[tbhb-agent]

Summary

Run commit-message previews through agentrepo commit-preview. Keep the existing helper as a capability probe with a frozen shell fallback for N-2 consumers.

Why

Move preview orchestration into Go while preserving sign-off selection, draft bytes, and the actual commit-msg gate interface. Consumers with older binaries still need the shell path.

Verification

AC	Command	Result
AC1	mise run test	Passed on Linux: frozen-shell parity checks draft bytes on success and failure.
AC2	mise run test	Passed on Linux: checks preserve the existing sign-off and trailer order.
AC3	mise run test	Passed on Linux: checks verify identity precedence and empty settings across worktrees.
AC4	mise run test	Passed on Linux: refused identities stop gate execution.
AC5	mise run test	Passed on Linux: invalid identity policy stops gate execution.
AC6	mise run test and bats tests/devtools/lint-commit-msg.bats	Passed on Linux: the gate stub validates arguments and the temporary COMMIT_EDITMSG basename. Retained checks exercise gate results and the real hook with body-width and commit-scope Vale checks.
AC7	mise run test	Passed on Linux: checks verify temporary preview cleanup after success and failure.
AC8	mise run test	Passed on Linux: repository behavior settings can't supply a sign-off.
AC9	bats tests/devtools/lint-commit-msg.bats	Passed: wrapper checks exercise capable, absent, old, and unsupported binaries. They verify selected-binary precedence and argument forwarding, with no shell rerun after a Go failure.
AC10	mise run test	Passed on Linux: frozen-shell parity compares status, stdout, stderr, and preview bytes. macOS and Windows await native CI.

mise run lint: passed, including generated-payload and script-hygiene checks.

Risk

Identity or temporary-message regressions could block previews. Revert this change to restore shell dispatch.

Compatibility: none

Related

Closes #801.