feat(mvp): Phase 1 control layer + API vertical slice

Implements the Phase 1 MVP from the README: a stateless control layer + HTTP
API over a centralized database, with hook-enforced test/push gates.

- DB layer: SQLAlchemy Core, one schema rendering both Postgres (BIGSERIAL /
  TIMESTAMPTZ / JSONB) and SQLite (INTEGER PK / TEXT / JSON) via portable types;
  native ON CONFLICT DO UPDATE checkmark upsert on both dialects.
- Alembic dual-dialect migrations (render_as_batch for SQLite); tests run a real
  `alembic upgrade head`.
- FastAPI: projects/agents/checkmark/log/answer/resume + shared log/context
  routes, single global bearer token, higher-trust token gating shared-context
  writes, project isolation on every route.
- Hooks (`python -m handler.hooks <event>`): Stop test gate (block on red),
  PreToolUse AskUserQuestion defer + `git push` gate (tests then throwaway
  build), Notification generic webhook (no-op without WEBHOOK_URL). Identity via
  env injected at spawn; verify is the mock seam.
- Control CLI: spawn/list/attach/kill, hard `.mise.toml [tasks.test]` gate,
  generated per-agent settings.json, identity + DATABASE_URL injected via tmux;
  tmux is the mock seam.
- 45 tests (SQLite), ruff clean. Live claude/tmux/mise spawning deferred behind
  the mocked seams.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W5ZuS5pV1NS6eKsRZHXonY

tests/test_hook_checkpoint.py

@@ -0,0 +1,65 @@
+"""Stop / SessionEnd checkpoint gate."""
+
+from __future__ import annotations
+
+from handler.db import repository as repo
+from handler.hooks import checkpoint, verify
+from handler.hooks.context import HookInput, Identity
+
+
+def _seed(conn):
+    repo.create_project(conn, "p", "/tmp/p")
+    a = repo.create_agent(conn, "p", "a", "/tmp/p/a")
+    return Identity(a["id"], "p", "a", "/tmp/p/a")
+
+
+def test_stop_blocks_on_failing_tests(conn, monkeypatch):
+    ident = _seed(conn)
+    monkeypatch.setattr(verify, "run_test", lambda cwd: (False, "1 failed"))
+
+    result = checkpoint.handle_stop(conn, ident, HookInput({"session_id": "s1"}, "stop"))
+    assert result["decision"] == "block"
+    assert "test gate failed" in result["reason"]
+
+    cm = repo.get_checkmark(conn, ident.agent_id)
+    assert cm["tests_status"] == "fail"
+    assert cm["status"] == "blocked"
+    # A blocked turn never records "done".
+    assert repo.get_agent_by_name(conn, "p", "a")["status"] == "blocked"
+
+
+def test_stop_allows_done_on_passing_tests(conn, monkeypatch):
+    ident = _seed(conn)
+    monkeypatch.setattr(verify, "run_test", lambda cwd: (True, "ok"))
+
+    result = checkpoint.handle_stop(conn, ident, HookInput({"session_id": "s1"}, "stop"))
+    assert result == {}  # no block
+
+    cm = repo.get_checkmark(conn, ident.agent_id)
+    assert cm["tests_status"] == "pass"
+    assert cm["status"] == "done"
+    assert cm["log_entry_id"] is not None
+
+
+def test_stop_does_not_reblock_when_already_active(conn, monkeypatch):
+    ident = _seed(conn)
+    monkeypatch.setattr(verify, "run_test", lambda cwd: (False, "still failing"))
+    hi = HookInput({"session_id": "s1", "stop_hook_active": True}, "stop")
+    result = checkpoint.handle_stop(conn, ident, hi)
+    assert result == {}  # recorded, but not an infinite block
+    assert repo.get_checkmark(conn, ident.agent_id)["tests_status"] == "fail"
+
+
+def test_session_end_records_without_gate(conn, monkeypatch):
+    ident = _seed(conn)
+    # Even if tests would fail, SessionEnd must not run the gate or block.
+    monkeypatch.setattr(
+        verify, "run_test", lambda cwd: (_ for _ in ()).throw(AssertionError("gate ran"))
+    )
+    result = checkpoint.handle_session_end(
+        conn, ident, HookInput({"reason": "clear"}, "session_end")
+    )
+    assert result == {}
+    assert repo.get_checkmark(conn, ident.agent_id)["where_it_stopped"].startswith(
+        "session ended"
+    )