diff --git a/build/tasks/verify/verify-workflows.mts b/build/tasks/verify/verify-workflows.mts
new file mode 100644
index 00000000..4e7b69a0
--- /dev/null
+++ b/build/tasks/verify/verify-workflows.mts
@@ -0,0 +1,203 @@
+/**
+ * @file Verify the workflows pin what they run to something immutable.
+ * @author The OpenINF Authors & Friends
+ * @license MIT OR Apache-2.0 OR BlueOak-1.0.0
+ * @module {type ES6Module} build/tasks/verify/verify-workflows
+ *
+ * Two of these files say "Actions are pinned by commit, never by tag" and
+ * nothing has been checking it. A tag is a name its owner can move, so an
+ * action referenced by one is code that can change under a workflow holding a
+ * token -- which for `commit-queue.yml` is a token that can merge.
+ *
+ * Actions are read as text, because the version a commit belongs to lives in
+ * a trailing comment, which parsing throws away, and that comment is both how
+ * a reader knows what is pinned and how renovate knows what to move it to.
+ *
+ * Images are read from parsed YAML, because they are not one shape. A job may
+ * write `container: name`, or `container: {image: name}`, or name several
+ * under `services:` -- and a line-oriented reader that knew only `image:`
+ * would pass the first of those without looking, which is how a check comes
+ * to be worth less than the confidence people place in it.
+ */
+
+import { readFile } from 'node:fs/promises';
+import { glob } from '@openinf/.github/build/utils';
+import { isPair, isScalar, parseDocument, visit } from 'yaml';
+
+/** What a job may say about the containers it runs in, and what it runs. */
+
+/** What a commit looks like, and nothing else does. */
+const COMMIT = /^[0-9a-f]{40}$/;
+
+/**
+ * A digest, which is how an image is named immutably. The name before it may
+ * carry a registry with a port -- `registry.example:5000/team/tool` -- so the
+ * only colon that matters is the one introducing the digest.
+ */
+const DIGEST = /@sha256:[0-9a-f]{64}$/;
+
+/** The trailing comment naming what the pin is, as `# v4.1.2` or `# latest`. */
+const VERSION_COMMENT = /#\s*\S+/;
+
+type Job = {
+  container?: string | { image?: string };
+  services?: Record<string, { image?: string } | undefined>;
+  steps?: { uses?: string }[];
+  uses?: string;
+};
+
+/** One `uses:` value, and where the file says it. */
+type Use = { action: string; line: number; trailing: string };
+
+/**
+ * Collects everything a workflow runs from somebody else's repository, and
+ * where each is written.
+ *
+ * Taken from the parsed document rather than from the lines, because YAML has
+ * more ways to write a key than a reader expects: `- "uses": owner/action@v1`
+ * is the same step as the bare spelling and GitHub runs it just the same,
+ * while a pattern looking for `uses:` walks straight past it.
+ *
+ * The position comes from the document as well. Searching the text for the
+ * value instead would find whichever line mentions it first -- a commented-out
+ * copy above the real one, say -- and read that line's version comment as
+ * though it belonged to the reference below.
+ * @param {string} text The workflow as written.
+ * @returns {Use[]} The action references, with their line and what trails them.
+ */
+function usesIn(text: string) {
+  const found: Use[] = [];
+
+  // The plain-function visitor rather than the keyed one: `{ Pair() {} }` is
+  // the library's own spelling, and the naming rule reads it as a method that
+  // should be camelCase.
+  visit(parseDocument(text), (_, node) => {
+    if (!isPair(node)) return;
+
+    const { key, value } = node as { key: unknown; value: unknown };
+
+    if (
+      !isScalar(key) ||
+      key.value !== 'uses' ||
+      !isScalar(value) ||
+      typeof value.value !== 'string' ||
+      value.range == null
+    ) {
+      return;
+    }
+
+    const start = value.range[0];
+    const valueEnd = value.range[1];
+    const newline = text.indexOf('\n', valueEnd);
+
+    found.push({
+      action: value.value,
+      line: text.slice(0, start).split('\n').length,
+      trailing: text.slice(valueEnd, newline === -1 ? undefined : newline),
+    });
+  });
+
+  return found;
+}
+
+/**
+ * Collects every image a workflow runs, whichever way it names them.
+ * @param {unknown} document The parsed workflow.
+ * @returns {string[]} The image references found in it.
+ */
+function imagesIn(document: unknown) {
+  const jobs = (document as { jobs?: Record<string, Job> } | null)?.jobs ?? {};
+  const images: string[] = [];
+
+  for (const job of Object.values(jobs)) {
+    const container = job?.container;
+
+    if (typeof container === 'string') images.push(container);
+    else if (typeof container?.image === 'string') images.push(container.image);
+
+    for (const service of Object.values(job?.services ?? {})) {
+      if (typeof service?.image === 'string') images.push(service.image);
+    }
+  }
+
+  return images;
+}
+
+// GitHub reads both extensions, so a check that reads one is a check with a
+// way around it.
+const files = await glob([
+  '.github/workflows/*.yml',
+  '.github/workflows/*.yaml',
+]);
+const problems: string[] = [];
+
+// A pattern that matches nothing would otherwise report that everything this
+// project runs is pinned, having read no workflows at all -- the shape of
+// answer a check must never give, and the one `verify.unit` has guarded
+// against from the start.
+if (files.length === 0) {
+  console.error(
+    'No workflows matched `.github/workflows/*.{yml,yaml}`. Nothing was checked, so nothing is known to be pinned.'
+  );
+  process.exit(1);
+}
+
+for (const file of files) {
+  const text = await readFile(file, 'utf8');
+
+  for (const { action, line, trailing } of usesIn(text)) {
+    // A path inside this repository is not a third party and has no commit of
+    // its own to name.
+    if (action.startsWith('./')) continue;
+
+    const where = `${file}:${line}`;
+
+    // `uses: docker://image` runs a container rather than an action, so it is
+    // named the way containers are -- by digest, not by commit. Read as an
+    // action it looks like a pin to `sha256:…`, and the check would refuse a
+    // reference that is already immutable.
+    if (action.startsWith('docker://')) {
+      const image = action.slice('docker://'.length);
+
+      if (!DIGEST.test(image)) {
+        problems.push(
+          `${where}: the container image "${image}" is not pinned to a digest. A tag is a name its owner can repoint at other code.`
+        );
+      }
+
+      continue;
+    }
+
+    const at = action.lastIndexOf('@');
+    const name = at === -1 ? action : action.slice(0, at);
+    const ref = at === -1 ? '' : action.slice(at + 1);
+
+    if (!COMMIT.test(ref)) {
+      problems.push(
+        `${where}: ${name} is pinned to "${ref}", which is a tag or a branch. A tag can be moved by whoever owns it; a commit cannot.`
+      );
+    } else if (!VERSION_COMMENT.test(trailing)) {
+      problems.push(
+        `${where}: ${name} is pinned to a commit with no trailing comment saying which version that is. Nobody can read the pin, and renovate has nothing to move.`
+      );
+    }
+  }
+
+  for (const image of imagesIn(parseDocument(text).toJS())) {
+    if (DIGEST.test(image)) continue;
+
+    problems.push(
+      `${file}: the container image "${image}" is not pinned to a digest. A tag is a name its owner can repoint at other code.`
+    );
+  }
+}
+
+if (problems.length > 0) {
+  console.error('Workflows run code that could change underneath them:\n');
+  for (const problem of problems) console.error(`  ${problem}`);
+  process.exitCode = 1;
+} else {
+  console.log(
+    `Checked ${files.length} workflow${files.length === 1 ? '' : 's'}; everything they run is pinned to a commit or a digest.`
+  );
+}
diff --git a/package-scripts.yml b/package-scripts.yml
index 8e08cb27..fd036d07 100644
--- a/package-scripts.yml
+++ b/package-scripts.yml
@@ -19,6 +19,7 @@ scripts:
     ts: node build/tasks/verify/verify-ts.mts
     unit: node build/tasks/verify/verify-unit.mts
     validForEC: node build/tasks/verify/verify-valid-for-ec.mts
+    workflows: node build/tasks/verify/verify-workflows.mts
     yaml: node build/tasks/verify/verify-yaml.mts
   format:
     all: 'rc=0; for i in build/tasks/format/*.mts; do node "$i" || rc=1; done; exit $rc'
diff --git a/package.json b/package.json
index eb568127..998edf50 100644
--- a/package.json
+++ b/package.json
@@ -77,6 +77,7 @@
     "retext-syntax-mentions": "4.0.0",
     "retext-syntax-urls": "4.0.0",
     "typescript": "7.0.2",
-    "unified": "11.0.5"
+    "unified": "11.0.5",
+    "yaml": "2.9.0"
   }
 }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 51587748..1a49048c 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -158,6 +158,9 @@ importers:
       unified:
         specifier: 11.0.5
         version: 11.0.5
+      yaml:
+        specifier: 2.9.0
+        version: 2.9.0
 
 packages:
 
diff --git a/project-terms.txt b/project-terms.txt
index d7c3d397..0698774e 100644
--- a/project-terms.txt
+++ b/project-terms.txt
@@ -72,6 +72,7 @@ recompiles
 remarkrc
 Renovatebot
 renovaterc
+repoint
 repoints
 retarget
 retargets