fix(notes): defensively unwrap list-shaped Notes responses (refs #730)

Notes app v5.0.0 has scenarios where the API returns a JSON list where the
MCP server expects a single note object — notably the notes_api#fail
catch-all returning [] for unmatched routes. Without a guard, callers hit
a cryptic Pydantic "argument after ** must be a mapping, not list" from
Note(**payload).

Add a small _expect_note_object helper at the client layer:
- dict → pass through (the healthy case)
- single-element list → unwrap and warn (Notes v5.0.0 quirk)
- empty list, multi-element list, non-dict → raise a diagnostic ValueError
  that names the operation and points at the likely root cause (URL prefix,
  unmatched route, wrong API version)

Wire it into get_note / create_note / update so any list-shaped response
fails clearly instead of cryptically.

Six unit tests pin every branch of the helper.

Note: The 405s the issue reports for update_note / append_content match
Notes v5.0.0's documented routes (PUT /api/v1/notes/{id}) per upstream
appinfo/routes.php. They are most likely a downstream effect of #732
(missing /index.php URL prefix on installs without Pretty URLs) — the fix
in PR #733 should resolve those once it lands.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/client/test_notes.py

@@ -0,0 +1,65 @@
+"""Unit tests for the NotesClient response-shape guard.
+
+Notes app v5.0.0 has cases where the API returns a list-shaped JSON payload
+where the MCP server expects a single note object — see issue #730. The
+``_expect_note_object`` helper coerces these and surfaces clear errors instead
+of letting Pydantic raise the cryptic ``"argument after ** must be a mapping,
+not list"``.
+"""
+
+import pytest
+
+from nextcloud_mcp_server.client.notes import _expect_note_object
+
+pytestmark = pytest.mark.unit
+
+
+def test_dict_payload_passes_through():
+    """The healthy case: API returns a single note object — return it unchanged."""
+    payload = {"id": 1, "title": "Test", "content": "body", "etag": "abc"}
+    assert _expect_note_object(payload, operation="create_note") is payload
+
+
+def test_single_element_list_is_unwrapped(caplog):
+    """Notes v5.0.0 sometimes wraps a single note in a list; unwrap it and
+    log a warning so operators notice the upstream quirk.
+    """
+    inner = {"id": 1, "title": "Test", "etag": "abc"}
+    with caplog.at_level("WARNING"):
+        result = _expect_note_object([inner], operation="create_note")
+    assert result is inner
+    assert any("single-element list" in r.message for r in caplog.records)
+
+
+def test_empty_list_raises_clear_error():
+    """notes_api#fail returns ``[]`` for unmatched routes (#730). Surface a
+    diagnostic error rather than letting Pydantic complain about ``** mapping``.
+    """
+    with pytest.raises(ValueError) as exc:
+        _expect_note_object([], operation="create_note")
+    msg = str(exc.value)
+    assert "create_note" in msg
+    assert "list-shaped payload" in msg
+    assert "notes_api#fail" in msg
+
+
+def test_multi_element_list_raises_clear_error():
+    """Defensive: a list with multiple elements is also wrong shape; bail loudly."""
+    with pytest.raises(ValueError) as exc:
+        _expect_note_object([{"id": 1}, {"id": 2}], operation="update_note")
+    assert "update_note" in str(exc.value)
+
+
+def test_non_dict_non_list_raises_clear_error():
+    """Defensive: a string / int / None payload is also unexpected."""
+    with pytest.raises(ValueError) as exc:
+        _expect_note_object("not a note", operation="create_note")
+    assert "unexpected payload type" in str(exc.value)
+    assert "str" in str(exc.value)
+
+
+def test_list_of_non_dict_raises_clear_error():
+    """A list whose element isn't a dict still fails with a clear error."""
+    with pytest.raises(ValueError) as exc:
+        _expect_note_object(["not a note"], operation="get_note")
+    assert "list-shaped payload" in str(exc.value)