CI: re-enable Windows and macOS with per-platform isolation

.github/dependabot.yml

@@ -0,0 +1,15 @@
+version: 2
+updates:
+
+  # Covers actions/* and other tagged refs that appear in workflows here.
+  #
+  # It does NOT maintain the PerlToolsTeam/github_workflows SHA pins in
+  # ci.yml. Dependabot only advances a SHA-pinned ref when the upstream repo
+  # publishes tags (dependabot-core github_actions/update_checker.rb,
+  # latest_commit_sha returns early without a latest_version_tag), and that
+  # repo has none. Those pins must be reviewed by hand -- see
+  # docs/ci-pin-maintenance.md.
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/ci.yml

@@ -8,16 +8,28 @@ on:
   workflow_dispatch:
 
 jobs:
+  # Calls the cpan-test composite action directly rather than the cpan-test.yml
+  # reusable workflow: the latter fixes its own matrix strategy at the default
+  # fail-fast: true, which cancels healthy cells when an unrelated one fails and
+  # makes per-platform results unreadable.
   test:
-    uses: PerlToolsTeam/github_workflows/.github/workflows/cpan-test.yml@main
-    with:
-      os: '["ubuntu-latest"]'
-      perl_version: '["5.24", "5.30", "5.36", "5.40"]'
+    runs-on: ${{ matrix.os }}
+    name: Perl ${{ matrix.perl }} on ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ ubuntu-latest, macos-latest, windows-latest ]
+        perl: [ "5.24", "5.30", "5.36", "5.40" ]
+    steps:
+      - uses: PerlToolsTeam/github_workflows/.github/actions/cpan-test@b4ba4e5553820e802da91d58eba295575945ad95 # main @ 2026-06-23
+        with:
+          perl_version: ${{ matrix.perl }}
+          os: ${{ matrix.os }}
 
   coverage:
-    uses: PerlToolsTeam/github_workflows/.github/workflows/cpan-coverage.yml@main
+    uses: PerlToolsTeam/github_workflows/.github/workflows/cpan-coverage.yml@b4ba4e5553820e802da91d58eba295575945ad95 # main @ 2026-06-23
 
   perlcritic:
-    uses: PerlToolsTeam/github_workflows/.github/workflows/cpan-perlcritic.yml@main
+    uses: PerlToolsTeam/github_workflows/.github/workflows/cpan-perlcritic.yml@b4ba4e5553820e802da91d58eba295575945ad95 # main @ 2026-06-23
     with:
       level: 5

docs/ci-pin-maintenance.md

@@ -0,0 +1,65 @@
+# CI pin maintenance
+
+`.github/workflows/ci.yml` pins every `PerlToolsTeam/github_workflows`
+reference to a commit SHA rather than `@main`.
+
+## Why pinned
+
+Tracking `@main` meant upstream could change this repository's CI with no
+commit here. That is not hypothetical: PDF-Reuse lost Windows CI for six
+months to an upstream regression, and the eventual fix arrived the same way.
+Neither event produced a commit in any of these repositories, and both were
+found only by re-measuring months later.
+
+## Why this needs a human
+
+**Dependabot does not maintain these pins.** It advances a SHA-pinned GitHub
+Actions ref only when the upstream repository publishes tags — see
+`github_actions/lib/dependabot/github_actions/update_checker.rb` in
+dependabot-core, where `latest_commit_sha` returns early unless
+`latest_version_tag` is present. `PerlToolsTeam/github_workflows` has no
+tags, so no update PR is ever opened for these refs.
+
+The `.github/dependabot.yml` in this repo is still useful — it covers tagged
+`actions/*` refs — but it is inert for the pins below.
+
+## What the pin does and does not freeze
+
+Frozen: the `PerlToolsTeam/github_workflows` files themselves (the composite
+action and the reusable workflows).
+
+Not frozen:
+
+- Actions invoked *inside* the pinned upstream files, which use tag refs.
+  In the composite action: `actions/checkout@v5`,
+  `shogo82148/actions-setup-perl@v1`, `ilammy/msvc-dev-cmd@v1`,
+  `actions/upload-artifact@v5`. In the coverage and perlcritic reusable
+  workflows: `actions/checkout@v7`. Tags can move.
+- Container images in the coverage and perlcritic workflows
+  (`davorg/perl-coveralls:latest`, `davorg/perl-perlcritic`), which float.
+
+So the pin is a boundary around one upstream repository, not a full CI lock.
+It removes the failure mode that actually bit us; it does not make CI
+bit-for-bit reproducible.
+
+## How to review the pin
+
+Roughly quarterly, or when CI behaves unexpectedly:
+
+    gh api repos/PerlToolsTeam/github_workflows/commits/main \
+      --jq '"\(.sha)  \(.commit.author.date)  \(.commit.message|split("\n")[0])"'
+
+Compare against the SHA in `ci.yml`. To see what changed since the pin:
+
+    gh api "repos/PerlToolsTeam/github_workflows/commits?sha=main&since=<pin-date>" \
+      --jq '.[] | "\(.commit.author.date)  \(.sha[0:8])  \(.commit.message|split("\n")[0])"'
+
+To advance: update all three refs in `ci.yml` plus the trailing
+`# main @ <date>` comments, push to a branch, and let the PR's own CI run be
+the verification. Do not advance a pin without a green run — the point of the
+pin is that upstream changes arrive as a reviewable event rather than a
+surprise.
+
+Keep the same SHA across all five distributions (PDF-Reuse, PDF-Reuse-Barcode,
+PDF-Reuse-OverlayChart, PDF-Reuse-Tutorial, Business-US-USPS-IMB) so a
+divergence between them is always a signal rather than noise.