fix(download): return 200 for missing queue items and quiet download-progress 404s

The browser extension's apiFetch treats any 404 as a missing endpoint and
retries the legacy non-/api/lm URL, producing two spurious
'error_middleware - WARNING - API GET ... 404' log lines per occurrence.

- complete_download_in_queue / update_download_queue_status /
  retry_download_from_history: 'not found' is a normal business outcome,
  return 200 + success:false instead of 404 (extension behavior unchanged;
  apiGet ignores the HTTP status)
- error_middleware: downgrade /api/lm/download-progress/ 404s to debug like
  previews - the 404 status itself stays (extension uses it for failure
  detection), only the log level is lowered

tests/routes/test_download_queue_handlers.py

@@ -0,0 +1,186 @@
+"""Handler-level tests for download queue terminal/status transitions.
+
+Regression test: a "not found in queue" outcome must be returned as HTTP 200
+with ``success: false``, not 404. The browser extension's apiFetch treats any
+404 as a missing endpoint and retries a legacy URL, producing spurious
+``/api/downloads/queue/complete ... 404`` warnings on every completion.
+"""
+
+import json
+import logging
+from pathlib import Path
+
+import pytest
+from aiohttp import web
+from aiohttp.test_utils import make_mocked_request
+
+from py.routes.handlers.model_handlers import ModelDownloadHandler
+from py.services.download_queue_service import DownloadQueueService
+
+
+def _make_handler() -> ModelDownloadHandler:
+    return ModelDownloadHandler(
+        ws_manager=None,  # pyright: ignore[reportArgumentType] - unused by queue endpoints
+        logger=logging.getLogger("test-download-queue"),
+        download_use_case=None,  # pyright: ignore[reportArgumentType] - unused by queue endpoints
+        download_coordinator=None,  # pyright: ignore[reportArgumentType] - unused by queue endpoints
+    )
+
+
+def _queue_request(path: str, query: dict[str, str]) -> web.Request:
+    query_string = "&".join(f"{key}={value}" for key, value in query.items())
+    return make_mocked_request("GET", f"{path}?{query_string}")
+
+
+@pytest.fixture
+def queue_service(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> DownloadQueueService:
+    """Return a tmp-backed DownloadQueueService and stub the singleton."""
+    service = DownloadQueueService(db_path=str(tmp_path / "queue.sqlite"))
+
+    async def fake_get_instance(_cls: object = None) -> DownloadQueueService:
+        return service
+
+    monkeypatch.setattr(DownloadQueueService, "get_instance", fake_get_instance)
+    return service
+
+
+@pytest.mark.asyncio
+async def test_complete_missing_download_returns_200_not_404(
+    queue_service: DownloadQueueService,
+) -> None:
+    """Completing a download that is not queued is a business outcome."""
+    handler = _make_handler()
+    response = await handler.complete_download_in_queue(
+        _queue_request(
+            "/api/lm/downloads/queue/complete",
+            {"download_id": "dl-nope", "status": "completed"},
+        )
+    )
+    assert response.status == 200
+    text = response.text
+    assert text is not None
+    assert json.loads(text) == {
+        "success": False,
+        "error": "Download not found in queue",
+    }
+    # The failed completion must not have side effects on the queue.
+    assert await queue_service.get_queue() == []
+
+
+@pytest.mark.asyncio
+async def test_complete_queued_download_returns_success(
+    queue_service: DownloadQueueService,
+) -> None:
+    """The happy path still moves the item to history with HTTP 200."""
+    await queue_service.add_to_queue(download_id="dl-1", model_id=1)
+    handler = _make_handler()
+    response = await handler.complete_download_in_queue(
+        _queue_request(
+            "/api/lm/downloads/queue/complete",
+            {"download_id": "dl-1", "status": "completed"},
+        )
+    )
+    assert response.status == 200
+    text = response.text
+    assert text is not None
+    payload = json.loads(text)
+    assert payload["success"] is True
+    # The returned item reflects the pre-transition queue record; the
+    # terminal status lands in history.
+    history = await queue_service.get_history()
+    assert len(history["items"]) == 1
+    assert history["items"][0]["status"] == "completed"
+
+
+@pytest.mark.asyncio
+async def test_status_missing_download_returns_200_not_404(
+    queue_service: DownloadQueueService,
+) -> None:
+    """Status updates for unknown items also return 200 with success: false."""
+    handler = _make_handler()
+    response = await handler.update_download_queue_status(
+        _queue_request(
+            "/api/lm/downloads/queue/status",
+            {"download_id": "dl-nope", "status": "downloading"},
+        )
+    )
+    assert response.status == 200
+    text = response.text
+    assert text is not None
+    assert json.loads(text) == {
+        "success": False,
+        "error": "Download not found in queue",
+    }
+    assert await queue_service.get_queue() == []
+
+
+@pytest.mark.asyncio
+async def test_status_queued_download_returns_success(
+    queue_service: DownloadQueueService,
+) -> None:
+    """The happy path still updates the queue item with HTTP 200."""
+    await queue_service.add_to_queue(download_id="dl-2", model_id=2)
+    handler = _make_handler()
+    response = await handler.update_download_queue_status(
+        _queue_request(
+            "/api/lm/downloads/queue/status",
+            {"download_id": "dl-2", "status": "downloading"},
+        )
+    )
+    assert response.status == 200
+    text = response.text
+    assert text is not None
+    assert json.loads(text) == {"success": True}
+
+
+@pytest.mark.asyncio
+async def test_retry_missing_history_returns_200_not_404(
+    queue_service: DownloadQueueService,
+) -> None:
+    """Retrying a history entry that no longer exists is a business outcome."""
+    handler = _make_handler()
+    response = await handler.retry_download_from_history(
+        _queue_request(
+            "/api/lm/downloads/history/retry",
+            {"download_id": "dl-nope"},
+        )
+    )
+    assert response.status == 200
+    text = response.text
+    assert text is not None
+    assert json.loads(text) == {
+        "success": False,
+        "error": "History item not found or not retryable",
+    }
+    # No side effects: history and queue stay empty.
+    history = await queue_service.get_history()
+    assert history["items"] == []
+    assert await queue_service.get_queue() == []
+
+
+@pytest.mark.asyncio
+async def test_retry_failed_history_returns_success(
+    queue_service: DownloadQueueService,
+) -> None:
+    """The happy path still re-queues a retryable history entry with HTTP 200."""
+    await queue_service.add_to_history(
+        download_id="dl-fail", model_id=1, status="failed"
+    )
+    handler = _make_handler()
+    response = await handler.retry_download_from_history(
+        _queue_request(
+            "/api/lm/downloads/history/retry",
+            {"download_id": "dl-fail"},
+        )
+    )
+    assert response.status == 200
+    text = response.text
+    assert text is not None
+    payload = json.loads(text)
+    assert payload["success"] is True
+    # The retried item is re-queued under a fresh download_id.
+    queue = await queue_service.get_queue()
+    assert len(queue) == 1
+    assert queue[0]["status"] == "queued"