fix(webdav): address PR #764 review round 4

- Guard against malformed PROPFIND responses where tag["id"] is None
  before calling get_files_by_tag (prevents
  <oc:systemtag>None</oc:systemtag> dispatch).
- Add OCS-APIRequest: true header to get_tag_by_name and
  get_files_by_tag to match every other PROPFIND/REPORT in the file —
  fixes a latent reverse-proxy compatibility hazard.
- Add test_copy_resource_blocks_excluded_source to mirror the
  existing move-source coverage; closes the asymmetric test gap.
- Add test_skips_tag_with_missing_id covering the new fail-open
  branch in _resolve_one_tag.
- Reword _resolve_one_tag docstring: "distinct slot" was misleading
  (tasks append rather than pre-allocate).

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

nextcloud_mcp_server/client/webdav.py

@@ -1135,7 +1135,11 @@ class WebDAVClient(BaseNextcloudClient):
         response = await self._make_request(
             "PROPFIND",
             "/remote.php/dav/systemtags/",
-            headers={"Depth": "1", "Content-Type": "text/xml"},
+            headers={
+                "Depth": "1",
+                "Content-Type": "text/xml",
+                "OCS-APIRequest": "true",
+            },
             content=propfind_body,
         )
         # Redundant after _make_request (which raises on non-2xx) but
@@ -1223,7 +1227,7 @@ class WebDAVClient(BaseNextcloudClient):
         response = await self._make_request(
             "REPORT",
             f"{self._get_webdav_base_path()}/",
-            headers={"Content-Type": "text/xml"},
+            headers={"Content-Type": "text/xml", "OCS-APIRequest": "true"},
             content=report_body,
         )
         # Redundant after _make_request (which raises on non-2xx) but

nextcloud_mcp_server/server/tag_exclusion.py

@@ -46,11 +46,11 @@ async def _resolve_one_tag(
 ) -> None:
     """Resolve a single tag's paths and append them as a set to *results*.
 
-    Each task writes to a distinct slot in the shared list — append from
-    cooperative tasks is safe under anyio (single-threaded between
-    awaits) without an explicit lock. Swallows its own exceptions so a
-    failure for one tag does not abort the surrounding task group
-    (preserves fail-open per-tag semantics).
+    Each task appends its own set to the shared list; ``list.append`` is
+    atomic between cooperative yields under anyio (single-threaded
+    between awaits) so no explicit lock is needed. Swallows its own
+    exceptions so a failure for one tag does not abort the surrounding
+    task group (preserves fail-open per-tag semantics).
     """
     try:
         tag = await webdav.get_tag_by_name(tag_name)
@@ -67,6 +67,15 @@ async def _resolve_one_tag(
         logger.debug("Excluded tag %r does not exist — skipping", tag_name)
         return
 
+    if tag.get("id") is None:
+        # Malformed PROPFIND response: <oc:systemtag> entry without
+        # <oc:id/>. Skip rather than dispatch <oc:systemtag>None</oc:systemtag>.
+        logger.debug(
+            "Excluded tag %r has no id in PROPFIND response — skipping",
+            tag_name,
+        )
+        return
+
     try:
         files = await webdav.get_files_by_tag(tag["id"])
     except Exception as e:

tests/unit/test_tag_exclusion.py

@@ -127,6 +127,32 @@ class TestGetExcludedFilePaths:
         webdav.get_tag_by_name.assert_awaited_once_with("does-not-exist")
         webdav.get_files_by_tag.assert_not_called()
 
+    @pytest.mark.unit
+    async def test_skips_tag_with_missing_id(self, mocker):
+        """If get_tag_by_name returns a dict with id=None (malformed
+        PROPFIND response — <oc:systemtag> entry without <oc:id/>), skip
+        the tag rather than dispatching <oc:systemtag>None</oc:systemtag>
+        to get_files_by_tag (PR #764 review round 4)."""
+        mocker.patch(
+            "nextcloud_mcp_server.server.tag_exclusion.get_excluded_tag_names",
+            return_value=["malformed"],
+        )
+        webdav = AsyncMock()
+        webdav.get_tag_by_name = AsyncMock(
+            return_value={
+                "id": None,
+                "name": "malformed",
+                "userVisible": True,
+                "userAssignable": True,
+            }
+        )
+
+        result = await get_excluded_file_paths(webdav)
+
+        assert result == set()
+        webdav.get_tag_by_name.assert_awaited_once_with("malformed")
+        webdav.get_files_by_tag.assert_not_called()
+
     @pytest.mark.unit
     async def test_fail_open_when_tag_lookup_raises(self, mocker, caplog):
         """If get_tag_by_name raises (e.g. 5xx from systemtags endpoint),

tests/unit/test_webdav_tools_exclusion.py

@@ -194,6 +194,23 @@ async def test_move_resource_blocks_excluded_destination_exact_match(
         )
 
 
+async def test_copy_resource_blocks_excluded_source(
+    webdav_tools, fake_client, patch_get_client, patch_excluded
+):
+    patch_get_client(fake_client)
+    patch_excluded({"Secret.txt"})
+
+    fn = webdav_tools["nc_webdav_copy_resource"].fn
+    with pytest.raises(ToolError, match="source"):
+        await fn(
+            source_path="/Secret.txt",
+            destination_path="/Public/copy.txt",
+            ctx=_mock_ctx(fake_client),
+        )
+
+    fake_client.webdav.copy_resource.assert_not_called()
+
+
 async def test_copy_resource_blocks_excluded_destination_descendant(
     webdav_tools, fake_client, patch_get_client, patch_excluded
 ):