feat(serve): hot-reload service repos on a timer without a restart

Add serve.services_refresh_interval; refresh pulls the repos and re-imports only the changed services, staging any with active jobs until they finish. Report skipped/broken services in the log and on /api/services.

tests/core/test_services_reload.py

@@ -0,0 +1,74 @@
+"""Pins hot-reload of services: re-import on change, drop on removal, and staged swaps for busy services."""
+
+from __future__ import annotations
+
+import os
+import shutil
+import time
+from pathlib import Path
+
+import pytest
+
+from unshackle.core import services
+from unshackle.core.config import config
+
+pytestmark = pytest.mark.unit
+
+
+def write_service(root: Path, version: int) -> None:
+    pkg = root / "FOO"
+    pkg.mkdir(exist_ok=True)
+    init = pkg / "__init__.py"
+    init.write_text(f"class FOO:\n    VERSION = {version}\n    ALIASES = ('foo{version}',)\n")
+    # the bytecode cache keys on mtime and size; same-second rewrites of equal length would reuse the stale .pyc
+    os.utime(init, (time.time() + version, time.time() + version))
+
+
+@pytest.fixture
+def service_dir(tmp_path: Path, monkeypatch: pytest.MonkeyPatch):
+    root = tmp_path / "svc"
+    root.mkdir()
+    write_service(root, 1)
+    monkeypatch.setattr(config.directories, "services", [str(root)])
+    monkeypatch.setattr(services, "SERVICES", [])
+    monkeypatch.setattr(services, "MODULES", {})
+    monkeypatch.setattr(services, "ALIASES", {})
+    monkeypatch.setattr(services, "LOAD_ERRORS", [])
+    monkeypatch.setattr(services, "PENDING", set())
+    assert services.reload_services(["FOO"]) == []
+    assert services.MODULES["FOO"].VERSION == 1
+    yield root
+    services.reload_services(["FOO"])
+
+
+def test_reload_picks_up_new_code_and_removal(service_dir: Path):
+    write_service(service_dir, 2)
+    assert services.reload_services(["FOO"]) == []
+    assert services.MODULES["FOO"].VERSION == 2
+    assert services.ALIASES["FOO"] == ("foo2",)
+    assert services.Services.get_tag("foo2") == "FOO"
+
+    shutil.rmtree(service_dir / "FOO")
+    assert services.reload_services(["FOO"]) == []
+    assert "FOO" not in services.MODULES
+    assert "FOO" not in services.Services.get_tags()
+
+
+def test_busy_service_is_staged_then_applied(service_dir: Path, monkeypatch: pytest.MonkeyPatch):
+    write_service(service_dir, 2)
+    monkeypatch.setattr(services, "repo_specs", lambda: ["example/repo"])
+    monkeypatch.setattr(services, "refresh_repo", lambda spec: (service_dir, ["~FOO"]))
+
+    repos = services.refresh_and_reload(busy={"FOO"})
+    assert repos == [
+        {"spec": "example/repo", "updated": True, "changes": ["~FOO"], "deferred": ["FOO"], "load_errors": []}
+    ]
+    assert services.MODULES["FOO"].VERSION == 1
+    assert "FOO" in services.PENDING
+
+    assert services.apply_pending(busy={"FOO"}) == []
+    assert services.MODULES["FOO"].VERSION == 1
+
+    assert services.apply_pending(busy=set()) == ["FOO"]
+    assert services.MODULES["FOO"].VERSION == 2
+    assert services.PENDING == set()