fix(mistralai): detect v0.x package + force pip --upgrade in Dockerfile

The container had mistralai v0.x installed (identified by '(unknown location)'
in the traceback and ImportError on 'Mistral'). Two fixes:

1. provider_mistral.py: detect v0.x vs not-installed with separate
RuntimeError messages that point clearly to the Docker rebuild:
- v0.x present → "mistralai 0.x ne supporte pas la vision, reconstruisez"
- not installed → "mistralai n'est pas installé, reconstruisez"
Raises RuntimeError (job fails cleanly) instead of ImportError.

2. infra/Dockerfile: add --upgrade to pip install so Docker rebuilds
always upgrade to the latest compatible version rather than keeping
a stale cached layer that had mistralai 0.x.

Added test: test_generate_content_v0_package_raises_runtime_error.
Note: vertex_api_key 403 in logs is a GCP configuration issue (Generative
Language API not enabled in project 347387665578) — not a code fix.

https://claude.ai/code/session_018woyEHc8HG2th7V4ewJ4Kg

backend/app/services/ai/provider_mistral.py

@@ -69,11 +69,23 @@ class MistralProvider(AIProvider):
 
         try:
             from mistralai import Mistral  # v1.x — import local
-        except ImportError as exc:
-            raise ImportError(
-                "Impossible d'importer 'Mistral' depuis mistralai. "
-                "Vérifiez que le package est installé : pip install 'mistralai>=1.0'"
-            ) from exc
+        except ImportError:
+            # Détecter si c'est mistralai v0.x (ne supporte pas la vision / Pixtral)
+            try:
+                import mistralai as _ms_pkg  # noqa: F401
+                _v0_present = True
+            except ImportError:
+                _v0_present = False
+            if _v0_present:
+                raise RuntimeError(
+                    "Le package mistralai est installé en version 0.x qui ne supporte pas "
+                    "la vision (Pixtral). Reconstruisez le container Docker pour obtenir "
+                    "mistralai>=1.0 : `docker build --no-cache ...`"
+                )
+            raise RuntimeError(
+                "Le package mistralai n'est pas installé. "
+                "Ajoutez 'mistralai>=1.0' aux dépendances et reconstruisez le container."
+            )
 
         api_key = os.environ[_ENV_KEY]
         client = Mistral(api_key=api_key)

backend/tests/test_provider_mistral.py

@@ -164,3 +164,19 @@ def test_generate_content_empty_response(monkeypatch):
 
     result = MistralProvider().generate_content(b"img", "prompt", "pixtral-large-latest")
     assert result == ""
+
+
+def test_generate_content_v0_package_raises_runtime_error(monkeypatch):
+    """Si mistralai est installé en v0.x (pas de classe Mistral), lève RuntimeError avec un message clair."""
+    monkeypatch.setenv("MISTRAL_API_KEY", "test-key")
+
+    import sys
+    import types as _types
+
+    # Simuler mistralai v0.x : le module existe mais n'a pas la classe Mistral
+    fake_mistralai_v0 = _types.ModuleType("mistralai")
+    # Pas d'attribut Mistral → from mistralai import Mistral lèvera ImportError
+    monkeypatch.setitem(sys.modules, "mistralai", fake_mistralai_v0)
+
+    with pytest.raises(RuntimeError, match="version 0.x"):
+        MistralProvider().generate_content(b"img", "prompt", "pixtral-large-latest")

infra/Dockerfile

@@ -35,7 +35,7 @@ WORKDIR /app
 COPY backend/pyproject.toml /tmp/build/
 RUN mkdir -p /tmp/build/app \
     && touch /tmp/build/app/__init__.py \
-    && pip install --no-cache-dir /tmp/build/ \
+    && pip install --no-cache-dir --upgrade /tmp/build/ \
     && rm -rf /tmp/build
 
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