fix(vision): worker down o in timeout non esce più come 500 nudo (#14)

_call_worker distingue httpx.TimeoutException (504) dal resto dei
TransportError/HTTPError (502, RemoteProtocolError incluso). Un 422 del
worker si propaga come 422 con il motivo del worker, non più 502 generico.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/backend/tests/test_vision_worker_transport.py

@@ -115,3 +115,75 @@ async def test_a_well_formed_response_still_passes_through(monkeypatch):
     report = await _call_worker(b"img", {"schema_version": 1, "tools": []})
 
     assert report == body
+
+
+# ---------------------------------------------------------------------------
+# #14: the worker dying mid-response (RemoteProtocolError) or a connect
+# timeout (ConnectTimeout, an httpx.TimeoutException) used to fall through
+# every except clause here and surface as a naked 500.
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_the_worker_dying_mid_response_answers_502_not_a_naked_500(monkeypatch):
+    _install(
+        monkeypatch,
+        raises=httpx.RemoteProtocolError(
+            "Server disconnected without sending a response."
+        ),
+    )
+
+    with pytest.raises(HTTPException) as excinfo:
+        await _call_worker(b"img", {"schema_version": 1, "tools": []})
+
+    assert excinfo.value.status_code == 502
+    assert "unreachable" in excinfo.value.detail.lower()
+
+
+@pytest.mark.asyncio
+async def test_a_connect_timeout_answers_504(monkeypatch):
+    """ConnectTimeout is an httpx.TimeoutException, not caught by name before -
+    only httpx.ReadTimeout was."""
+    _install(monkeypatch, raises=httpx.ConnectTimeout("connect timed out"))
+
+    with pytest.raises(HTTPException) as excinfo:
+        await _call_worker(b"img", {"schema_version": 1, "tools": []})
+
+    assert excinfo.value.status_code == 504
+    assert "time" in excinfo.value.detail.lower()
+
+
+# ---------------------------------------------------------------------------
+# #15: a 422 from the worker (bad image, malformed graph) must reach the
+# Maker as a 422 with the worker's own reason, not a flattened 502.
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_a_422_from_the_worker_propagates_as_422_with_its_detail(monkeypatch):
+    _install(
+        monkeypatch,
+        response=_FakeResponse(
+            422, body={"detail": "image is not decodable: cannot identify image file"},
+        ),
+    )
+
+    with pytest.raises(HTTPException) as excinfo:
+        await _call_worker(b"img", {"schema_version": 1, "tools": []})
+
+    assert excinfo.value.status_code == 422
+    assert "not decodable" in excinfo.value.detail
+
+
+@pytest.mark.asyncio
+async def test_a_422_from_the_worker_without_json_body_still_propagates(monkeypatch):
+    _install(
+        monkeypatch,
+        response=_FakeResponse(422, text="plain text reason", raise_on_json=True),
+    )
+
+    with pytest.raises(HTTPException) as excinfo:
+        await _call_worker(b"img", {"schema_version": 1, "tools": []})
+
+    assert excinfo.value.status_code == 422
+    assert excinfo.value.detail == "plain text reason"