prompt template file resolution ordering

src/fast_agent/core/fastagent.py

@@ -865,6 +865,15 @@ def _apply_instruction_context(
             if request_params is not None:
                 request_params.systemPrompt = resolved
 
+            # TODO -- find a cleaner way of doing this
+            # Keep any attached LLM in sync so the provider sees the resolved prompt
+            llm = getattr(agent, "_llm", None)
+            if llm is not None:
+                if getattr(llm, "default_request_params", None) is not None:
+                    llm.default_request_params.systemPrompt = resolved
+                if hasattr(llm, "instruction"):
+                    llm.instruction = resolved
+
     def _apply_skills_to_agent_configs(self, default_skills: list[SkillManifest]) -> None:
         self._default_skill_manifests = list(default_skills)
 

tests/integration/instruction_templates/FOO.md

@@ -0,0 +1 @@
+This text came from FOO.md and should replace the placeholder.

tests/integration/instruction_templates/fastagent.config.yaml

@@ -0,0 +1,7 @@
+default_model: passthrough
+
+logger:
+  level: "error"
+  progress_display: false
+  show_chat: false
+  show_tools: false

tests/integration/instruction_templates/test_file_silent_instruction.py

@@ -0,0 +1,38 @@
+from pathlib import Path
+
+import pytest
+
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_file_silent_reaches_llm_request_params(fast_agent):
+    """Ensure {{file_silent:...}} is resolved before the LLM sees the system prompt."""
+    fast = fast_agent
+    file_text = Path("FOO.md").read_text(encoding="utf-8").strip()
+
+    @fast.agent(
+        name="file_template_agent",
+        instruction="System prompt start. {{file_silent:FOO.md}}",
+        model="passthrough",
+    )
+    async def agent_function():
+        async with fast.run() as agent_app:
+            agent = agent_app.file_template_agent
+
+            # Agent-facing instruction should have the file contents applied
+            assert "{{file_silent:FOO.md}}" not in agent.instruction
+            assert file_text in agent.instruction
+
+            # The LLM request params (what the provider sees) should also be resolved
+            request_params = agent.llm.get_request_params()
+            assert request_params.systemPrompt is not None
+            assert "{{file_silent:FOO.md}}" not in request_params.systemPrompt
+            assert file_text in request_params.systemPrompt
+
+            # Default params should stay in sync for future calls
+            assert file_text in agent.llm.default_request_params.systemPrompt
+
+            response = await agent.send("ping")
+            assert "ping" in response
+
+    await agent_function()