fix(service): make expected_version mandatory on update_note and edit

Both guarded with `if expected_version and ...`, so an empty string
skipped the version check entirely and silently overwrote the note.
Empty/missing expected_version is now a structured INVALID error.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0139vHnNpS2sLNELjrAHX5Cu

src/mdmem/service.py

@@ -426,7 +426,9 @@ class MemoryService:
         """Active notes are never edited in place by an agent: the edit becomes a
         proposed revision in the inbox (§2.4, §9)."""
         note = self.get_note(note_id)
-        if expected_version and expected_version != note.file_hash:
+        if not expected_version:
+            raise Invalid("expected_version is required; read the note first and pass its version", id=note_id)
+        if expected_version != note.file_hash:
             raise VersionConflict(note_id, expected_version, note.file_hash)
         if note.state == "archive":
             raise Archived(note_id)
@@ -587,7 +589,9 @@ class MemoryService:
     ) -> dict[str, Any]:
         """Direct edit from the UI: the owner may change an active note in place."""
         note = self.get_note(note_id)
-        if expected_version and expected_version != note.file_hash:
+        if not expected_version:
+            raise Invalid("expected_version is required; read the note first and pass its version", id=note_id)
+        if expected_version != note.file_hash:
             raise VersionConflict(note_id, expected_version, note.file_hash)
         if frontmatter:
             for k, v in frontmatter.items():

tests/test_service_writes.py

@@ -32,3 +32,24 @@ async def test_update_note_on_a_rejected_archived_note_is_refused(svc):
     unchanged = svc.get_note(w["id"])
     assert unchanged.body.strip() == "alt"
     assert unchanged.get("rejected") is True
+
+
+# -- finding 4: expected_version must be mandatory, not just "truthy" ---------
+async def test_update_note_with_empty_expected_version_is_rejected(svc):
+    w = await svc.write_note(title="T", body="original", type="note")
+
+    with pytest.raises(Invalid):
+        await svc.update_note(w["id"], "", body="entfuehrt")
+
+    unchanged = svc.get_note(w["id"])
+    assert unchanged.body.strip() == "original"
+
+
+async def test_edit_with_empty_expected_version_is_rejected(svc):
+    w = await svc.write_note(title="T", body="original", type="note")
+
+    with pytest.raises(Invalid):
+        await svc.edit(w["id"], body="entfuehrt", expected_version="")
+
+    unchanged = svc.get_note(w["id"])
+    assert unchanged.body.strip() == "original"