feat(middleware): scope model fallback to provider/network errors only

surfsense_backend/app/agents/new_chat/chat_deepagent.py

@@ -31,7 +31,6 @@ from langchain.agents import create_agent
 from langchain.agents.middleware import (
     LLMToolSelectorMiddleware,
     ModelCallLimitMiddleware,
-    ModelFallbackMiddleware,
     TodoListMiddleware,
     ToolCallLimitMiddleware,
 )
@@ -77,6 +76,9 @@ from app.agents.new_chat.middleware import (
     create_surfsense_compaction_middleware,
     default_skills_sources,
 )
+from app.agents.new_chat.middleware.scoped_model_fallback import (
+    ScopedModelFallbackMiddleware,
+)
 from app.agents.new_chat.permissions import Rule, Ruleset
 from app.agents.new_chat.plugin_loader import (
     PluginContext,
@@ -792,15 +794,15 @@ def _build_compiled_agent_blocking(
     # Fallback chain — primary is the agent's own model; we add cheap
     # alternatives. Off by default; only the first call site that
     # configures the chain via env should enable it.
-    fallback_mw: ModelFallbackMiddleware | None = None
+    fallback_mw: ScopedModelFallbackMiddleware | None = None
     if flags.enable_model_fallback and not flags.disable_new_agent_stack:
         try:
-            fallback_mw = ModelFallbackMiddleware(
+            fallback_mw = ScopedModelFallbackMiddleware(
                 "openai:gpt-4o-mini",
                 "anthropic:claude-3-5-haiku-20241022",
             )
         except Exception:
-            logging.warning("ModelFallbackMiddleware init failed; skipping.")
+            logging.warning("ScopedModelFallbackMiddleware init failed; skipping.")
             fallback_mw = None
     model_call_limit_mw = (
         ModelCallLimitMiddleware(