feat(runs-on-selector): add runs-on selector action

[yordis]

• Moving one pull request onto other hardware meant editing runs-on in that pull request, so the choice arrived as a change to the workflow rather than as a decision about where to run it.
• Every repository that tried this wrote its own copy of the label parsing, and the copies stopped agreeing on the label vocabulary, which is the drift this repository exists to remove.
• The pool map belongs to the consumer rather than here, so it is an input: no token, no API call, and no permissions.
• An unknown pool name fails the run rather than falling back, because the wrong runner is a green run on hardware nobody chose, and that is expensive to notice.
• The repository resolves its own runner with the action it ships, so a change to the action is exercised by the pull request that makes the change.

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• .github/workflows/ci.yml

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Reviewing files that changed from the base of the PR and between 993cb1e and 6752709.

📒 Files selected for processing (12)

• .config/mise/tasks/github/actions/tests/node
• .github/release-please-config.json
• .github/release-please-manifest.json
• .github/workflows/ci.yml
• actions/runs-on-selector/README.md
• actions/runs-on-selector/action.yml
• actions/runs-on-selector/lib/core.mjs
• actions/runs-on-selector/lib/index.mjs
• actions/runs-on-selector/lib/main.mjs
• mise.toml
• tests/node/runs-on-selector/core.test.mjs
• tests/node/runs-on-selector/index.test.mjs

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Walkthrough

Adds a Node 24 GitHub Action that selects a runner from pull-request labels and a caller-provided pool map. CI resolves the runner before dependent jobs. Tests, documentation, Node tooling, and release metadata are included.

Changes

Runner selection

Layer / File(s)	Summary
Selector action and resolution actions/runs-on-selector/action.yml, actions/runs-on-selector/lib/*	Defines action inputs and outputs. Validates pools and labels, reads pull-request labels, and writes the selected runner and pool.
Runtime helpers actions/runs-on-selector/lib/core.mjs	Adds input, logging, failure, annotation, and workflow-output helpers.
CI runner integration .github/workflows/ci.yml	Adds a resolver job. The check and test jobs use its runs-on output.
Validation and test execution mise.toml, .config/mise/tasks/github/actions/tests/node, tests/node/runs-on-selector/*	Adds Node 24 tooling, a Node test task, and coverage for selection, validation, event parsing, and runtime helpers.
Usage and release registration actions/runs-on-selector/README.md, .github/release-please-config.json, .github/release-please-manifest.json	Documents configuration and selection behavior. Registers the action for release management.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant CI
  participant RunnerSelector
  participant GitHubEvent
  participant DependentJobs
  CI->>RunnerSelector: Provide pool map and default pool
  RunnerSelector->>GitHubEvent: Read pull-request labels
  GitHubEvent-->>RunnerSelector: Return event labels
  RunnerSelector-->>CI: Write runs-on output
  CI->>DependentJobs: Schedule check and test jobs on selected runner

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Merge Risk: ⚪ Minimal · up to 67527

The action selects runners from pull-request labels, validates configuration, and fails safely on invalid selections. No merge-blocking production risk remains evident.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 22.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 18 functions across 5 files. (7 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description directly explains the runs-on selector action, its label-based runner selection, consumer-provided pool map, failure behavior, permissions, and self-testing workflow.
Title check	✅ Passed	The title clearly and concisely identifies the main change: adding the runs-on selector action.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 22.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 18 functions across 5 files. (7 skipped: 7 unsupported.)

✨ Finishing Touches 💡 1

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_{A rabbit maps the pools with care
Labels guide the runner there
Tests hop neatly through the gate
CI selects before they wait
New outputs bloom in lines of light}

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