feat(eval): add custom system prompt support for step-1 classification

services/batch-agent/app/agent_runner.py

@@ -400,6 +400,7 @@ async def _classify_file(
     projects: list[dict],
     config_data_types: list[str],
     langfuse_handler: Any | None = None,
+    custom_system_prompt: str | None = None,
 ) -> tuple[str, list[str], str | None]:
     fallback: tuple[str, list[str], str | None] = ("new", list(config_data_types), None)
 
@@ -421,14 +422,20 @@ async def _classify_file(
         if d in _DOMAIN_DESCRIPTIONS
     )
 
-    system = tracing.compile_prompt(
-        "batch_file_classifier",
-        fallback=_STEP1_SYSTEM_PROMPT,
-        variables={
-            "domain_definitions": domain_definitions,
-            "projects_list": projects_list,
-        },
-    )
+    if custom_system_prompt:
+        # Fixture-provided prompt takes absolute priority
+        system = custom_system_prompt.format_map(
+            {"domain_definitions": domain_definitions, "projects_list": projects_list}
+        )
+    else:
+        system = tracing.compile_prompt(
+            "batch_file_classifier",
+            fallback=_STEP1_SYSTEM_PROMPT,
+            variables={
+                "domain_definitions": domain_definitions,
+                "projects_list": projects_list,
+            },
+        )
 
     llm = get_llm(callbacks=[langfuse_handler] if langfuse_handler else None)
     try: