feat: add StorageAdapter abstraction and InMemoryAdapter with full test suite

- Introduce StorageAdapter protocol and InMemoryAdapter (thread-safe, in-memory)
  in engine/adapter.py to decouple storage from sync logic
- Refactor SyncEngine to accept a StorageAdapter, replacing the previous
  stub that returned an empty list
- Wire server to use SyncEngine + InMemoryAdapter, removing hardcoded
  SYNC_OPERATIONS fixtures
- Add tests for engine, adapter, generator, and types (tests/)
- Add pre-commit config (.pre-commit-config.yaml) with linting/formatting hooks
- Update pyproject.toml and uv.lock with new dev dependencies
- Clean up type annotations and CLI help strings across generator, server, and utils

tests/test_adapter.py

@@ -0,0 +1,148 @@
+"""Tests for engine.adapter — InMemoryAdapter and StorageAdapter protocol."""
+
+import threading
+
+from engine.adapter import InMemoryAdapter
+from engine.types.operation import Operation
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def make_op(**kwargs: object) -> Operation:
+    defaults: dict[str, object] = {
+        "type": "insert",
+        "device_id": "dev-1",
+        "timestamp": "1000000.0",
+        "entity_id": "e1",
+        "entity_type": "obj",
+        "payload": {"key": "value"},
+    }
+    defaults.update(kwargs)
+    return Operation(**defaults)
+
+
+# ---------------------------------------------------------------------------
+# Initial state
+# ---------------------------------------------------------------------------
+
+
+class TestInMemoryAdapterInit:
+    def test_cursor_starts_at_zero(self) -> None:
+        adapter = InMemoryAdapter()
+        assert adapter.cursor == 0
+
+    def test_get_all_returns_empty_on_fresh_adapter(self) -> None:
+        adapter = InMemoryAdapter()
+        assert adapter.get_operations_after(0) == []
+
+
+# ---------------------------------------------------------------------------
+# append_operations
+# ---------------------------------------------------------------------------
+
+
+class TestAppendOperations:
+    def test_returns_new_cursor(self) -> None:
+        adapter = InMemoryAdapter()
+        cursor = adapter.append_operations([make_op(), make_op()])
+        assert cursor == 2
+
+    def test_empty_append_returns_current_cursor(self) -> None:
+        adapter = InMemoryAdapter()
+        adapter.append_operations([make_op()])
+        cursor = adapter.append_operations([])
+        assert cursor == 1
+
+    def test_sequential_ids_are_stamped(self) -> None:
+        adapter = InMemoryAdapter()
+        adapter.append_operations([make_op(), make_op(), make_op()])
+        ids = [op.id for op in adapter._log]
+        assert ids == ["1", "2", "3"]
+
+    def test_original_op_id_is_overwritten(self) -> None:
+        """Server always assigns its own sequence number."""
+        adapter = InMemoryAdapter()
+        adapter.append_operations([make_op(id="client-assigned-id")])
+        assert adapter._log[0].id == "1"
+
+    def test_original_op_fields_preserved(self) -> None:
+        adapter = InMemoryAdapter()
+        op = make_op(entity_id="entity-42", payload={"hello": "world"})
+        adapter.append_operations([op])
+        stored = adapter._log[0]
+        assert stored.entity_id == "entity-42"
+        assert stored.payload == {"hello": "world"}
+
+    def test_cursor_advances_incrementally(self) -> None:
+        adapter = InMemoryAdapter()
+        c1 = adapter.append_operations([make_op()])
+        c2 = adapter.append_operations([make_op()])
+        c3 = adapter.append_operations([make_op()])
+        assert c1 == 1
+        assert c2 == 2
+        assert c3 == 3
+
+
+# ---------------------------------------------------------------------------
+# get_operations_after
+# ---------------------------------------------------------------------------
+
+
+class TestGetOperationsAfter:
+    def test_cursor_zero_returns_all(self) -> None:
+        adapter = InMemoryAdapter()
+        adapter.append_operations([make_op(), make_op()])
+        ops = adapter.get_operations_after(0)
+        assert len(ops) == 2
+
+    def test_cursor_at_end_returns_empty(self) -> None:
+        adapter = InMemoryAdapter()
+        adapter.append_operations([make_op(), make_op()])
+        ops = adapter.get_operations_after(2)
+        assert ops == []
+
+    def test_cursor_in_middle_returns_tail(self) -> None:
+        adapter = InMemoryAdapter()
+        adapter.append_operations([make_op(), make_op(), make_op()])
+        ops = adapter.get_operations_after(1)
+        assert len(ops) == 2
+        assert ops[0].id == "2"
+        assert ops[1].id == "3"
+
+    def test_returns_copy_not_reference(self) -> None:
+        """Mutating the returned list must not affect the internal log."""
+        adapter = InMemoryAdapter()
+        adapter.append_operations([make_op()])
+        ops = adapter.get_operations_after(0)
+        ops.clear()
+        assert len(adapter._log) == 1
+
+
+# ---------------------------------------------------------------------------
+# Thread safety
+# ---------------------------------------------------------------------------
+
+
+class TestThreadSafety:
+    def test_concurrent_appends_produce_unique_sequential_ids(self) -> None:
+        adapter = InMemoryAdapter()
+        errors: list[Exception] = []
+
+        def worker() -> None:
+            try:
+                adapter.append_operations([make_op()])
+            except Exception as exc:
+                errors.append(exc)
+
+        threads = [threading.Thread(target=worker) for _ in range(50)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
+        assert errors == [], f"Thread errors: {errors}"
+        assert adapter.cursor == 50
+        ids = {op.id for op in adapter._log}
+        assert ids == {str(i) for i in range(1, 51)}