save_memory vs update_context_file - when to use each

Think of it as: save_memory is a sticky note, update_context_file is editing the manual.

• save_memory: behavioral preferences, one-off facts about a specific customer, 'this user hates when we use exclamation marks'. Retrieved by semantic match on future sessions for the same customer / tenant
• update_context_file: durable procedural knowledge. 'The fix for error E-402 is to run migration_042'. Written into a KB file, versioned, auditable, and picked up by RAG for any future session that hits the same topic

Rule of thumb: if the knowledge applies to anyone who hits this issue in the future, it's update_context_file. If it's specifically about one customer's preferences or a one-time situation, it's save_memory.