diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 64809b2..e876d10 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -662,7 +662,9 @@ jobs:
               '--registry=https://registry.npmjs.org'], { encoding: 'utf8' });
             if (existing.status === 0) {
               const integrity = 'sha512-' + createHash('sha512').update(readFileSync(archive)).digest('base64');
-              assert.equal(JSON.parse(existing.stdout), integrity, `${spec} already exists with different contents`);
+              const published = JSON.parse(existing.stdout);
+              assert.deepEqual(Array.isArray(published) ? published : [published], [integrity],
+                `${spec} already exists with different contents`);
               return true;
             }
             let error;
@@ -682,7 +684,7 @@ jobs:
               try { code = JSON.parse(result.stdout).error?.code; } catch {}
               // A concurrent publish may fail in npm's version check or during the PUT.
               let matched = false;
-              for (const delay of code === 'E409' ? [0, 2000, 4000, 8000, 16000] : [0]) {
+              for (const delay of code === 'E409' ? [0, 2000, 4000, 8000, 16000, 30000, 60000, 60000, 60000, 60000] : [0]) {
                 if (delay) await new Promise(resolve => setTimeout(resolve, delay));
                 if (isPublished(spec, archive)) {
                   matched = true;
diff --git a/package.json b/package.json
index 5cda3c0..801cfb8 100644
--- a/package.json
+++ b/package.json
@@ -42,7 +42,8 @@
     "fmt": "prettier --write \"./**/*.{scss,ts}\" &&  prettier --parser angular --write \"./**/*.html\"",
     "release": "np --no-tests --no-publish",
     "prepublishOnly": "npm run build",
-    "test:esm": "rdlabo-check-esm && node --test scripts/presets.test.mjs",
+    "test:esm": "rdlabo-check-esm && node --test scripts/presets.test.mjs && npm run test:release",
+    "test:release": "node --test scripts/release.test.mjs",
     "test:presets": "npm run build && node --test scripts/presets.test.mjs",
     "test:dynamic-colors": "npm --prefix demo run test:dynamic-colors"
   },
diff --git a/scripts/release.test.mjs b/scripts/release.test.mjs
new file mode 100644
index 0000000..afa672f
--- /dev/null
+++ b/scripts/release.test.mjs
@@ -0,0 +1,138 @@
+import assert from 'node:assert/strict';
+import { createHash } from 'node:crypto';
+import { readFileSync } from 'node:fs';
+import test from 'node:test';
+
+const workflow = readFileSync(new URL('../.github/workflows/release.yml', import.meta.url), 'utf8');
+const match = workflow.match(/const isPublished = \(spec, archive\) => \{([\s\S]*?)\n          \};/);
+assert(match, 'Expected the release workflow to define isPublished');
+const archive = Buffer.from('immutable npm candidate archive');
+const integrity = 'sha512-' + createHash('sha512').update(archive).digest('base64');
+const publishCode = workflow.slice(
+  workflow.indexOf('const isPublished ='),
+  workflow.indexOf('\n          JS', workflow.indexOf('const isPublished =')),
+);
+
+const checkPublished = (published) => {
+  const isPublished = new Function('spawnSync', 'assert', 'createHash', 'readFileSync', `return (spec, archive) => {${match[1]}\n};`)(
+    (command, args) => {
+      assert.equal(command, 'npm');
+      assert.equal(args[0], 'view');
+      return { status: 0, stdout: JSON.stringify(published) };
+    },
+    assert,
+    createHash,
+    () => archive,
+  );
+  return isPublished('@rdlabo/ionic-theme-md3@1.0.0-beta.test', 'candidate.tgz');
+};
+
+test('existing npm versions accept matching scalar and singleton-array integrity responses', () => {
+  assert.equal(checkPublished(integrity), true);
+  assert.equal(checkPublished([integrity]), true);
+});
+
