ceremony/.github/workflows/labels.yml

name: labels
# Reusable half of the labels automation. Triggers and permissions live in
# the caller; docs/CONSUMERS.md carries the complete caller stub.
#
# The caller uses pull_request_target, not pull_request: every PR in this
# family arrives from a fork, where pull_request runs with a READ-ONLY token
# and cannot label anything. _target is safe in this workflow because no PR
# code is ever checked out or executed — scope reads changed paths and the
# path mapping via the API and checks out only the ceremony implementation.
# Keep it that way.
#
# The reconcile sweep lived here until #209. Riding the PR-triggered run
# meant every displacement in the sweep's shared concurrency queue recorded
# a CANCELLED `reconcile` check on some PR — read as red CI by every human
# and agent, though the surviving sweep does the displaced run's work. Two
# field facts made that untenable (crew#250): a displaced run cannot be
# rerun — `gh run rerun`, `--failed`, and `--job` all refuse — so a victim
# PR has no manual escape hatch; and the displacing burst is deterministic,
# one `review_requested` event per panelist per request, so every review
# round displaces runs and the rate scales with panel size. The
# sweep now lives in labels-sweep.yml behind its own caller, and the
# trigger job below is its wake: it fires on every event this caller
# subscribes — the exact surface that used to run reconcile directly — so
# the wake latency (#137) is unchanged, while a displaced sweep cancels on
# the Actions tab, attached to no PR. PR checks show scope + trigger only.
#
# This cannot loop: the trigger's dispatch and the reconciler's label
# writes both use GITHUB_TOKEN. GitHub does not create workflow runs from
# GITHUB_TOKEN-raised events — workflow_dispatch and repository_dispatch
# are the two documented exemptions, which is exactly why the trigger can
# wake the sweep with no PAT anywhere in the path — and the sweep itself
# dispatches nothing. Agent writes use a PAT and therefore do trigger —
# exactly the asymmetry wanted.
on:
  workflow_call:
    inputs:
      sweep_workflow:
        description: >-
          Filename of the consumer's sweep caller — the workflow that
          calls labels-sweep.yml (docs/CONSUMERS.md carries the stub).
          The trigger job dispatches it by this name. Override it only
          when the caller file is not named labels-sweep.yml (ceremony's
          own dogfood names it self-labels-sweep.yml).          
        type: string
        required: false
        default: labels-sweep.yml

env:
  # A called workflow arrives without its repository. Keep this literal pin
  # aligned with the ceremony release consumed by callers (issue #9 D3).
  CEREMONY_SELF_REF: "0.4.0"

jobs:
  scope:
    # Not on labeled/unlabeled: those events change no paths, so scope has
    # nothing new to derive — and label churn is precisely what they are.
    # review_requested/review_request_removed likewise change no paths — they
    # exist to wake the sweep (#137) — and running labeler on them widens
    # exactly the window #130 documents, where a label written during a
    # scope run is clobbered.
    if: >-
      github.event_name == 'pull_request_target' &&
      github.event.action != 'labeled' &&
      github.event.action != 'unlabeled' &&
      github.event.action != 'review_requested' &&
      github.event.action != 'review_request_removed'      
    runs-on: ubuntu-latest
    concurrency:
      group: labels-scope-${{ github.event.pull_request.number }}
      cancel-in-progress: true
    steps:
      # actions/labeler@v5 held this seat until #130. Even with
      # sync-labels: false it wrote the WHOLE label set — PUT of
      # (labels-fetched-at-job-start ∪ derived) — so a label applied while
      # the job ran was silently removed: ceremony#128 lost its `release`,
      # the merge door's declared-intent read, two seconds after the
      # builder set it. v6/v7 write the same way, so the step was replaced
      # rather than repinned. labels-scope reads the consumer's
      # .github/labeler.yml and the changed paths via the API, and its
      # only write is an additive POST of the derived scopes: a label
      # applied mid-job survives by construction.
      #
      # Still no PR code: both checkouts below fetch the ceremony
      # implementation only. The dogfood checkout rides github.sha — the
      # base-branch commit the workflow file itself came from, so the
      # script and workflow can never skew — and doubles as the #11
      # bootstrap: ceremony's own labels must work before any release tag
      # exists for the pinned checkout to fetch.
      - uses: actions/checkout@v4
        if: github.repository == 'heavy-duty/ceremony'
        with:
          repository: ${{ github.repository }}
          ref: ${{ github.sha }}
      - uses: actions/checkout@v4
        if: github.repository != 'heavy-duty/ceremony'
        with:
          repository: heavy-duty/ceremony
          ref: ${{ env.CEREMONY_SELF_REF }}
      - uses: ./actions/labels-scope
        env:
          GH_TOKEN: ${{ github.token }}
          REPO: ${{ github.repository }}
          PR_NUMBER: ${{ github.event.pull_request.number }}
          # the BASE branch commit — a PR must not label itself by editing
          # the mapping it is judged by
          CONFIG_REF: ${{ github.sha }}

  trigger:
    # The sweep's wake (#209). No `if:`: reconcile carried none, so the
    # trigger keeps the whole event surface the caller subscribes —
    # workflow_dispatch of the labels caller itself included. That cannot
    # double-fire bootstrap: this dispatch always carries bootstrap=no, so
    # a dispatched labels caller yields one plain sweep, and the taxonomy
    # bootstrap fires solely on a manual dispatch of the sweep caller
    # (whose input defaults to "yes"). Excluding workflow_dispatch here
    # would instead make a dispatched labels caller do nothing at all —
    # a silent no-op run is worse than a redundant sweep.
    #
    # LOUD on failure — never `|| true`: a red trigger is the
    # misconfiguration alarm. A consumer that bumps the pin without adding
    # the sweep caller (workflow-not-found), without its declared
    # `bootstrap` input (unexpected input), or without `actions: write`
    # on this caller (permission denied) fails HERE, visibly on the PR,
    # instead of silently never sweeping again.
    runs-on: ubuntu-latest
    steps:
      - name: dispatch the sweep
        env:
          GH_TOKEN: ${{ github.token }}
          SWEEP_WORKFLOW: ${{ inputs.sweep_workflow }}
        run: gh workflow run "$SWEEP_WORKFLOW" -R "$GITHUB_REPOSITORY" -f bootstrap=no