chore: bump pnpm/action-setup to v6

[tenphi]

Context

This started as "remove corepack" — but there is no corepack in this repo. No corepack enable, no corepack prepare, nothing in the workflows, docs, or scripts. CI already installs pnpm via pnpm/action-setup and pins it with packageManager: pnpm@11.0.8. Companion to tenphi/tasty#265.

Changes

pnpm/action-setup v4 → v6 in all four call sites (ci.yml, deploy-playground.yml, both jobs of release.yml).

Drop-in despite skipping a major: v4 and v6 declare identical inputs and outputs — the only action.yml deltas are a description wording change and the action's own runtime moving node20 → node24. v6 is also the first version that reads devEngines.packageManager, so adopting that declaration later needs no further CI change.

Why packageManager stays (and devEngines.packageManager does not land here)

The forward-looking devEngines.packageManager declaration isn't viable for this repo yet. Verified locally against pnpm 11.22.0 / pnpm 11.0.8 / npm 10.9.7:

• Both fields can't coexist — pnpm warns on every install: Cannot use both "packageManager" and "devEngines.packageManager" in package.json. "packageManager" will be ignored.
• packageManager is consumed here — by pnpm's own version management and by pnpm/action-setup when version is omitted. v4 does not read devEngines at all, so dropping the field before this bump would have broken CI.
• devEngines breaks npm-based publishing. release.yml runs npm pkg set version and npm publish. With devEngines.packageManager: {name: pnpm, …} and onFail: "download" (or "error"), every npm command exits non-zero:

  npm error code EBADDEVENGINES
  npm error EBADDEVENGINES Invalid name "pnpm" does not match "npm" for "packageManager"
  

  Only onFail: "warn"/"ignore" lets npm proceed, and warn prints that block on each npm invocation.
• pnpm 10 ignores it silently. devEngines.packageManager landed in pnpm 11.0, so a contributor on pnpm 10 would get no pin and no error — today packageManager auto-switches them.
• It pulls the pnpm binary into the lockfile. With onFail: "download", pnpm writes packageManagerDependencies plus @pnpm/exe / pnpm / @reflink entries — ~199 extra lines of lockfile.

Verification

Workflow-only change — no manifest or lockfile edits. All three workflow files parse as YAML, and the v4↔v6 input/output comparison above was made against the actions' own action.yml.

Follow-up worth considering (not in this PR)

pnpm/action-setup's README now names a successor: pnpm/setup@v1, recommended for pnpm 11+. It installs pnpm as a standalone native binary and can provision the runtime, replacing actions/setup-node. Bigger change, own PR — and it needs care around release.yml's registry-url setup for publishing.

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Generated by Claude Code

[github-actions]

📦 Snapshot release

Published 0.0.0-snapshot.4b10206.

pnpm add @tenphi/glaze@0.0.0-snapshot.4b10206