markdown-format + rate-limit-guard: hook-utils.sh is byte-identical in both plugins — needs a shared-source seam

[kyle-sexton]

plugins/markdown-format/hooks/hook-utils.sh and plugins/rate-limit-guard/hooks/hook-utils.sh are byte-identical (1657 lines, 0-line diff, verified 2026-08-08). A fix to one will not propagate to the other. Plugin-form isolation forbids cross-plugin reach-outs at runtime, so the seam is likely build/sync-time (generate both from one source, or a drift-check test that fails when they diverge).

From the prompting-guide alignment audit (PR #2018, small-group lane observation).

[kyle-sexton]

Already covered — this is the designed seam, not a gap. lib/hook-utils.sh is the canonical source; scripts/sync-hook-utils.sh copies it into every carrying plugin (a plugin opts in by committing an initial copy at plugins/<name>/hooks/hook-utils.sh), and CI's required hook-utils-sync check runs sync-hook-utils.sh --check on every PR, failing on any divergence, plus --check-bump semantics so a lib change without a plugin version bump cannot ship silently. The audit lane observed the byte-identical copies without finding the sync script; no change needed.