Development record

.abcd/development/brief/04-surfaces/01-ahoy.md:1473-1475 calls uninstall then install a tested round-trip invariant: zero actionable gaps, and state byte-identical to a fresh install save for the setup date. `TestUninstallInstallRoundTrip` (internal/core/ahoy/idempotency_test.go:179) checks only that the marker block is gone, `.abcd/config.json` survives and the re-install status is clean. It compares no bytes and asks for no gap count.