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.

tools/session_search_tool.py

@@ -341,8 +341,8 @@ SESSION_SEARCH_SCHEMA = {
         "- The user references a project, person, or concept that seems familiar but isn't in memory\n"
         "- You want to check if you've solved a similar problem before\n"
         "- The user asks 'what did we do about X?' or 'how did we fix Y?'\n\n"
-        "Don't hesitate to search -- it's fast and cheap. Better to search and confirm "
-        "than to guess or ask the user to repeat themselves.\n\n"
+        "Don't hesitate to search when it is actually cross-session -- it's fast and cheap. "
+        "Better to search and confirm than to guess or ask the user to repeat themselves.\n\n"
         "Search syntax: keywords joined with OR for broad recall (elevenlabs OR baseten OR funding), "
         "phrases for exact match (\"docker networking\"), boolean (python NOT java), prefix (deploy*). "
         "IMPORTANT: Use OR between keywords for best results — FTS5 defaults to AND which misses "