fix: tighten memory and session recall guidance

Remove diary-style memory framing from the system prompt and memory tool
schema, explicitly steer task/session logs to session_search, and clarify
that session_search is for cross-session recall after checking the current
conversation first. Add regression tests for the updated guidance text.

tests/agent/test_prompt_builder.py

@@ -15,10 +15,30 @@ from agent.prompt_builder import (
     build_context_files_prompt,
     CONTEXT_FILE_MAX_CHARS,
     DEFAULT_AGENT_IDENTITY,
+    MEMORY_GUIDANCE,
+    SESSION_SEARCH_GUIDANCE,
     PLATFORM_HINTS,
 )
 
 
+# =========================================================================
+# Guidance constants
+# =========================================================================
+
+
+class TestGuidanceConstants:
+    def test_memory_guidance_discourages_task_logs(self):
+        assert "durable facts" in MEMORY_GUIDANCE
+        assert "Do NOT save task progress" in MEMORY_GUIDANCE
+        assert "session_search" in MEMORY_GUIDANCE
+        assert "like a diary" not in MEMORY_GUIDANCE
+        assert ">80%" not in MEMORY_GUIDANCE
+
+    def test_session_search_guidance_is_simple_cross_session_recall(self):
+        assert "relevant cross-session context exists" in SESSION_SEARCH_GUIDANCE
+        assert "recent turns of the current session" not in SESSION_SEARCH_GUIDANCE
+
+
 # =========================================================================
 # Context injection scanning
 # =========================================================================

tests/tools/test_memory_tool.py

@@ -9,9 +9,24 @@ from tools.memory_tool import (
     memory_tool,
     _scan_memory_content,
     ENTRY_DELIMITER,
+    MEMORY_SCHEMA,
 )
 
 
+# =========================================================================
+# Tool schema guidance
+# =========================================================================
+
+class TestMemorySchema:
+    def test_discourages_diary_style_task_logs(self):
+        description = MEMORY_SCHEMA["description"]
+        assert "Do NOT save task progress" in description
+        assert "session_search" in description
+        assert "like a diary" not in description
+        assert "temporary task state" in description
+        assert ">80%" not in description
+
+
 # =========================================================================
 # Security scanning
 # =========================================================================

tests/tools/test_session_search.py

@@ -9,9 +9,21 @@ from tools.session_search_tool import (
     _format_conversation,
     _truncate_around_matches,
     MAX_SESSION_CHARS,
+    SESSION_SEARCH_SCHEMA,
 )
 
 
+# =========================================================================
+# Tool schema guidance
+# =========================================================================
+
+class TestSessionSearchSchema:
+    def test_keeps_cross_session_recall_guidance_without_current_session_nudge(self):
+        description = SESSION_SEARCH_SCHEMA["description"]
+        assert "past conversations" in description
+        assert "recent turns of the current session" not in description
+
+
 # =========================================================================
 # _format_timestamp
 # =========================================================================