    ServiceError,
+    ServiceUnavailableError,
+)
+
+
+class TestReleaseAgentError:
+    """Tests for the base exception class."""
+
+    def test_is_exception(self) -> None:
+        err = ReleaseAgentError("something went wrong")
+        assert isinstance(err, Exception)
+
+    def test_message_stored(self) -> None:
+        err = ReleaseAgentError("something went wrong")
+        assert str(err) == "something went wrong"
+
+    def test_can_be_raised(self) -> None:
+        with pytest.raises(ReleaseAgentError):
+            raise ReleaseAgentError("boom")
+
+
+class TestServiceError:
+    """Tests for ServiceError with service name and status code."""
+
+    def test_is_release_agent_error(self) -> None:
+        err = ServiceError(service="jira", status_code=500, detail="Internal error")
+        assert isinstance(err, ReleaseAgentError)
+
+    def test_stores_service(self) -> None:
+        err = ServiceError(service="jira", status_code=500, detail="Internal error")
+        assert err.service == "jira"
+
+    def test_stores_status_code(self) -> None:
+        err = ServiceError(service="azdo", status_code=422, detail="Unprocessable")
+        assert err.status_code == 422
+
+    def test_stores_detail(self) -> None:
+        err = ServiceError(service="slack", status_code=400, detail="Bad payload")
+        assert err.detail == "Bad payload"
+
+    def test_str_includes_service_and_status(self) -> None:
+        err = ServiceError(service="jira", status_code=500, detail="Server error")
+        text = str(err)
+        assert "jira" in text
+        assert "500" in text
+
+    def test_can_be_raised(self) -> None:
+        with pytest.raises(ServiceError):
+            raise ServiceError(service="azdo", status_code=400, detail="bad request")
+
+    def test_detail_none_allowed(self) -> None:
+        err = ServiceError(service="jira", status_code=404, detail=None)
+        assert err.detail is None
+
+
+class TestAuthenticationError:
+    """Tests for AuthenticationError (401/403)."""
+
+    def test_is_service_error(self) -> None:
+        err = AuthenticationError(service="azdo")
+        assert isinstance(err, ServiceError)
+
+    def test_default_status_code_401(self) -> None:
+        err = AuthenticationError(service="azdo")
+        assert err.status_code == 401
+
+    def test_service_stored(self) -> None:
+        err = AuthenticationError(service="jira")
+        assert err.service == "jira"
+
+    def test_custom_status_code(self) -> None:
+        err = AuthenticationError(service="azdo", status_code=403)
+        assert err.status_code == 403
+
+    def test_str_contains_service(self) -> None:
+        err = AuthenticationError(service="slack")
+        assert "slack" in str(err)
+
+    def test_can_be_raised(self) -> None:
+        with pytest.raises(AuthenticationError):
+            raise AuthenticationError(service="azdo")
+
+    def test_caught_as_service_error(self) -> None:
+        with pytest.raises(ServiceError):
+            raise AuthenticationError(service="azdo")
+
+
+class TestNotFoundError:
+    """Tests for NotFoundError (404)."""
+
+    def test_is_service_error(self) -> None:
+        err = NotFoundError(service="azdo", detail="PR not found")
+        assert isinstance(err, ServiceError)
+
+    def test_status_code_is_404(self) -> None:
+        err = NotFoundError(service="jira", detail="Issue not found")
+        assert err.status_code == 404
+
+    def test_detail_stored(self) -> None:
+        err = NotFoundError(service="azdo", detail="PR 999 not found")
+        assert "PR 999" in err.detail
+
+    def test_can_be_raised(self) -> None:
+        with pytest.raises(NotFoundError):
+            raise NotFoundError(service="azdo", detail="not found")
+
+    def test_caught_as_release_agent_error(self) -> None:
+        with pytest.raises(ReleaseAgentError):
+            raise NotFoundError(service="jira", detail="issue missing")
+
+
+class TestRateLimitError:
+    """Tests for RateLimitError (429) with retry_after."""
+
+    def test_is_service_error(self) -> None:
+        err = RateLimitError(service="jira", retry_after=30)
+        assert isinstance(err, ServiceError)
+
+    def test_status_code_is_429(self) -> None:
+        err = RateLimitError(service="jira", retry_after=30)
+        assert err.status_code == 429
+
+    def test_stores_retry_after(self) -> None:
+        err = RateLimitError(service="slack", retry_after=60)
+        assert err.retry_after == 60
+
+    def test_retry_after_none_allowed(self) -> None:
+        err = RateLimitError(service="azdo", retry_after=None)
+        assert err.retry_after is None
+
+    def test_str_contains_service(self) -> None:
+        err = RateLimitError(service="jira", retry_after=5)
+        assert "jira" in str(err)
+
+    def test_can_be_raised(self) -> None:
+        with pytest.raises(RateLimitError):
+            raise RateLimitError(service="jira", retry_after=30)
+
+
+class TestServiceUnavailableError:
+    """Tests for ServiceUnavailableError (503)."""
+
+    def test_is_service_error(self) -> None:
+        err = ServiceUnavailableError(service="azdo")
+        assert isinstance(err, ServiceError)
+
+    def test_status_code_is_503(self) -> None:
+        err = ServiceUnavailableError(service="azdo")
+        assert err.status_code == 503
+
+    def test_service_stored(self) -> None:
+        err = ServiceUnavailableError(service="slack")
+        assert err.service == "slack"
+
+    def test_custom_detail(self) -> None:
+        err = ServiceUnavailableError(service="azdo", detail="Maintenance window")
+        assert "Maintenance" in err.detail
+
+    def test_can_be_raised(self) -> None:
+        with pytest.raises(ServiceUnavailableError):
+            raise ServiceUnavailableError(service="azdo")
+
+    def test_caught_as_service_error(self) -> None:
+        with pytest.raises(ServiceError):
+            raise ServiceUnavailableError(service="jira")
+
+
+class TestExceptionHierarchyInheritance:
+    """Tests verifying the full exception hierarchy is correct."""
+
+    def test_all_are_release_agent_errors(self) -> None:
+        errors = [
+            AuthenticationError(service="svc"),
+            NotFoundError(service="svc", detail="x"),
+            RateLimitError(service="svc", retry_after=1),
+            ServiceUnavailableError(service="svc"),
+        ]
+        for err in errors:
+            assert isinstance(err, ReleaseAgentError), f"{type(err)} not ReleaseAgentError"
+
+    def test_all_are_service_errors(self) -> None:
+        errors = [
+            AuthenticationError(service="svc"),
+            NotFoundError(service="svc", detail="x"),
+            RateLimitError(service="svc", retry_after=1),
+            ServiceUnavailableError(service="svc"),
+        ]
+        for err in errors:
+            assert isinstance(err, ServiceError), f"{type(err)} not ServiceError"