Session Handoff

Preserve session context per topic. Each topic gets one handoff file holding its current resumption state (not a diary). A single index is the log and the menu of what can be picked up.

Layout

handoffs/
├── INDEX.md            # active-topics table + reverse-chron session log
├── <topic-slug>.md     # one file per topic, rewritten each session end
└── archive/            # completed topics