+test('existing npm versions reject mismatched, empty, or ambiguous integrity responses', () => {
+  for (const published of ['sha512-other', ['sha512-other'], [], [integrity, integrity], [integrity, 'sha512-other'], null, {}]) {
+    assert.throws(() => checkPublished(published), { code: 'ERR_ASSERTION' });
+  }
+});
+
+const runWorkflow = (spawnSync, setTimeout) => {
+  const AsyncFunction = Object.getPrototypeOf(async () => {}).constructor;
+  const run = new AsyncFunction(
+    'spawnSync',
+    'assert',
+    'createHash',
+    'readFileSync',
+    'archives',
+    'EXPECTED_VERSION',
+    'DIST_TAG',
+    'console',
+    'process',
+    'setTimeout',
+    publishCode,
+  );
+  return run(
+    spawnSync,
+    assert,
+    createHash,
+    () => archive,
+    new Map([['@rdlabo/ionic-theme-md3', 'candidate.tgz']]),
+    '1.0.0-beta.test',
+    'beta',
+    { log() {} },
+    { stdout: { write() {} }, stderr: { write() {} } },
+    setTimeout,
+  );
+};
+
+test('the workflow skips npm publish for matching scalar and singleton-array responses', async () => {
+  for (const published of [integrity, [integrity]]) {
+    const commands = [];
+    await runWorkflow((command, args) => {
+      commands.push(args[0]);
+      assert.equal(command, 'npm');
+      assert.equal(args[0], 'view', 'A matching published archive must skip npm publish');
+      return { status: 0, stdout: JSON.stringify(published) };
+    });
+    assert.deepEqual(commands, ['view']);
+  }
+});
+
+const notVisible = { status: 1, stdout: JSON.stringify({ error: { code: 'E404' } }), stderr: '' };
+
+const simulateConflict = async (resolveView, code = 'E409') => {
+  let views = 0;
+  let publishes = 0;
+  const delays = [];
+  const result = runWorkflow(
+    (command, args) => {
+      assert.equal(command, 'npm');
+      if (args[0] === 'view') return resolveView(++views);
+      assert.equal(args[0], 'publish');
+      publishes++;
+      return { status: 1, stdout: JSON.stringify({ error: { code } }), stderr: '' };
+    },
+    (resolve, delay) => {
+      delays.push(delay);
+      resolve();
+    },
+  );
+  return { result, delays, views: () => views, publishes: () => publishes };
+};
+
+test('E409 checks beyond the old reflection window and accepts a matching array without republishing', async () => {
+  const run = await simulateConflict((view) => (view <= 7 ? notVisible : { status: 0, stdout: JSON.stringify([integrity]) }));
+  await run.result;
+  assert.equal(run.publishes(), 1);
+  assert.equal(run.views(), 8);
+  assert.deepEqual(run.delays, [2000, 4000, 8000, 16000, 30000, 60000]);
+});
+
+test('E409 stops after a bounded five-minute reflection budget', async () => {
+  const run = await simulateConflict(() => notVisible);
+  await assert.rejects(run.result, /no matching public version became visible/);
+  assert.equal(run.publishes(), 1);
+  assert.equal(run.views(), 11);
+  assert.equal(
+    run.delays.reduce((sum, delay) => sum + delay, 0),
+    300000,
+  );
+});
+
+test('other publish errors receive no extended reflection polling', async () => {
+  const run = await simulateConflict(() => notVisible, 'E403');
+  await assert.rejects(run.result, /no matching public version became visible/);
+  assert.equal(run.publishes(), 1);
+  assert.equal(run.views(), 2);
+  assert.deepEqual(run.delays, []);
+});
+
+test('E409 fails immediately when a reflected version has a different integrity', async () => {
+  const run = await simulateConflict((view) => (view === 1 ? notVisible : { status: 0, stdout: JSON.stringify(['sha512-other']) }));
+  await assert.rejects(run.result, /already exists with different contents/);
+  assert.equal(run.publishes(), 1);
+  assert.equal(run.views(), 2);
+  assert.deepEqual(run.delays, []);
+});