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feat(runners): route on fleet liveness, drop rerun-to-hosted branch #86

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Merged
kyle-sexton merged 2 commits into from
Jul 13, 2026
Merged

feat(runners): route on fleet liveness, drop rerun-to-hosted branch #86

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83f90e1
feat(runners): route on fleet liveness, drop rerun-to-hosted branch
kyle-sexton Jul 13, 2026
d1e14eb
fix(runners): retire attempt-2 rerun contract from selector conformance
kyle-sexton Jul 13, 2026
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57 changes: 21 additions & 36 deletions .github/scripts/select-runner.cjs
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@ function hostedResult(hostedRunner, reason) {
runner: hostedRunner || DEFAULT_HOSTED_RUNNER,
route: "hosted",
reason,
idleRunnerCount: 0,
onlineRunnerCount: 0,
});
}

Expand Down Expand Up @@ -156,8 +156,8 @@ function permitsLocalExecution(input) {

function preflight(input) {
// The fallback is itself an untrusted operational value. Canonicalize it
// before every early return so hosted-only, rerun, and security guards can
// never be redirected to a generic or managed self-hosted label.
// before every early return so hosted-only and security guards can never
// be redirected to a generic or managed self-hosted label.
const hosted = canonicalHostedRunner(input);
const hostedRunner = hosted.runner;

Expand All @@ -167,14 +167,6 @@ function preflight(input) {

const selfHostedOnly = input.policy === "self-hosted-only";

if (
!selfHostedOnly &&
Number.isInteger(input.runAttempt) &&
input.runAttempt > 1
) {
return { result: hostedResult(hostedRunner, "rerun") };
}

// Public repositories do not save billed minutes. Only explicitly reviewed
// caller event classes may route locally, and fork/Dependabot code must never
// receive the observer credential. This guard is duplicated on the token-
Expand All @@ -197,11 +189,7 @@ function preflight(input) {
return { result: hostedResult(hostedRunner, "missing-config") };
}

if (
!exactNonEmptyString(input.hostedRunner) ||
!Number.isInteger(input.runAttempt) ||
input.runAttempt < 1
) {
if (!exactNonEmptyString(input.hostedRunner)) {
if (selfHostedOnly) {
throw new StrictRoutingError("missing-config");
}
Expand All @@ -216,9 +204,6 @@ function preflight(input) {
!exactNonEmptyString(input.owner) ||
(input.scope === "repository" &&
!exactNonEmptyString(input.repository)) ||
// Attempts greater than one returned `rerun` above. Requiring exactly
// one here keeps prefer-self-hosted reruns on the hosted route.
input.runAttempt !== 1 ||
!validTimeout)
) {
return { result: hostedResult(hostedRunner, "missing-config") };
Expand Down Expand Up @@ -254,7 +239,7 @@ function preflight(input) {
runner: candidates.labels[0],
route: "self-hosted",
reason: "self-hosted-only",
idleRunnerCount: 0,
onlineRunnerCount: 0,
}),
};
}
Expand All @@ -279,7 +264,6 @@ function validateRunner(runner) {
typeof runner.name !== "string" ||
!exactNonEmptyString(runner.os) ||
typeof runner.status !== "string" ||
typeof runner.busy !== "boolean" ||
(Object.hasOwn(runner, "ephemeral") &&
typeof runner.ephemeral !== "boolean") ||
!Array.isArray(runner.labels) ||
Expand Down Expand Up @@ -380,7 +364,7 @@ function throwIfAborted(signal) {
}
}

function selectIdleCandidate(runners, labels, managedRunnerPrefix) {
function selectOnlineCandidate(runners, labels, managedRunnerPrefix) {
// `runs-on` contains only the selected label, so GitHub may assign any
// runner carrying it. Treat that case-insensitive label as contaminated
// if even one bearer falls outside the managed namespace, reports itself
Expand Down Expand Up @@ -449,7 +433,10 @@ function selectIdleCandidate(runners, labels, managedRunnerPrefix) {
);
const safeLabelKeys = new Set(safeLabels.map((candidate) => candidate.key));

const idleRunners = inventory.filter(({ runner, routingLabelKeys }) => {
// Liveness, not idleness: a busy online runner is proof the fleet is alive,
// and GitHub natively queues the job until a matching runner frees up. Only
// a fully offline fleet falls back to the hosted route.
const onlineRunners = inventory.filter(({ runner, routingLabelKeys }) => {
// GitHub's 2026-03-10 OpenAPI makes `ephemeral` optional, and live list
// responses can omit it. An explicit false is authoritative exclusion;
// omission relies on the governed assumption that the exact prefix and
Expand All @@ -461,19 +448,18 @@ function selectIdleCandidate(runners, labels, managedRunnerPrefix) {
return (
runner.name.startsWith(managedRunnerPrefix) &&
runner.status === "online" &&
runner.busy === false &&
eligibleEphemeralState &&
[...routingLabelKeys].some((labelKey) => safeLabelKeys.has(labelKey))
);
});

const selectedLabel = safeLabels.find((candidate) =>
idleRunners.some(({ routingLabelKeys }) =>
onlineRunners.some(({ routingLabelKeys }) =>
routingLabelKeys.has(candidate.key),
),
);
return {
idleRunnerCount: idleRunners.length,
onlineRunnerCount: onlineRunners.length,
selectedLabel: selectedLabel?.label,
labelNamespaceInvalid:
contaminatedLabelKeys.size > 0 && safeLabels.length === 0,
Expand Down Expand Up @@ -521,22 +507,22 @@ async function selectRunner(input, dependencies = {}) {
controller.signal,
);
throwIfAborted(controller.signal);
const idle = selectIdleCandidate(
const selection = selectOnlineCandidate(
runners,
prepared.labels,
input.managedRunnerPrefix,
);
if (idle.labelNamespaceInvalid) {
if (selection.labelNamespaceInvalid) {
return hostedResult(prepared.hostedRunner, "invalid-response");
}
if (!idle.selectedLabel) {
return hostedResult(prepared.hostedRunner, "no-idle-runner");
if (!selection.selectedLabel) {
return hostedResult(prepared.hostedRunner, "no-online-runner");
}
return Object.freeze({
runner: idle.selectedLabel,
runner: selection.selectedLabel,
route: "self-hosted",
reason: "idle",
idleRunnerCount: idle.idleRunnerCount,
reason: "online",
onlineRunnerCount: selection.onlineRunnerCount,
});
} catch (error) {
return errorResult(error, controller, prepared.hostedRunner);
Expand All @@ -556,7 +542,6 @@ function inputsFromEnvironment(env) {
observerClientID: env.OBSERVER_CLIENT_ID,
hasObserverSecret: env.HAS_OBSERVER_SECRET === "true",
tokenOutcome: env.TOKEN_OUTCOME,
runAttempt: Number(env.RUN_ATTEMPT),
owner: env.REPOSITORY_OWNER,
repository: env.REPOSITORY_NAME,
apiTimeoutSeconds: Number(env.API_TIMEOUT_SECONDS),
Expand All @@ -574,7 +559,7 @@ async function runGitHubScript({ github, core, env }) {
core.setOutput("runner", result.runner);
core.setOutput("route", result.route);
core.setOutput("reason", result.reason);
core.setOutput("idle-runner-count", String(result.idleRunnerCount));
core.setOutput("online-runner-count", String(result.onlineRunnerCount));
return result;
}

Expand All @@ -586,6 +571,6 @@ module.exports = Object.freeze({
permitsLocalExecution,
preflight,
runGitHubScript,
selectIdleCandidate,
selectOnlineCandidate,
selectRunner,
});
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