fix(prompt): place scratchpad under session folder

dana/core/agent/star_agent.py

@@ -304,16 +304,23 @@ def set_session_id(self, session_id: str, reload_timeline: bool = False) -> None
         if not reload_timeline:
             # Pure relabel — caller owns the timeline; do not flush/rebuild.
             self._session_id = session_id
+            self._invalidate_system_prompt_cache()
             return
 
         timeline = getattr(self, "_timeline", None)
         if timeline is not None and getattr(timeline, "_repository", None) is not None and timeline.timeline:
             timeline.save(self._session_id)
 
         self._session_id = session_id
+        self._invalidate_system_prompt_cache()
         self._timeline = self._build_timeline()
         self._timeline.rehydrate()
 
+    def _invalidate_system_prompt_cache(self) -> None:
+        runtime = getattr(self, "_runtime", None)
+        if runtime is not None and hasattr(runtime, "invalidate_system_prompt_cache"):
+            runtime.invalidate_system_prompt_cache()
+
     def resume(self, session_id: str) -> None:
         """Resume a persisted session by id, reloading its timeline from disk.
 

dana/core/prompt/environment_info.py

@@ -98,13 +98,19 @@ def git_recent_commits(self) -> str:
 
     @property
     def scratchpad_directory(self) -> str:
-        # Deferred to avoid circular import at module level
+        from dana.core.agent.tool_result_dump import resolve_session_folder_for_agent
+
+        session_folder = resolve_session_folder_for_agent(self._agent)
+        if session_folder is not None:
+            tmp_path = session_folder / "scratchpad"
+            tmp_path.mkdir(parents=True, exist_ok=True)
+            return str(tmp_path.absolute())
+
+        # Deferred to avoid circular import at module level.
         from dana.config.storage_config import FileStorageConfig
 
         workspace_folder = Path(FileStorageConfig().workspace_folder)
-
-        relative_prompt_path = Path(self._relative_path)
         _session_id = getattr(self._agent, "_session_id", str(uuid4()))
-        tmp_path = workspace_folder / relative_prompt_path.parent / "tmp" / _session_id / "scratchpad"
+        tmp_path = workspace_folder / str(self._agent.object_id) / "sessions" / _session_id / "scratchpad"
         tmp_path.mkdir(parents=True, exist_ok=True)
         return str(tmp_path.absolute())

dana/core/runtime/codec/codec_base.py

@@ -98,6 +98,10 @@ def _build_system_prompt(self, agent: STARAgent) -> str:
         prompt_api = self._get_prompt_api(agent)
         return prompt_api.system_prompt
 
+    def invalidate_system_prompt_cache(self) -> None:
+        if self._prompt_api is not None:
+            self._prompt_api._system_prompt = None
+
     def call_llm(
         self,
         messages: list[LLMMessage],

tests/unit/core/star/test_set_session_id.py

@@ -8,11 +8,14 @@
 from __future__ import annotations
 
 from datetime import datetime
+from pathlib import Path
+from unittest.mock import Mock
 
 import pytest
 
 from dana.config.storage_config import FileStorageConfig
 from dana.core.agent.star_agent import STARAgent
+from dana.core.prompt.environment_info import EnvironmentInfo
 from dana.core.timeline.compressed_timeline import CompressedTimeline
 from dana.core.timeline.timeline import TimelineEntry, TimelineEntryType
 from dana.repositories.local_file_repository import LocalTimelineRepository
@@ -146,6 +149,42 @@ def test_same_session_id_is_fast_path(self, tmp_path):
         assert agent._timeline is original_timeline
         assert [e.content for e in agent._timeline.timeline] == ["untouched"]
 
+    def test_session_scratchpad_lives_under_session_folder(self, tmp_path):
+        agent = _make_agent(tmp_path, session_id="A")
+
+        scratchpad = Path(EnvironmentInfo(agent, "NativeToolsCodec/agent-1/prompts").scratchpad_directory)
+
+        assert scratchpad == tmp_path / "agent-1" / "sessions" / "A" / "scratchpad"
+        assert scratchpad.is_dir()
+
+    def test_relabel_invalidates_system_prompt_cache(self, tmp_path):
+        agent = _make_agent(tmp_path, session_id="A")
+        agent._runtime.invalidate_system_prompt_cache = Mock()
+
+        agent.set_session_id("B", reload_timeline=False)
+
+        agent._runtime.invalidate_system_prompt_cache.assert_called_once_with()
+
+    def test_reload_invalidates_system_prompt_cache(self, tmp_path):
+        agent = _make_agent(tmp_path, session_id="A")
+        agent._runtime.invalidate_system_prompt_cache = Mock()
+
+        agent.set_session_id("B", reload_timeline=True)
+
+        agent._runtime.invalidate_system_prompt_cache.assert_called_once_with()
+
+    def test_cached_system_prompt_rerenders_after_session_change(self, tmp_path):
+        agent = _make_agent(tmp_path, session_id="A")
+        prompt_api = agent._runtime._get_prompt_api(agent)
+        prompt_api.load = lambda: "scratch={{scratchpad_directory}}"
+
+        first_prompt = agent._runtime._build_system_prompt(agent)
+        agent.set_session_id("B", reload_timeline=False)
+        second_prompt = agent._runtime._build_system_prompt(agent)
+
+        assert str(tmp_path / "agent-1" / "sessions" / "A" / "scratchpad") in first_prompt
+        assert str(tmp_path / "agent-1" / "sessions" / "B" / "scratchpad") in second_prompt
+
 
 class TestRehydrate:
     """CompressedTimeline.rehydrate guards."""