Adopt scientist-labs/rust-gem-release@v0 for releases

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What

Migrates parsekit's release pipeline to the shared reusable workflow scientist-labs/rust-gem-release, pinned @v0 (the moving-major alias, currently resolving to 0.2.0). This is the same template proven by red-candle 1.8.0, which shipped all four platforms to rubygems.org green on 2026-06-18.

The old .github/workflows/release.yml was a hand-rolled workflow_dispatch-only job that bumped the version, committed + tagged, built a single source gem, and pushed to RubyGems inline. It is replaced by a thin caller that, on a pushed version tag, builds:

• the source gem (universal fallthrough; compiles the native stack on install)
• arm64-darwin precompiled fat gem (native build on Apple Silicon)
• x86_64-linux precompiled fat gem (cross-gem)

Each fat gem carries one compiled extension per Ruby ABI, so consumers install with no Rust toolchain.

Files changed

• .github/workflows/release.yml (modify) — replaced the inline 61-line manual release with the canonical caller uses: scientist-labs/rust-gem-release/.github/workflows/release.yml@v0. Triggers on version tags + workflow_dispatch (publish default false). Inputs: gem-name: parsekit, version-command: ruby -r./lib/parsekit/version -e 'print ParseKit::VERSION', build-aarch64-linux: false, publish: ${{ github.event_name == 'push' || inputs.publish }}; secret rubygems-api-key: ${{ secrets.RUBYGEMS_API_KEY }}; permissions: contents: write.
• lib/parsekit.rb (modify) — PREREQ Bump codecov/codecov-action from 4 to 5 #1: ABI require-shim. Probes parsekit/<major.minor>/parsekit first via $LOAD_PATH require, falling back to flat parsekit/parsekit. The old require_relative "parsekit/parsekit" could never find the extension that a precompiled fat gem installs outside lib/.
• parsekit.gemspec (modify) — PREREQ Bump actions/download-artifact from 4 to 5 #2: env-gated platform branch on RUST_GEM_PLATFORM. When set: spec.platform = it, spec.extensions = [], and the per-ABI .bundle/.so are packed; else declare the ext/parsekit/extconf.rb extension (normal source gem).

ci.yml is kept as the PR-CI path (it curls eng.traineddata and exports TESSDATA_PREFIX, which the shared build.yml has no hook to do); no build.yml caller was added.

Prereqs added

• ABI require-shim in lib/parsekit.rb
• env-gated platform branch (RUST_GEM_PLATFORM) in parsekit.gemspec

Both were absent before this PR — without them the precompiled gems would publish but never load (only the source gem would be usable).

Why aarch64-linux is off

parsekit's native extension statically builds MuPDF and Tesseract + Leptonica from C/C++ source (bundled-tesseract downloads source at build time). The shared workflow's aarch64 leg cross-compiles that bundled-C++ stack on an x86_64 host inside cross-gem's fixed image, which is fragile and may lack network for the source download. build-aarch64-linux: false keeps a tag reliably yielding source + arm64-darwin + x86_64-linux; aarch64 users fall through to the source gem (which compiles on install). Flip it back on once the shared workflow grows a native-arm / prebuilt-sysroot path for C-heavy gems.

Follow-up (not in this PR, non-blocking for the release pipeline): the precompiled gems do not package eng.traineddata, so OCR raises an InitError post-install unless system tessdata exists. Fix consumer-side by packaging or fetching tessdata.

Safety

• publish defaults to a DRY-RUN. On manual workflow_dispatch, publish is false unless explicitly toggled on. Only a real version-tag push sets publish true.
• A tag push is token-gated: if RUBYGEMS_API_KEY is empty the push step is a clean no-op.
• The tag must equal the version-command output (0.1.3); note the constant is ParseKit (capital K).

Template reference: red-candle 1.8.0.

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DRAFT — do not merge until a publish=false dry-run is green; trigger with: gh workflow run release.yml -f publish=false --ref migrate-to-rust-gem-release

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