diff --git a/.github/workflows/squad-ci.yml b/.github/workflows/squad-ci.yml
index d97a6de86..73ea55d90 100644
--- a/.github/workflows/squad-ci.yml
+++ b/.github/workflows/squad-ci.yml
@@ -174,6 +174,25 @@ jobs:
   # Skip labels: skip-changelog, skip-exports-check, skip-samples-ci,
   # skip-workspace-check, skip-version-check, skip-export-smoke, large-deletion-approved
 
+  # ── Changeset drift gate (#1273) ─────────────────────────────────────────
+  # Alarms when unreleased changeset fragments accumulate (count or age),
+  # i.e. the release flow stopped consuming them. Warn-only on PRs (the PR
+  # author isn't the one who can fix release cadence), hard fail on dev pushes.
+  changeset-drift:
+    name: Changeset Drift
+    if: vars.SQUAD_CHANGESET_DRIFT_CHECK != 'false'
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 #v7
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e #v6
+        with:
+          node-version: 22
+      - name: Check changeset drift
+        run: node scripts/check-changeset-drift.mjs --mode=${{ github.event_name == 'push' && 'fail' || 'warn' }}
+
   # ── Consolidated policy gates ───────────────────────────────────────────
   # Runs changelog, changelog-protection, workspace-integrity,
   # prerelease-version-guard, publish-policy, and scope-check on one runner.
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 8c0eae1c2..ffdac417f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -343,6 +343,8 @@ This:
 
 You don't need to manually version — changesets handle it.
 
+CI watches for drift: `scripts/check-changeset-drift.mjs` warns on PRs and fails on `dev` pushes when more than 25 fragments are pending or the oldest is over 30 days old — a signal that `changeset version` needs to run.
+
 ## Branch Strategy
 
