feat(llm): enhance LiteLLMCaller to support custom API key handling a…

backend/modules/llm/litellm_caller.py

@@ -27,7 +27,14 @@
 
 
 class LiteLLMCaller:
-    """Clean interface for all LLM calling patterns using LiteLLM."""
+    """Clean interface for all LLM calling patterns using LiteLLM.
+
+    Note: this class may set provider-specific LLM API key environment
+    variables (for example ``OPENAI_API_KEY``) to maintain compatibility
+    with LiteLLM's internal provider detection. These mutations are
+    best-effort only and are not intended to provide strong isolation
+    guarantees in multi-tenant or highly concurrent environments.
+    """
 
     def __init__(self, llm_config=None, debug_mode: bool = False):
         """Initialize with optional config dependency injection."""
@@ -85,20 +92,40 @@ def _get_model_kwargs(self, model_name: str, temperature: Optional[float] = None
         except ValueError as e:
             logger.error(f"Failed to resolve API key for model {model_name}: {e}")
             raise
-        
+
         if api_key:
+            # Always pass api_key to LiteLLM for all providers
+            kwargs["api_key"] = api_key
+
+            # Additionally set provider-specific env vars for LiteLLM's internal logic
+            def _set_env_var_if_needed(env_key: str, value: str) -> None:
+                existing = os.environ.get(env_key)
+                if existing is None:
+                    os.environ[env_key] = value
+                elif existing != value:
+                    logger.warning(
+                        "Overwriting existing environment variable %s for model %s", 
+                        env_key,
+                        model_name,
+                    )
+                    os.environ[env_key] = value
+
             if "openrouter" in model_config.model_url:
-                kwargs["api_key"] = api_key
-                # LiteLLM will automatically set the correct env var
-                os.environ["OPENROUTER_API_KEY"] = api_key
+                _set_env_var_if_needed("OPENROUTER_API_KEY", api_key)
             elif "openai" in model_config.model_url:
-                os.environ["OPENAI_API_KEY"] = api_key
+                _set_env_var_if_needed("OPENAI_API_KEY", api_key)
             elif "anthropic" in model_config.model_url:
-                os.environ["ANTHROPIC_API_KEY"] = api_key
+                _set_env_var_if_needed("ANTHROPIC_API_KEY", api_key)
             elif "google" in model_config.model_url:
-                os.environ["GOOGLE_API_KEY"] = api_key
+                _set_env_var_if_needed("GOOGLE_API_KEY", api_key)
             elif "cerebras" in model_config.model_url:
-                os.environ["CEREBRAS_API_KEY"] = api_key
+                _set_env_var_if_needed("CEREBRAS_API_KEY", api_key)
+            else:
+                # Custom endpoint - set OPENAI_API_KEY as fallback for
+                # OpenAI-compatible endpoints. This is a heuristic and
+                # only updates the env var if it is unset or already
+                # matches the same value.
+                _set_env_var_if_needed("OPENAI_API_KEY", api_key)
 
         # Set custom API base for non-standard endpoints
         if hasattr(model_config, 'model_url') and model_config.model_url: