ci: parallelize cached artifact delivery

.gitea/actions/quickstack-oci/action.yml

@@ -5,6 +5,14 @@ inputs:
     description: Path to the repository deployment manifest.
     required: false
     default: .quickstack/deploy.json
+  mode:
+    description: Execute the complete action, one artifact build slot or only the deployment coordinator.
+    required: false
+    default: all
+  artifact-index:
+    description: Zero-based artifact index used when mode is build.
+    required: false
+    default: "0"
 runs:
   using: composite
   steps:
@@ -12,4 +20,6 @@ runs:
       shell: bash
       env:
         QUICKSTACK_DEPLOY_CONFIG: ${{ inputs.config-path }}
+        QUICKSTACK_ACTION_MODE: ${{ inputs.mode }}
+        QUICKSTACK_ARTIFACT_INDEX: ${{ inputs.artifact-index }}
       run: node "$GITHUB_ACTION_PATH/deploy.mjs"

.gitea/actions/quickstack-oci/deploy.mjs

@@ -374,6 +374,32 @@ function validateImagePath(value, name) {
   return image;
 }
 
+function normalizeBuildSecrets(buildSecrets = {}) {
+  if (buildSecrets === null || typeof buildSecrets !== "object" || Array.isArray(buildSecrets)) {
+    throw new Error("buildSecrets must be an object.");
+  }
+  return Object.fromEntries(
+    Object.entries(buildSecrets).map(([id, rawEnvironmentName]) => {
+      if (!/^[A-Za-z0-9_.-]+$/.test(id)) throw new Error(`Invalid BuildKit secret ID ${id}.`);
+      const environmentName = String(rawEnvironmentName);
+      if (!/^[A-Za-z_][A-Za-z0-9_]*$/.test(environmentName)) {
+        throw new Error(`Invalid Actions secret environment name for BuildKit secret ${id}.`);
+      }
+      return [id, environmentName];
+    }),
+  );
+}
+
+export function resolveBuildSecretArguments(buildSecrets = {}, environment = process.env) {
+  return Object.entries(normalizeBuildSecrets(buildSecrets)).flatMap(([id, environmentName]) => {
+    const value = environment[environmentName];
+    if (value === undefined || String(value).length === 0) {
+      throw new Error(`Missing Actions secret ${environmentName} for BuildKit secret ${id}.`);
+    }
+    return ["--secret", `id=${id},env=${environmentName}`];
+  });
+}
+
 export function validateArtifact(artifact) {
   const name = requiredString(artifact.name, "Artifact name");
   const requiredFiles = (artifact.requiredFiles ?? []).map((file) => {
@@ -396,6 +422,7 @@ export function validateArtifact(artifact) {
     dockerfile: safeRelative(artifact.dockerfile ?? "Dockerfile", `Dockerfile for ${name}`),
     context: safeRelative(artifact.context ?? ".", `Build context for ${name}`),
     buildArgs,
+    buildSecrets: normalizeBuildSecrets(artifact.buildSecrets),
     requiredFiles,
   };
 }
@@ -514,6 +541,27 @@ export function resolvePullRequestHeadBranch({ environment = process.env, eventP
   return requiredString(payload?.pull_request?.head?.ref, "Pull request head branch");
 }
 
+export function isSameRepositoryPullRequest({ eventName, environment = process.env, eventPayload } = {}) {
+  if (eventName !== "pull_request") return false;
+
+  let payload = eventPayload;
+  if (payload === undefined) {
+    const eventPath = String(environment.GITHUB_EVENT_PATH || environment.GITEA_EVENT_PATH || "").trim();
+    if (eventPath) {
+      payload = JSON.parse(fs.readFileSync(eventPath, "utf8"));
+    }
+  }
+  const baseRepository = String(
+    environment.GITHUB_REPOSITORY ||
+      environment.GITEA_REPOSITORY ||
+      payload?.repository?.full_name ||
+      payload?.pull_request?.base?.repo?.full_name ||
+      "",
+  ).trim();
+  const headRepository = String(payload?.pull_request?.head?.repo?.full_name || "").trim();
+  return Boolean(baseRepository && headRepository && baseRepository === headRepository);
+}
+
 export function classifyVersion2Execution(pipeline, eventName) {
   if (eventName === "pull_request") {
     return pipeline.strategy === "promote" ? "validate-candidate" : "build-validation";
@@ -521,6 +569,22 @@ export function classifyVersion2Execution(pipeline, eventName) {
   return pipeline.strategy === "candidate" ? "build-deploy" : "promote";
 }
 
+export function resolveActionMode(value = "all") {
+  const mode = String(value || "all").trim().toLowerCase();
+  if (!new Set(["all", "build", "coordinate"]).has(mode)) {
+    throw new Error(`Unsupported QuickStack action mode ${mode}.`);
+  }
+  return mode;
+}
+
+export function resolveArtifactIndex(value = "0") {
+  const index = Number(value);
+  if (!Number.isInteger(index) || index < 0) {
+    throw new Error("QuickStack artifact index must be a non-negative integer.");
+  }
+  return index;
+}
+
 export function validatePromotionPullRequestSource(pipeline, headBranch) {
   const sourceBranch = requiredString(pipeline.source?.branch, "Promotion source branch");
   const actualHeadBranch = requiredString(headBranch, "Pull request head branch");
@@ -543,6 +607,24 @@ function dockerLogin(registry, dockerEnv) {
   );
 }
 
+function ensureBuildxBuilder(dockerEnv) {
+  const builder = "quickstack-registry-cache";
+  const existing = spawnSync(
+    "docker",
+    ["buildx", "inspect", builder],
+    { env: dockerEnv, encoding: "utf8", stdio: "ignore" },
+  );
+  if (existing.status !== 0) {
+    run(
+      "docker",
+      ["buildx", "create", "--name", builder, "--driver", "docker-container"],
+      { env: dockerEnv },
+    );
+  }
+  run("docker", ["buildx", "inspect", "--bootstrap", builder], { env: dockerEnv });
+  return builder;
+}
+
 function exactDigestFromPush(pushOutput, taggedImage) {
   const digest = [...pushOutput.matchAll(/digest:\s*(sha256:[0-9a-f]{64})/g)].at(-1)?.[1];
   if (!digest) throw new Error(`Registry did not return a digest for ${taggedImage}.`);
@@ -555,10 +637,20 @@ function verifyRequiredContainerFiles(taggedImage, requiredFiles, options) {
   }
 }
 
-function buildArtifact({ artifact, registry, sha, workspace, dockerEnv, validationOnly }) {
+function buildArtifact({
+  artifact,
+  registry,
+  sha,
+  workspace,
+  dockerEnv,
+  validationOnly,
+  useRegistryCache = !validationOnly,
+}) {
   const taggedImage = `${registry}/${artifact.image}:sha-${sha}`;
+  const cacheImage = `${registry}/${artifact.image}:buildcache`;
+  const builder = ensureBuildxBuilder(dockerEnv);
   const buildArgs = [
-    "build", "--progress=plain", "--file", artifact.dockerfile,
+    "buildx", "build", "--builder", builder, "--load", "--progress=plain", "--file", artifact.dockerfile,
     "--label", `org.opencontainers.image.source=${process.env.GITHUB_SERVER_URL ?? process.env.GITEA_SERVER_URL}/${process.env.GITHUB_REPOSITORY ?? process.env.GITEA_REPOSITORY}`,
     "--label", `org.opencontainers.image.revision=${sha}`,
     "--tag", taggedImage,
@@ -566,6 +658,18 @@ function buildArtifact({ artifact, registry, sha, workspace, dockerEnv, validati
   for (const [key, value] of Object.entries(artifact.buildArgs)) {
     buildArgs.push("--build-arg", `${key}=${expandTokens(value, { sha })}`);
   }
+  buildArgs.push(...resolveBuildSecretArguments(artifact.buildSecrets, dockerEnv));
+  if (useRegistryCache) {
+    buildArgs.push("--cache-from", `type=registry,ref=${cacheImage}`);
+    if (!validationOnly) {
+      buildArgs.push(
+        "--cache-to", `type=registry,ref=${cacheImage},mode=max,ignore-error=true`,
+      );
+      console.log(`Using read-write max-mode registry build cache ${cacheImage}.`);
+    } else {
+      console.log(`Using read-only registry build cache ${cacheImage}.`);
+    }
+  }
   buildArgs.push(artifact.context);
   console.log(`Building ${artifact.name} from ${artifact.dockerfile} as ${taggedImage}.`);
   run("docker", buildArgs, { cwd: workspace, env: dockerEnv });
@@ -577,46 +681,11 @@ function buildArtifact({ artifact, registry, sha, workspace, dockerEnv, validati
   return { artifact, taggedImage, digest, exactImage: `${registry}/${artifact.image}@${digest}` };
 }
 
-const PROMOTION_PR_CANDIDATE_PULL_ATTEMPTS = 40;
+function pullCandidateArtifact({ artifact, registry, sourceSha, workspace, dockerEnv }) {
-const PROMOTION_PR_CANDIDATE_PULL_RETRY_MS = 10_000;
-
-export async function pullCandidateArtifact({
-  artifact,
-  registry,
-  sourceSha,
-  workspace,
-  dockerEnv,
-  pullAttempts = 1,
-  pullRetryMs = 0,
-  runCommand = run,
-  sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms)),
-}) {
   const taggedImage = `${registry}/${artifact.image}:sha-${sourceSha}`;
-  if (!Number.isInteger(pullAttempts) || pullAttempts < 1) {
+  run("docker", ["pull", taggedImage], { cwd: workspace, env: dockerEnv });
-    throw new Error("Candidate pull attempts must be a positive integer.");
-  }
-  if (!Number.isFinite(pullRetryMs) || pullRetryMs < 0) {
-    throw new Error("Candidate pull retry delay must be a non-negative number.");
-  }
-  for (let attempt = 1; attempt <= pullAttempts; attempt += 1) {
-    try {
-      runCommand("docker", ["pull", taggedImage], { cwd: workspace, env: dockerEnv });
-      break;
-    } catch (error) {
-      if (attempt === pullAttempts) {
-        throw new Error(
-          `Candidate ${taggedImage} did not become available after ${pullAttempts} attempt(s).`,
-          { cause: error },
-        );
-      }
-      console.log(
-        `Candidate ${taggedImage} is not available yet (${attempt}/${pullAttempts}); retrying in ${pullRetryMs}ms.`,
-      );
-      await sleep(pullRetryMs);
-    }
-  }
   verifyRequiredContainerFiles(taggedImage, artifact.requiredFiles, { cwd: workspace, env: dockerEnv });
-  const repoDigests = runCommand(
+  const repoDigests = run(
     "docker",
     ["image", "inspect", "--format", "{{range .RepoDigests}}{{println .}}{{end}}", taggedImage],
     { cwd: workspace, env: dockerEnv, capture: true },
@@ -665,7 +734,24 @@ function promoteArtifactAliases(artifacts, releaseTag, options) {
 }
 
 async function deployApplications({ applications, artifacts, sha, client }) {
-  for (const application of applications) {
+  const pending = new Map(applications.map((application) => [application.name, application]));
+  const completed = new Set();
+
+  while (pending.size > 0) {
+    const wave = applications.filter(
+      (application) =>
+        pending.has(application.name) &&
+        application.dependsOn.every((dependency) => completed.has(dependency)),
+    );
+    if (wave.length === 0) {
+      throw new Error(
+        `Unable to resolve deployment dependencies for: ${[...pending.keys()].join(", ")}`,
+      );
+    }
+
+    console.log(`Deploying application wave: ${wave.map((application) => application.name).join(", ")}.`);
+    await Promise.all(
+      wave.map(async (application) => {
         const artifact = artifacts.get(application.artifact);
         const environment = {
           ...Object.fromEntries(
@@ -688,10 +774,24 @@ async function deployApplications({ applications, artifacts, sha, client }) {
         });
         console.log(`Deployed ${application.name}: ${result.image}`);
         appendSummary(`- ${application.name}: \`${result.image}\` (${result.status})`);
+      }),
+    );
+    for (const application of wave) {
+      pending.delete(application.name);
+      completed.add(application.name);
+    }
   }
 }
 
-async function executeVersion2({ config, pipeline, eventName, sha, workspace }) {
+async function executeVersion2({
+  config,
+  pipeline,
+  eventName,
+  sha,
+  workspace,
+  actionMode = "all",
+  artifactIndex = 0,
+}) {
   const commitMessage = run("git", ["log", "-1", "--pretty=%B"], { cwd: workspace, capture: true });
   const validationOnly = eventName === "pull_request";
   const skipMarker = pipeline.strategy === "promote"
@@ -703,10 +803,68 @@ async function executeVersion2({ config, pipeline, eventName, sha, workspace })
   }
   const registry = requiredString(config.registry ?? "gitea.nuvisphere.de", "OCI registry").replace(/\/$/, "");
   const dockerConfig = fs.mkdtempSync(path.join(os.tmpdir(), "quickstack-docker-"));
-  const dockerEnv = { ...process.env, DOCKER_CONFIG: dockerConfig };
+  const dockerEnv = { ...process.env, DOCKER_CONFIG: dockerConfig, DOCKER_BUILDKIT: "1" };
   const execution = classifyVersion2Execution(pipeline, eventName);
+  const useRegistryCache =
+    execution !== "build-validation" ||
+    isSameRepositoryPullRequest({ eventName, environment: process.env });
   try {
-    if (execution !== "build-validation") dockerLogin(registry, dockerEnv);
+    const needsRegistryLogin =
+      !(actionMode === "coordinate" && execution === "build-validation") &&
+      (execution !== "build-validation" || useRegistryCache);
+    if (needsRegistryLogin) dockerLogin(registry, dockerEnv);
+
+    if (actionMode === "build") {
+      if (execution !== "build-validation" && execution !== "build-deploy") {
+        console.log(`Artifact build slot ${artifactIndex} is not needed for ${execution}.`);
+        return;
+      }
+      const artifact = pipeline.artifacts[artifactIndex];
+      if (!artifact) {
+        console.log(`Artifact build slot ${artifactIndex} is unused for ${pipeline.name ?? pipeline.branch}.`);
+        return;
+      }
+      const built = buildArtifact({
+        artifact,
+        registry,
+        sha,
+        workspace,
+        dockerEnv,
+        validationOnly: execution === "build-validation",
+        useRegistryCache,
+      });
+      appendSummary(
+        execution === "build-validation"
+          ? `Validated OCI artifact \`${artifact.name}\` for \`${pipeline.branch}\`.`
+          : `Built OCI artifact \`${artifact.name}\`: \`${built.exactImage}\`.`,
+      );
+      return;
+    }
+
+    if (actionMode === "coordinate" && execution === "build-validation") {
+      appendSummary(`Validated ${pipeline.artifacts.length} immutable OCI artifact build(s) for \`${pipeline.branch}\`.`);
+      return;
+    }
+
+    if (actionMode === "coordinate" && execution === "build-deploy") {
+      const artifacts = new Map();
+      for (const artifact of pipeline.artifacts) {
+        artifacts.set(artifact.name, pullCandidateArtifact({
+          artifact,
+          registry,
+          sourceSha: sha,
+          workspace,
+          dockerEnv,
+        }));
+      }
+      const client = createQuickStackClient({
+        baseUrl: process.env.QUICKSTACK_BASE_URL,
+        token: process.env.QUICKSTACK_API_TOKEN,
+      });
+      await deployApplications({ applications: pipeline.applications, artifacts, sha, client });
+      return;
+    }
+
     if (execution === "build-validation" || execution === "build-deploy") {
       const artifacts = new Map();
       for (const artifact of pipeline.artifacts) {
@@ -717,6 +875,7 @@ async function executeVersion2({ config, pipeline, eventName, sha, workspace })
           workspace,
           dockerEnv,
           validationOnly: execution === "build-validation",
+          useRegistryCache,
         }));
       }
       if (execution === "build-validation") {
@@ -736,14 +895,12 @@ async function executeVersion2({ config, pipeline, eventName, sha, workspace })
       const release = loadRelease(workspace, pipeline.release);
       const artifacts = new Map();
       for (const artifact of pipeline.artifacts) {
-        artifacts.set(artifact.name, await pullCandidateArtifact({
+        artifacts.set(artifact.name, pullCandidateArtifact({
           artifact,
           registry,
           sourceSha: sha,
           workspace,
           dockerEnv,
-          pullAttempts: PROMOTION_PR_CANDIDATE_PULL_ATTEMPTS,
-          pullRetryMs: PROMOTION_PR_CANDIDATE_PULL_RETRY_MS,
         }));
       }
       console.log(`Validated ${release.tag} against ${artifacts.size} tested candidate artifact(s) from ${sourceBranch} at ${sha}; no rebuild or deployment performed.`);
@@ -755,7 +912,7 @@ async function executeVersion2({ config, pipeline, eventName, sha, workspace })
     const release = loadRelease(workspace, pipeline.release);
     const artifacts = new Map();
     for (const artifact of pipeline.artifacts) {
-      artifacts.set(artifact.name, await pullCandidateArtifact({
+      artifacts.set(artifact.name, pullCandidateArtifact({
         artifact,
         registry,
         sourceSha,
@@ -798,6 +955,8 @@ async function main() {
   const config = JSON.parse(fs.readFileSync(configPath, "utf8"));
   const eventName = process.env.GITHUB_EVENT_NAME ?? process.env.GITEA_EVENT_NAME ?? "";
   const branch = resolveDeploymentBranch({ eventName });
+  const actionMode = resolveActionMode(process.env.QUICKSTACK_ACTION_MODE);
+  const artifactIndex = resolveArtifactIndex(process.env.QUICKSTACK_ARTIFACT_INDEX);
   if (config.version === 2) {
     const pipeline = validateVersion2Pipeline(config, branch);
     if (!pipeline) {
@@ -806,7 +965,19 @@ async function main() {
     }
     const sha = requiredString(process.env.GITHUB_SHA ?? process.env.GITEA_SHA, "Git SHA").toLowerCase();
     if (!/^[0-9a-f]{40,64}$/.test(sha)) throw new Error("Git SHA must be a full hexadecimal commit ID.");
-    await executeVersion2({ config, pipeline, eventName, sha, workspace });
+    await executeVersion2({
+      config,
+      pipeline,
+      eventName,
+      sha,
+      workspace,
+      actionMode,
+      artifactIndex,
+    });
+    return;
+  }
+  if (actionMode === "build") {
+    console.log("Manifest version 1 remains on the coordinator's serial compatibility path.");
     return;
   }
   const deployment = selectDeployment(config, branch);

.gitea/actions/quickstack-oci/deploy.test.mjs

@@ -6,7 +6,9 @@ import {
   deployExactImage,
   expandTokens,
   mergeEnvironment,
-  pullCandidateArtifact,
+  resolveActionMode,
+  resolveArtifactIndex,
+  resolveBuildSecretArguments,
   resolveSecretEnvironment,
   orderApplications,
   resolveDeploymentBranch,
@@ -100,44 +102,14 @@ test("production pull requests validate tested candidates without rebuilding", (
   );
 });
 
-test("production pull requests wait for a concurrently published candidate", async () => {
+test("validates split action modes and artifact build slots", () => {
-  const registry = "gitea.nuvisphere.de";
+  assert.equal(resolveActionMode(undefined), "all");
-  const artifact = {
+  assert.equal(resolveActionMode("BUILD"), "build");
-    name: "webapp",
+  assert.equal(resolveActionMode("coordinate"), "coordinate");
-    image: "innomieter/webapp",
+  assert.throws(() => resolveActionMode("parallel"), /Unsupported QuickStack action mode/);
-    requiredFiles: [],
+  assert.equal(resolveArtifactIndex("2"), 2);
-  };
+  assert.throws(() => resolveArtifactIndex("-1"), /non-negative integer/);
-  const sourceSha = "1234567890abcdef1234567890abcdef12345678";
+  assert.throws(() => resolveArtifactIndex("1.5"), /non-negative integer/);
-  const digest = `sha256:${"a".repeat(64)}`;
-  const sleeps = [];
-  let pullCalls = 0;
-  const runCommand = (_command, args) => {
-    if (args[0] === "pull") {
-      pullCalls += 1;
-      if (pullCalls < 3) throw new Error("manifest unknown");
-      return "";
-    }
-    if (args[0] === "image") {
-      return `${registry}/${artifact.image}@${digest}\n`;
-    }
-    throw new Error(`Unexpected Docker command: ${args.join(" ")}`);
-  };
-
-  const result = await pullCandidateArtifact({
-    artifact,
-    registry,
-    sourceSha,
-    workspace: "/workspace",
-    dockerEnv: {},
-    pullAttempts: 3,
-    pullRetryMs: 25,
-    runCommand,
-    sleep: async (ms) => sleeps.push(ms),
-  });
-
-  assert.equal(pullCalls, 3);
-  assert.deepEqual(sleeps, [25, 25]);
-  assert.equal(result.exactImage, `${registry}/${artifact.image}@${digest}`);
 });
 
 test("validates OCI paths and repository-local build paths", () => {
@@ -192,6 +164,34 @@ test("version 2 validates promotion contracts and token expansion", () => {
   );
 });
 
