alpha to beta: which path produces 10.0.0-beta.1

The v10 train has shipped 86 alphas. Milestone 164 is empty. Flipping one config key looks like the whole job. It is not.

Try it

Why: the bump reads the type only when there is no label yet

// release-please, versioning-strategies/prerelease.ts, as read 2026-09-06 (paraphrased)
bump(version) {
  if (version.preRelease) {            // "alpha.86" is present
    return bumpPrerelease(version.preRelease)   // alpha.86 -> alpha.87, type ignored
  }
  return withType(prereleaseType, 1)   // only from a bare 10.0.0: -> beta.1
}
// determineReleaseType(): a "Release-As: X" note on any commit since the last tag wins over both.

What this PR does

PieceEffect
prerelease-type: betaNothing for this cut. Keeps the label truthful for beta.2 onward (bumpPrerelease increments the trailing number, whatever the type).
Release-As: 10.0.0-beta.1 footer, one commitForces the next release PR to beta.1. Squash setting is COMMIT_MESSAGES, so the footer reaches main.
Expected release PR titlechore(main): release 10.0.0-beta.1. If it reads alpha.87, the footer was lost; a second one-commit PR carrying only the footer fixes it.
Stable pinUnchanged. bump-stable-pin exits 3 on any prerelease, by design.