Git.commit: CommitOptions.date only sets the author date, not the committer date

[joewalker]

Observed behavior

Git.commit in src/util/git.ts forwards options.date as --date=<iso> to git:

if (date != null) {
  args.push(`--date=${new Date(date).toISOString()}`);
}

Git's --date flag only sets the AUTHOR date. The committer date defaults to "now" unless GIT_COMMITTER_DATE is set. Because the API exposes a single date, callers will reasonably assume it sets the commit's timestamp, but only one of the two timestamps actually changes.

Expected behavior

A single date option should set both author and committer dates so the resulting commit is fully deterministic, or the option should be renamed/split to make the asymmetry explicit.

Minimal reproduction

const date = new Date('1970-01-01T00:00:00Z').getTime();
await git.commit('msg', {
  committer: { name: 'X', email: 'x@y' },
  date,
});
// git log -1 --format='AD=%ai CD=%ci'
// -> AD=1970-01-01 00:00:00 +0000  CD=2026-05-25 19:25:44 +0100

Verified with a standalone Node script that replicates the exact spawn arguments used by Git.commit.

Suggested fix

Set both timestamps via environment variables, which avoids relying on the asymmetric --date flag:

if (date != null) {
  const iso = new Date(date).toISOString();
  env['GIT_AUTHOR_DATE'] = iso;
  env['GIT_COMMITTER_DATE'] = iso;
}

Add a regression test that commits with a date and asserts both %ai and %ci match.