fix(vector): guard unbound doc_task + address review nits (#891)

Round-1 review on PR #891:
- Guard processor_task's broad except handler against an unbound doc_task
  (mirrors multi_user_processor_task): initialise doc_task=None before the loop
  and branch the error log. Fixes a latent NameError if receive() raises a
  non-TimeoutError/EndOfStream before the first document binds. Regression test
  added.
- Drop the unnecessary `from __future__ import annotations` in vector/_errors.py
  and express format_exception_group's non-group fast path as an explicit
  isinstance check.
- Add a copy_resource Destination-header encoding test (analogue to MOVE);
  strengthen the ExceptionGroup test to assert the full leaf repr survives.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/client/test_webdav.py

@@ -588,3 +588,23 @@ async def test_move_resource_encodes_destination_header(mocker):
     destination = call.kwargs["headers"]["Destination"]
     assert "%23" in destination
     assert "#" not in destination
+
+
+@pytest.mark.unit
+async def test_copy_resource_encodes_destination_header(mocker):
+    """The COPY Destination header must be percent-encoded too (card 309)."""
+    mock_http_client = AsyncMock()
+    client = WebDAVClient(mock_http_client, "testuser")
+
+    mock_response = AsyncMock()
+    mock_response.status_code = 201
+    mock_response.raise_for_status = mocker.Mock()
+    mock_http_client.request = AsyncMock(return_value=mock_response)
+
+    await client.copy_resource("a/old.pdf", "b/new #1.pdf")
+
+    call = mock_http_client.request.call_args
+    assert call[0][1] == "/remote.php/dav/files/testuser/a/old.pdf"
+    destination = call.kwargs["headers"]["Destination"]
+    assert "%23" in destination
+    assert "#" not in destination

tests/unit/vector/test_errors.py

@@ -22,6 +22,9 @@ def test_format_exception_group_names_leaf_cause():
     formatted = format_exception_group(group)
 
     assert "ConnectError" in formatted
+    # Assert the full leaf repr survives, not just the type name -- guards a
+    # future format change that kept the type but dropped the message.
+    assert repr(leaf) in formatted
     assert "unhandled errors in a TaskGroup" not in formatted
     assert "1 sub-exception" in formatted
 

tests/unit/vector/test_processor_task.py

@@ -0,0 +1,50 @@
+"""Regression test for processor_task's exception handler (card 309 / PR #891).
+
+If ``receive_stream.receive()`` raises something other than
+``TimeoutError``/``EndOfStream`` before any document is bound, the broad
+``except`` handler must not crash on an unbound ``doc_task`` name.
+"""
+
+from unittest.mock import MagicMock
+
+import anyio
+import pytest
+
+from nextcloud_mcp_server.vector.processor import processor_task
+
+
+class _ReceiveBoomThenEnd:
+    """First receive() raises a non-Timeout error (no doc_task bound yet); the
+    second ends the stream so the loop exits."""
+
+    def __init__(self, shutdown: anyio.Event):
+        self._calls = 0
+        self._shutdown = shutdown
+
+    async def receive(self):
+        self._calls += 1
+        if self._calls == 1:
+            raise RuntimeError("transport blew up before any document")
+        self._shutdown.set()
+        raise anyio.EndOfStream
+
+    def statistics(self):  # pragma: no cover - not reached on the error path
+        return MagicMock(current_buffer_used=0)
+
+
+@pytest.mark.unit
+async def test_processor_task_receive_error_does_not_raise_unbound(caplog):
+    shutdown = anyio.Event()
+    stream = _ReceiveBoomThenEnd(shutdown)
+
+    # Must complete without a NameError leaking out of the except handler.
+    with caplog.at_level("ERROR", logger="nextcloud_mcp_server.vector.processor"):
+        await processor_task(
+            worker_id=0,
+            receive_stream=stream,  # type: ignore[arg-type]
+            shutdown_event=shutdown,
+            nc_client=MagicMock(),
+            user_id="alice",
+        )
+
+    assert any("RuntimeError" in rec.message for rec in caplog.records)