feat(versions): rolling-cap prune ignores pinned versions

The DELETE inside create_version now filters pin_kind IS NULL so pinned
rows (auto or manual) aren't counted toward MAX_VERSIONS=50 and aren't
candidates for deletion. Pinned versions live indefinitely regardless
of how heavy rolling autosave traffic gets on the same note.

tests/test_version_pinning_prune.py

@@ -0,0 +1,45 @@
+"""Tests for the prune logic — both rolling (pin_kind IS NULL) and the
+auto-pin bucket (pin_kind='auto').
+
+Design: docs/superpowers/specs/2026-05-13-note-version-pinning-design.md
+"""
+from unittest.mock import AsyncMock, MagicMock, patch
+
+
+async def test_create_version_prune_sql_filters_to_unpinned():
+    """The DELETE statement issued by create_version's prune step must
+    include `pin_kind IS NULL` in the inner SELECT so pinned versions
+    aren't counted toward MAX_VERSIONS and can't be pruned by it."""
+    mock_session = AsyncMock()
+    select_result = MagicMock()
+    # No prior version → skips the throttle/dedupe early-return paths and
+    # proceeds straight to insert + prune.
+    select_result.scalars.return_value.first.return_value = None
+    mock_session.add = MagicMock()
+    mock_session.commit = AsyncMock()
+    mock_session.refresh = AsyncMock()
+    mock_session.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_session.__aexit__ = AsyncMock(return_value=False)
+
+    captured_sql: list[str] = []
+
+    async def execute_capture(stmt, *args, **kwargs):
+        captured_sql.append(str(stmt))
+        if len(captured_sql) == 1:
+            return select_result
+        return MagicMock()
+
+    mock_session.execute = AsyncMock(side_effect=execute_capture)
+
+    with patch(
+        "fabledassistant.services.note_versions.async_session",
+        return_value=mock_session,
+    ):
+        from fabledassistant.services.note_versions import create_version
+        await create_version(
+            user_id=1, note_id=42, body="content", title="t", tags=["a"],
+        )
+
+    assert any("pin_kind IS NULL" in s for s in captured_sql), (
+        f"Expected prune SQL to filter pin_kind IS NULL; got: {captured_sql!r}"
+    )