[CI] Split the CI control labels into four axes and resolve them live (#40527)

.github/scripts/ci-labels.cjs

@@ -0,0 +1,62 @@
+"use strict";
+
+/**
+ * Labels come from the API, not `context.payload`: a rerun replays the original
+ * event, so the payload carries the label set from when the run was created.
+ */
+
+const BYPASS_FAIL_FAST = "bypass-fail-fast";
+const PARALLEL_STAGES = "parallel-stages";
+const MAX_CONCURRENCY = "max-concurrency";
+const HIGHEST_PRIORITY = "highest-priority";
+
+// Callers gate the whole run on this, so a transient API error must not fail them.
+async function readLabels(github, context) {
+  try {
+    return await fetchLabels(github, context);
+  } catch (e) {
+    console.warn(`Could not read PR labels: ${e.message}`);
+    return [];
+  }
+}
+
+async function fetchLabels(github, context) {
+  const prNumber = context.payload.pull_request?.number;
+  if (prNumber) {
+    const { data: pr } = await github.rest.pulls.get({
+      owner: context.repo.owner,
+      repo: context.repo.repo,
+      pull_number: prNumber,
+    });
+    return pr.labels.map((l) => l.name);
+  }
+  const sha = context.payload.pull_request?.head?.sha || context.sha;
+  const { data: prs } =
+    await github.rest.repos.listPullRequestsAssociatedWithCommit({
+      owner: context.repo.owner,
+      repo: context.repo.repo,
+      commit_sha: sha,
+    });
+  return prs.length > 0 ? prs[0].labels.map((l) => l.name) : [];
+}
+
+async function resolveCiLabels(github, context) {
+  const labels = await readLabels(github, context);
+  const has = (name) => labels.includes(name);
+  const highestPriority = has(HIGHEST_PRIORITY);
+  return {
+    labels,
+    bypassFailFast: highestPriority || has(BYPASS_FAIL_FAST),
+    parallelStages: highestPriority || has(PARALLEL_STAGES),
+    maxConcurrency: highestPriority || has(MAX_CONCURRENCY),
+    highestPriority,
+  };
+}
+
+module.exports = {
+  resolveCiLabels,
+  BYPASS_FAIL_FAST,
+  PARALLEL_STAGES,
+  MAX_CONCURRENCY,
+  HIGHEST_PRIORITY,
+};