test: Add integration tests documenting DeckClient.update_card bugs

Tests document current behavior of update_card method:
- Updating without title fails (400) - title required but conditionally sent
- Updating with title clears description - PUT is full replacement

Related: #452

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/client/deck/test_deck_update_card_api.py

@@ -0,0 +1,200 @@
+"""
+Integration tests for DeckClient.update_card API behavior.
+
+This test suite documents the behavior of our DeckClient.update_card method
+and identifies bugs in how it handles partial updates.
+
+FINDINGS:
+The Deck API PUT endpoint is a FULL REPLACEMENT, not a partial update.
+Fields not included in the request body are either:
+- Required and cause 400 error (title, type, owner)
+- Optional but get CLEARED if not sent (description)
+
+Related issues:
+- nextcloud-mcp-server #452: DeckClient.update_card always sets owner/type
+- deck #3127: REST API Docs: missing parameter in "update cards"
+- deck #4106: Provide a working example of API usage to update a cards details
+"""
+
+import httpx
+import pytest
+
+pytestmark = [pytest.mark.integration]
+
+
+@pytest.fixture
+async def deck_test_card(nc_client):
+    """Create a board, stack, and card for testing, cleanup after."""
+    board = await nc_client.deck.create_board("Test Update Card API", "FF0000")
+    stack = await nc_client.deck.create_stack(board.id, "Test Stack", 1)
+    card = await nc_client.deck.create_card(
+        board.id,
+        stack.id,
+        "Original Title",
+        type="plain",
+        description="Original description",
+    )
+
+    yield {
+        "board_id": board.id,
+        "stack_id": stack.id,
+        "card_id": card.id,
+        "card": card,
+    }
+
+    # Cleanup
+    await nc_client.deck.delete_board(board.id)
+
+
+class TestDeckClientUpdateCard:
+    """
+    Test DeckClient.update_card() method behavior with various parameter combinations.
+
+    These tests document the current buggy behavior where:
+    1. Updating without title fails (400) - title is required but conditionally sent
+    2. Updating with title clears description - description should be preserved
+    """
+
+    async def test_update_title_only_clears_description(
+        self, nc_client, deck_test_card
+    ):
+        """
+        BUG: Updating only the title clears the description.
+
+        The Deck PUT API is a full replacement. Our client doesn't send
+        description when not explicitly provided, so it gets cleared.
+        """
+        await nc_client.deck.update_card(
+            board_id=deck_test_card["board_id"],
+            stack_id=deck_test_card["stack_id"],
+            card_id=deck_test_card["card_id"],
+            title="New Title",
+        )
+
+        updated = await nc_client.deck.get_card(
+            deck_test_card["board_id"],
+            deck_test_card["stack_id"],
+            deck_test_card["card_id"],
+        )
+        assert updated.title == "New Title"
+        # BUG: Description was cleared instead of preserved
+        assert updated.description == ""  # Should be "Original description"
+
+    async def test_update_description_only_fails(self, nc_client, deck_test_card):
+        """
+        BUG: Updating only the description fails with 400.
+
+        The Deck PUT API requires title, type, and owner.
+        Our client doesn't send title when not explicitly provided.
+        """
+        with pytest.raises(httpx.HTTPStatusError) as exc_info:
+            await nc_client.deck.update_card(
+                board_id=deck_test_card["board_id"],
+                stack_id=deck_test_card["stack_id"],
+                card_id=deck_test_card["card_id"],
+                description="New description only",
+            )
+
+        assert exc_info.value.response.status_code == 400
+
+    async def test_update_title_and_description(self, nc_client, deck_test_card):
+        """Updating title and description together works correctly."""
+        await nc_client.deck.update_card(
+            board_id=deck_test_card["board_id"],
+            stack_id=deck_test_card["stack_id"],
+            card_id=deck_test_card["card_id"],
+            title="New Title",
+            description="New description",
+        )
+
+        updated = await nc_client.deck.get_card(
+            deck_test_card["board_id"],
+            deck_test_card["stack_id"],
+            deck_test_card["card_id"],
+        )
+        assert updated.title == "New Title"
+        assert updated.description == "New description"
+
+    async def test_update_duedate_only_fails(self, nc_client, deck_test_card):
+        """
+        BUG: Updating only the duedate fails with 400.
+
+        title is required but not sent when not explicitly provided.
+        """
+        with pytest.raises(httpx.HTTPStatusError) as exc_info:
+            await nc_client.deck.update_card(
+                board_id=deck_test_card["board_id"],
+                stack_id=deck_test_card["stack_id"],
+                card_id=deck_test_card["card_id"],
+                duedate="2025-12-31T23:59:59+00:00",
+            )
+
+        assert exc_info.value.response.status_code == 400
+
+    async def test_update_archived_only_fails(self, nc_client, deck_test_card):
+        """
+        BUG: Updating only the archived status fails with 400.
+
+        title is required but not sent when not explicitly provided.
+        """
+        with pytest.raises(httpx.HTTPStatusError) as exc_info:
+            await nc_client.deck.update_card(
+                board_id=deck_test_card["board_id"],
+                stack_id=deck_test_card["stack_id"],
+                card_id=deck_test_card["card_id"],
+                archived=True,
+            )
+
+        assert exc_info.value.response.status_code == 400
+
+    async def test_update_preserves_type(self, nc_client, deck_test_card):
+        """Type is correctly preserved (already always sent in current implementation)."""
+        original = deck_test_card["card"]
+
+        await nc_client.deck.update_card(
+            board_id=deck_test_card["board_id"],
+            stack_id=deck_test_card["stack_id"],
+            card_id=deck_test_card["card_id"],
+            title="Changed Title",
+        )
+
+        updated = await nc_client.deck.get_card(
+            deck_test_card["board_id"],
+            deck_test_card["stack_id"],
+            deck_test_card["card_id"],
+        )
+        assert updated.type == original.type
+
+    async def test_update_preserves_owner(self, nc_client, deck_test_card):
+        """Owner is correctly preserved (already always sent in current implementation)."""
+        original = deck_test_card["card"]
+
+        await nc_client.deck.update_card(
+            board_id=deck_test_card["board_id"],
+            stack_id=deck_test_card["stack_id"],
+            card_id=deck_test_card["card_id"],
+            title="Changed Title",
+        )
+
+        updated = await nc_client.deck.get_card(
+            deck_test_card["board_id"],
+            deck_test_card["stack_id"],
+            deck_test_card["card_id"],
+        )
+        assert updated.owner == original.owner
+
+    async def test_update_order_only_fails(self, nc_client, deck_test_card):
+        """
+        BUG: Updating only the order fails with 400.
+
+        title is required but not sent when not explicitly provided.
+        """
+        with pytest.raises(httpx.HTTPStatusError) as exc_info:
+            await nc_client.deck.update_card(
+                board_id=deck_test_card["board_id"],
+                stack_id=deck_test_card["stack_id"],
+                card_id=deck_test_card["card_id"],
+                order=1,
+            )
+
+        assert exc_info.value.response.status_code == 400