 - **main** — Stable, published releases. All merges include changesets.
diff --git a/scripts/check-changeset-drift.mjs b/scripts/check-changeset-drift.mjs
new file mode 100644
index 000000000..33a4d92fe
--- /dev/null
+++ b/scripts/check-changeset-drift.mjs
@@ -0,0 +1,113 @@
+#!/usr/bin/env node
+
+/**
+ * Changeset Drift Check — fails CI when unreleased changesets accumulate.
+ *
+ * The .changeset/ workflow only works if fragments are consumed by a release
+ * (`changeset version`) at a reasonable cadence. Issue #1273 documented the
+ * failure mode: 104 fragments piled up while the root CHANGELOG sat a full
+ * minor version behind, and nothing in CI noticed.
+ *
+ * Thresholds are deliberately loose — this is a smoke alarm for "the release
+ * flow stopped consuming fragments", not a nag on active development.
+ *
+ * Modes:
+ *   --mode=warn  (default) emit a workflow warning, exit 0
+ *   --mode=fail  emit an error annotation, exit 1
+ *
+ * Issue: bradygaster/squad#1273
+ */
+
+import { readdirSync, existsSync } from 'node:fs';
+import { execFileSync } from 'node:child_process';
+import { join } from 'node:path';
+import { pathToFileURL } from 'node:url';
+
+export const MAX_FRAGMENTS = 25;
+export const MAX_AGE_DAYS = 30;
+
+/**
+ * List pending changeset fragments (markdown files that `changeset version`
+ * would consume). README.md and non-.md files (config.json) are not fragments.
+ */
+export function listFragments(changesetDir) {
+  if (!existsSync(changesetDir)) return [];
+  return readdirSync(changesetDir)
+    .filter((f) => f.endsWith('.md') && f !== 'README.md')
+    .sort();
+}
+
+/**
+ * Age in days of a fragment, measured from the commit that added it.
+ * Untracked or unresolvable files count as age 0 (they can't be stale).
+ */
+export function fragmentAgeDays(repoRoot, fragment, nowMs = Date.now()) {
+  try {
+    const out = execFileSync(
+      'git',
+      ['log', '--diff-filter=A', '--format=%ct', '-1', '--', join('.changeset', fragment)],
+      { cwd: repoRoot, encoding: 'utf8' },
+    ).trim();
+    if (!out) return 0;
+    const addedMs = Number(out) * 1000;
+    if (!Number.isFinite(addedMs) || addedMs <= 0) return 0;
+    return Math.max(0, (nowMs - addedMs) / 86_400_000);
+  } catch {
+    return 0;
+  }
+}
+
+/**
+ * Pure threshold logic — drifted when the pending count exceeds maxFragments
+ * OR the oldest pending fragment exceeds maxAgeDays.
+ */
+export function evaluateDrift({ count, oldestAgeDays, maxFragments = MAX_FRAGMENTS, maxAgeDays = MAX_AGE_DAYS }) {
+  const reasons = [];
+  if (count > maxFragments) {
+    reasons.push(`${count} unreleased changeset fragments (threshold: ${maxFragments})`);
+  }
+  if (oldestAgeDays > maxAgeDays) {
+    reasons.push(`oldest fragment is ${Math.floor(oldestAgeDays)} days old (threshold: ${maxAgeDays})`);
+  }
+  return { drifted: reasons.length > 0, reasons };
+}
+
+function main() {
+  const mode = process.argv.includes('--mode=fail') ? 'fail' : 'warn';
+  const repoRoot = process.cwd();
+  const fragments = listFragments(join(repoRoot, '.changeset'));
+
+  let oldestAgeDays = 0;
+  let oldestName = '';
+  for (const fragment of fragments) {
+    const age = fragmentAgeDays(repoRoot, fragment);
+    if (age > oldestAgeDays) {
+      oldestAgeDays = age;
+      oldestName = fragment;
+    }
+  }
+
+  const { drifted, reasons } = evaluateDrift({ count: fragments.length, oldestAgeDays });
+
+  console.log(`Pending changeset fragments: ${fragments.length} (thresholds: >${MAX_FRAGMENTS} count, >${MAX_AGE_DAYS} days age)`);
+  if (oldestName) {
+    console.log(`Oldest: ${oldestName} (${Math.floor(oldestAgeDays)} days)`);
+  }
+
+  if (!drifted) {
+    console.log('✅ No changeset drift');
+    return;
+  }
+
+  const detail = `${reasons.join('; ')}. Run the release flow (changeset version) or consolidate — see #1273.`;
+  if (mode === 'fail') {
+    console.log(`::error::Changeset drift: ${detail}`);
+    process.exitCode = 1;
+  } else {
+    console.log(`::warning::Changeset drift: ${detail}`);
+  }
+}
+
+if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href) {
+  main();
+}
diff --git a/test/scripts/check-changeset-drift.test.ts b/test/scripts/check-changeset-drift.test.ts
new file mode 100644
index 000000000..96d87e5bd
--- /dev/null
+++ b/test/scripts/check-changeset-drift.test.ts
@@ -0,0 +1,80 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { mkdirSync, rmSync, writeFileSync, existsSync } from 'node:fs';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+import { randomBytes } from 'node:crypto';
+import {
+  listFragments,
+  evaluateDrift,
+  MAX_FRAGMENTS,
+  MAX_AGE_DAYS,
+} from '../../scripts/check-changeset-drift.mjs';
+
+// ── evaluateDrift ───────────────────────────────────────────────────────
+
+describe('evaluateDrift', () => {
+  it('passes when both count and age are under the thresholds', () => {
+    const result = evaluateDrift({ count: MAX_FRAGMENTS, oldestAgeDays: MAX_AGE_DAYS });
+    expect(result.drifted).toBe(false);
+    expect(result.reasons).toEqual([]);
+  });
+
+  it('drifts when the fragment count exceeds the threshold', () => {
+    const result = evaluateDrift({ count: MAX_FRAGMENTS + 1, oldestAgeDays: 0 });
+    expect(result.drifted).toBe(true);
+    expect(result.reasons).toHaveLength(1);
+    expect(result.reasons[0]).toContain(`${MAX_FRAGMENTS + 1} unreleased`);
+  });
+
+  it('drifts when the oldest fragment exceeds the age threshold', () => {
+    const result = evaluateDrift({ count: 1, oldestAgeDays: MAX_AGE_DAYS + 0.5 });
+    expect(result.drifted).toBe(true);
+    expect(result.reasons).toHaveLength(1);
+    expect(result.reasons[0]).toContain('days old');
+  });
+
+  it('reports both reasons when both thresholds are exceeded', () => {
+    const result = evaluateDrift({ count: 104, oldestAgeDays: 90 });
+    expect(result.drifted).toBe(true);
+    expect(result.reasons).toHaveLength(2);
+  });
+
+  it('respects custom thresholds', () => {
+    const result = evaluateDrift({ count: 3, oldestAgeDays: 2, maxFragments: 2, maxAgeDays: 1 });
+    expect(result.drifted).toBe(true);
+    expect(result.reasons).toHaveLength(2);
+  });
+
+  it('passes with zero fragments', () => {
+    const result = evaluateDrift({ count: 0, oldestAgeDays: 0 });
+    expect(result.drifted).toBe(false);
+  });
+});
+
+// ── listFragments ───────────────────────────────────────────────────────
+
+describe('listFragments', () => {
+  const TEST_DIR = join(tmpdir(), `.test-changeset-drift-${randomBytes(4).toString('hex')}`);
+
+  beforeEach(() => {
+    if (existsSync(TEST_DIR)) rmSync(TEST_DIR, { recursive: true, force: true });
+    mkdirSync(TEST_DIR, { recursive: true });
+  });
+
+  afterEach(() => {
+    rmSync(TEST_DIR, { recursive: true, force: true });
+  });
+
+  it('lists .md fragments, excluding README.md and non-markdown files', () => {
+    writeFileSync(join(TEST_DIR, 'brave-lions-jump.md'), '---\n---\n');
+    writeFileSync(join(TEST_DIR, 'happy-owls-sing.md'), '---\n---\n');
+    writeFileSync(join(TEST_DIR, 'README.md'), '# changesets\n');
+    writeFileSync(join(TEST_DIR, 'config.json'), '{}\n');
+
+    expect(listFragments(TEST_DIR)).toEqual(['brave-lions-jump.md', 'happy-owls-sing.md']);
+  });
+
+  it('returns empty for a missing directory', () => {
+    expect(listFragments(join(TEST_DIR, 'does-not-exist'))).toEqual([]);
+  });
+});