+test("passes declared Actions secrets to Docker only through BuildKit secret mounts", () => {
+  const secretValue = "must-not-appear-in-docker-arguments";
+  const artifact = validateArtifact({
+    name: "web",
+    image: "owner/web",
+    buildSecrets: {
+      "next-server-actions-encryption-key": "NEXT_SERVER_ACTIONS_ENCRYPTION_KEY",
+    },
+  });
+  const args = resolveBuildSecretArguments(artifact.buildSecrets, {
+    NEXT_SERVER_ACTIONS_ENCRYPTION_KEY: secretValue,
+  });
+
+  assert.deepEqual(args, [
+    "--secret",
+    "id=next-server-actions-encryption-key,env=NEXT_SERVER_ACTIONS_ENCRYPTION_KEY",
+  ]);
+  assert.doesNotMatch(JSON.stringify(args), new RegExp(secretValue));
+  assert.throws(
+    () => resolveBuildSecretArguments(artifact.buildSecrets, {}),
+    /Missing Actions secret NEXT_SERVER_ACTIONS_ENCRYPTION_KEY/,
+  );
+  assert.throws(
+    () => validateArtifact({ name: "web", image: "owner/web", buildSecrets: { "../invalid": "SECRET" } }),
+    /Invalid BuildKit secret ID/,
+  );
+});
+
 test("application dependencies reject missing nodes and cycles", () => {
   assert.throws(
     () => orderApplications([{ name: "web", dependsOn: ["missing"] }]),

.gitea/scoped_workflows/quickstack-oci.yml

@@ -13,7 +13,7 @@ concurrency:
 
 jobs:
   build_and_deploy:
-    name: ${{ gitea.event_name == 'pull_request' && 'Validate existing candidate without deployment' || gitea.event_name == 'push' && 'Build, publish and deploy exact candidate' || 'Validate or redeploy declared pipeline' }}
+    name: Build once and deploy exact digest
     runs-on: ubuntu-latest
     permissions:
       contents: write

README.md

@@ -50,6 +50,9 @@ Use manifest version 2 when one image serves multiple applications or Production
       "image": "example/web",
       "dockerfile": "Dockerfile",
       "buildArgs": { "BUILD_SHA": "$sha12" },
+      "buildSecrets": {
+        "framework-build-key": "FRAMEWORK_BUILD_KEY"
+      },
       "requiredFiles": ["/app/server.js"]
     }
   ],
@@ -87,9 +90,18 @@ Use manifest version 2 when one image serves multiple applications or Production
 }
 ```
 
+`buildSecrets` is optional and maps a BuildKit secret mount ID to the name of
+an Actions secret exposed to the workflow environment. Values are passed to
+`docker build` through `--secret id=...,env=...`; they are never included in
+the command line as build arguments. The Dockerfile consumes them with
+`RUN --mount=type=secret,id=<id>,required=true ...`.
+
 Candidate pipelines build every artifact once, push `sha-<commit>`, resolve the registry digest and deploy applications in dependency order. A pull request into a promotion branch must originate from `source.branch`; it pulls and verifies the already tested `sha-<commit>` candidates without rebuilding or deploying them. Promotion pushes require a merge parent with an identical Git tree, pull the existing candidate, verify required container files, add the SemVer alias, deploy the exact digests, create the immutable tag and publish the canonical Gitea release. Tag creation does not trigger another scoped pipeline because the workflow listens only to branch pushes.
 
-When a promotion pull request and its source-branch push start concurrently, the
+Scoped workflows can distribute version 2 artifact builds across independent
-pull-request check waits for the immutable candidate tag to become available.
+runner jobs by invoking the action with `mode: build` and a zero-based
-This bounded retry applies only to promotion pull requests; an actual promotion
+`artifact-index`. A final job invokes `mode: coordinate` after all build jobs.
-still fails immediately when its tested candidate is missing.
+Candidate tags are the synchronization boundary, so exact digests never depend
+on matrix output merging. Published candidates also maintain a per-image
+`buildcache` tag with inline BuildKit metadata for ephemeral runners. Version 1
+manifests remain on the serial coordinator compatibility path.