Document local mine repository authority

ober

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+## STOP: Local Mine Repositories Are Authoritative
+
+Always commit development changes only in the matching `/Users/user/mine/jerboa-*` repository. Never commit development changes in `vendor/jerboa-*`; vendor checkouts are read-only mirrors for reference and dependency inspection only.
+
+Before starting work that compares against or uses a vendor checkout, update that vendor checkout to the latest revision and verify it matches exactly with the corresponding `/Users/user/mine/jerboa-*` repository state. If they differ, stop and sync from `/Users/user/mine/jerboa-*` before making or committing changes. The `/Users/user/mine/jerboa-*` worktree must always represent the latest authoritative version.
+
 ## STOP: Editing `.ss`/`.sls` Files — Mandatory Rules
 
 These rules exist because local-model sessions have lost **hours** fighting