fix(tests): a Result's .all() is sync, and the module has a fourth tool (#4104)

Two failures in the tests added with the step, both mine.

`make_mock_session` is an AsyncMock and every child of an AsyncMock is one too,
so leaving `.all` as it came handed `migrate_floor` a coroutine where it reads a
list — the same trap the helper's own docstring already flags for `add`.

And the registration test enumerated three tools by name, which is exactly what
it is for: `migrate_retrieval_floor` made it four.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

tests/test_retrieval_migration.py

@@ -32,8 +32,14 @@ def _logs(pairs):
 
 
 def _session_with(rows):
+    """`.all()` is SYNCHRONOUS on a Result, so it needs a MagicMock.
+
+    `make_mock_session` is an AsyncMock, and every child of an AsyncMock is one
+    too — leaving `.all` as it comes hands the service a coroutine where it
+    expects a list, the same trap the helper's docstring flags for `add`.
+    """
     session = make_mock_session()
-    session.execute.return_value.all.return_value = rows
+    session.execute.return_value = MagicMock(all=MagicMock(return_value=rows))
     return session