diff --git a/custom_components/nestquest/db.py b/custom_components/nestquest/db.py
index bd785a4..c05af6b 100644
--- a/custom_components/nestquest/db.py
+++ b/custom_components/nestquest/db.py
@@ -110,7 +110,16 @@ class NestQuestDatabase:
             yield
 
     async def open(self, path: Path | str) -> NestQuestDatabase:
-        """Open the SQLite file with WAL journal mode and foreign keys on."""
+        """Open the SQLite file with WAL journal mode and foreign keys on.
+
+        Cancellation-safe: if this call is cancelled while the connect job
+        is in flight, the job still settles (see :meth:`_await_settled`).
+        A connection the settled job created is never adopted by the
+        cancelled call; it is closed through a settled executor job instead
+        of being abandoned to garbage collection, and the cancellation
+        propagates afterwards, so a follow-up ``open()`` starts from a
+        clean state.
+        """
         if self._conn is not None:
             return self
         async with self._get_lock():
@@ -129,9 +138,20 @@ class NestQuestDatabase:
                     raise
                 return conn
 
-            self._conn = await self._await_settled(
+            settled, cancelled = await self._await_settled_state(
                 self._hass.async_add_executor_job(_open)
             )
+            if cancelled:
+                if isinstance(settled, sqlite3.Connection):
+
+                    def _close_abandoned() -> None:
+                        settled.close()
+
+                    await self._await_settled(
+                        self._hass.async_add_executor_job(_close_abandoned)
+                    )
+                raise asyncio.CancelledError()
+            self._conn = settled
         return self
 
     async def execute(
@@ -336,6 +356,20 @@ class NestQuestDatabase:
         settlement is absorbed the same way; if the job itself fails after
         a cancellation, both errors surface in an ExceptionGroup.
         """
+        result, cancelled = await self._await_settled_state(job)
+        if cancelled:
+            raise asyncio.CancelledError()
+        return result
+
+    async def _await_settled_state(self, job: Awaitable[Any]) -> tuple[Any, bool]:
+        """Await ``job`` to settlement and report ``(result, cancelled)``.
+
+        Same settlement guarantees as :meth:`_await_settled`, but returns
+        the settled outcome together with whether the awaiting task was
+        cancelled, so callers that must act on a settled result before
+        re-raising cancellation (e.g. closing an abandoned connection)
+        can do so without losing the result.
+        """
         cancelled = False
         inner = asyncio.ensure_future(job)
         while not inner.done():
@@ -352,9 +386,7 @@ class NestQuestDatabase:
                     [asyncio.CancelledError(), job_error],
                 ) from job_error
             raise
-        if cancelled:
-            raise asyncio.CancelledError()
-        return result
+        return result, cancelled
 
     async def close(self) -> None:
         """Close the connection in the executor; safe to call repeatedly.
diff --git a/tests/test_db.py b/tests/test_db.py
index 8aceb8c..7640c57 100644
--- a/tests/test_db.py
+++ b/tests/test_db.py
@@ -406,6 +406,71 @@ async def test_commit_failure_rolls_back_and_next_transaction_works(
     await database.close()
 
 
+async def test_cancel_during_open_closes_abandoned_connection(tmp_path) -> None:
+    """NQ-PR12-010: cancel during open() must close the settled connection.
+
+    The _open executor job is gated: the open task is cancelled while the
+    connect is still in flight, then the worker is allowed to complete it
+    anyway.  The settled connection must never be adopted, must be closed
+    through a settled executor-backed close before the cancellation
+    propagates, and a follow-up open() must succeed cleanly.
+    """
+    hass, _registry = make_hass()
+    database = NestQuestDatabase(hass)
+
+    open_started = asyncio.Event()
+    release_open = asyncio.Event()
+    jobs: list[str] = []
+    captured: dict[str, Any] = {}
+    real_add = hass.async_add_executor_job
+
+    async def _gated_add_executor_job(fn, *args, **kwargs):
+        name = getattr(fn, "__name__", "")
+        jobs.append(name)
+        if name == "_open":
+            open_started.set()
+            await release_open.wait()
+        result = await real_add(fn, *args, **kwargs)
+        if name == "_open":
+            captured["conn"] = result
+        return result
+
+    hass.async_add_executor_job = _gated_add_executor_job
+
+    open_task = asyncio.create_task(database.open(tmp_path / "cancel-open.db"))
+    await open_started.wait()
+    open_task.cancel()
+    await asyncio.sleep(0.05)
+    assert database._conn is None, (
+        "the cancelled open adopted a connection that was still settling"
+    )
+    release_open.set()
+    with pytest.raises(asyncio.CancelledError):
+        await open_task
+
+    assert database.connected is False
+    assert "_close_abandoned" in jobs, (
+        "the abandoned connection was not closed via an executor job"
+    )
+    conn = captured.get("conn")
+    assert conn is not None
+
+    def _probe() -> str:
+        try:
+            conn.execute("SELECT 1")
+        except sqlite3.ProgrammingError:
+            return "closed"
+        return "open"
+
+    assert await real_add(_probe) == "closed"
+
+    hass.async_add_executor_job = real_add
+    await database.open(tmp_path / "cancel-open.db")
+    assert database.connected is True
+    assert await database.fetch_one("SELECT 1") == (1,)
+    await database.close()
+
+
 async def test_cancel_during_begin_settles_then_rolls_back(tmp_path) -> None:
     """NQ-PR12-007: cancel during BEGIN must not leak a stray transaction.