vision: anteprima DXF nel worker e nel backend (Refs #101)

Worker: POST /dxf/preview legge il DXF con read_xld_dxf (lo stesso lettore di
CompareDxf) e ritorna contorni in mm con y verso il basso, bbox, dimensioni,
entita e punti (tetto 20000, decimazione uniforme). Backend: POST
/api/vision/dxf-preview (Maker) che inoltra al worker; 422 inoltrato.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/backend/tests/test_vision_dxf_preview.py

@@ -0,0 +1,90 @@
+"""#101: POST /api/vision/dxf-preview, anteprima del DXF nel wizard.
+
+Il worker non gira nei test: `vision_service.dxf_preview` si sostituisce.
+"""
+import pytest
+from fastapi import HTTPException
+
+from src.backend.config import settings
+from src.backend.services import vision_service
+from src.backend.tests.conftest import auth_headers
+
+BODY = {
+    "contorni": [[[0.0, 0.0], [10.0, 0.0], [10.0, 5.0], [0.0, 5.0], [0.0, 0.0]]],
+    "bbox": {"xmin": 0.0, "ymin": 0.0, "xmax": 10.0, "ymax": 5.0},
+    "larghezza_mm": 10.0, "altezza_mm": 5.0, "entita": 1, "punti": 5,
+}
+
+
+def _post(client, user, content=b"0\nEOF"):
+    return client.post(
+        "/api/vision/dxf-preview",
+        headers=auth_headers(user),
+        files={"dxf": ("d.dxf", content, "application/octet-stream")},
+    )
+
+
+@pytest.mark.asyncio
+async def test_dxf_preview_forwards_the_file_and_returns_the_worker_body(
+    client, maker_user, monkeypatch,
+):
+    calls = []
+
+    async def fake(dxf_bytes, worker_url=None):
+        calls.append(dxf_bytes)
+        return BODY
+
+    monkeypatch.setattr("src.backend.services.vision_service.dxf_preview", fake)
+    resp = await _post(client, maker_user, b"DXF-BYTES")
+    assert resp.status_code == 200, resp.text
+    assert resp.json() == BODY
+    assert calls == [b"DXF-BYTES"]
+
+
+@pytest.mark.asyncio
+async def test_dxf_preview_forwards_the_worker_422(client, maker_user, monkeypatch):
+    async def fake(dxf_bytes, worker_url=None):
+        raise HTTPException(status_code=422, detail="DXF illeggibile: file vuoto")
+
+    monkeypatch.setattr("src.backend.services.vision_service.dxf_preview", fake)
+    resp = await _post(client, maker_user, b"")
+    assert resp.status_code == 422
+    assert resp.json()["detail"] == "DXF illeggibile: file vuoto"
+
+
+@pytest.mark.asyncio
+async def test_dxf_preview_requires_maker(client, measurement_tec_user, monkeypatch):
+    async def fake(dxf_bytes, worker_url=None):
+        return BODY
+
+    monkeypatch.setattr("src.backend.services.vision_service.dxf_preview", fake)
+    resp = await _post(client, measurement_tec_user)
+    assert resp.status_code == 403
+
+
+@pytest.mark.asyncio
+async def test_dxf_preview_too_big_is_422(client, maker_user, monkeypatch):
+    monkeypatch.setattr(settings, "max_upload_size_mb", 0)
+    resp = await _post(client, maker_user, b"x" * 10)
+    assert resp.status_code == 422
+
+
+@pytest.mark.asyncio
+async def test_dxf_preview_service_posts_to_worker_and_checks_shape(monkeypatch):
+    seen = {}
+
+    async def fake_multipart(path, *, files, data, worker_url=None, timeout=120.0):
+        seen.update(path=path, files=files)
+        return BODY
+
+    monkeypatch.setattr(vision_service, "call_worker_multipart", fake_multipart)
+    assert await vision_service.dxf_preview(b"abc") == BODY
+    assert seen["path"] == "/dxf/preview" and seen["files"]["dxf"][1] == b"abc"
+
+    async def malformed(path, *, files, data, worker_url=None, timeout=120.0):
+        return {"contorni": []}
+
+    monkeypatch.setattr(vision_service, "call_worker_multipart", malformed)
+    with pytest.raises(HTTPException) as exc:
+        await vision_service.dxf_preview(b"abc")
+    assert exc.value.status_code == 502