ROADMAP.md was named as a destination in two places but never created,
indexed, or read back. Add the convention to how-i-work.md, note it after
the README decision tree and in the loads-when table, give it a row in the
portability layer table, make the retrofit prompt create it, and have
handoff seed it and pull from it when Current state's next steps run thin.
Automate the per-project retrofit (git audit, verify, scope, commit,
validate) as a main-thread slash command that asks for the judgment
calls. Step 1 (mining a past chat) stays manual — the command surfaces
which conversation to mine and hands back, since it can't resume one.