diff --git a/.changeset/add-storyboard-response-schema-lint.md b/.changeset/add-storyboard-response-schema-lint.md
new file mode 100644
index 0000000000..e6802bcfb6
--- /dev/null
+++ b/.changeset/add-storyboard-response-schema-lint.md
@@ -0,0 +1,4 @@
+---
+---
+
+Add response-side storyboard schema lint (`scripts/lint-storyboard-response-schema.cjs`) that validates `sample_response` fixtures against `response_schema_ref` using AJV, mirroring the existing request-side lint. Includes shrink-only ratchet allowlist, Node test wrapper, and CI wiring. Implements #2823.
diff --git a/package.json b/package.json
index fcb8ea8152..c4eb9696ff 100644
--- a/package.json
+++ b/package.json
@@ -40,6 +40,7 @@
     "test:storyboard-auth-shape": "node --test tests/lint-storyboard-auth-shape.test.cjs",
     "test:storyboard-test-kits": "node --test tests/lint-storyboard-test-kits.test.cjs",
     "test:storyboard-sample-request-schema": "node --test tests/lint-storyboard-sample-request-schema.test.cjs",
+    "test:storyboard-response-schema": "node --test tests/lint-storyboard-response-schema.test.cjs",
     "test:storyboard-doc-parity": "node --test tests/lint-universal-storyboard-doc-parity.test.cjs",
     "test:pagination-invariant": "node --test tests/lint-pagination-invariant.test.cjs",
     "test:test-dynamic-imports": "node --test tests/lint-test-dynamic-imports.test.cjs",
@@ -56,7 +57,7 @@
     "test:docker": "docker compose -f docker-compose.test.yml up --build --abort-on-container-exit",
     "test:docs-nav": "node tests/docs-nav-validation.test.cjs",
     "test:platform-agnostic": "node tests/check-platform-agnostic.cjs",
-    "test": "npm run test:docs-nav && npm run test:schemas && npm run test:examples && npm run test:extensions && npm run test:extension-schemas && npm run test:error-handling && npm run test:json-schema && npm run test:composed && npm run test:migrations && npm run test:hmac-vectors && npm run test:hmac-signer-conformance && npm run test:transport-errors && npm run test:targeting-overlay-vectors && npm run test:storyboard-scoping && npm run test:storyboard-branch-sets && npm run test:storyboard-contradictions && npm run test:storyboard-context-entity && npm run test:storyboard-auth-shape && npm run test:storyboard-test-kits && npm run test:storyboard-sample-request-schema && npm run test:storyboard-doc-parity && npm run test:pagination-invariant && npm run test:test-dynamic-imports && npm run test:build-schemas-hoist-enums && npm run test:error-codes && npm run test:substitution-vector-names && npm run test:platform-agnostic && npm run test:unit && npm run test:server-unit && npm run test:openapi && npm run typecheck",
+    "test": "npm run test:docs-nav && npm run test:schemas && npm run test:examples && npm run test:extensions && npm run test:extension-schemas && npm run test:error-handling && npm run test:json-schema && npm run test:composed && npm run test:migrations && npm run test:hmac-vectors && npm run test:hmac-signer-conformance && npm run test:transport-errors && npm run test:targeting-overlay-vectors && npm run test:storyboard-scoping && npm run test:storyboard-branch-sets && npm run test:storyboard-contradictions && npm run test:storyboard-context-entity && npm run test:storyboard-auth-shape && npm run test:storyboard-test-kits && npm run test:storyboard-sample-request-schema && npm run test:storyboard-response-schema && npm run test:storyboard-doc-parity && npm run test:pagination-invariant && npm run test:test-dynamic-imports && npm run test:build-schemas-hoist-enums && npm run test:error-codes && npm run test:substitution-vector-names && npm run test:platform-agnostic && npm run test:unit && npm run test:server-unit && npm run test:openapi && npm run typecheck",
     "test:all": "npm run test:schemas && npm run test:examples && npm run test:extensions && npm run test:error-handling && npm run test:snippets && npm run typecheck",
     "precommit": "bash scripts/with-timeout.sh 60 npm run test:unit && npm run test:test-dynamic-imports && npm run typecheck",
     "prepare": "husky",
diff --git a/scripts/lint-storyboard-response-schema.cjs b/scripts/lint-storyboard-response-schema.cjs
new file mode 100644
index 0000000000..784dc4d975
--- /dev/null
+++ b/scripts/lint-storyboard-response-schema.cjs
@@ -0,0 +1,372 @@
+#!/usr/bin/env node
+/**
+ * Storyboard sample_response schema conformance lint (issue #2823).
+ *
+ * For every storyboard step that declares both `response_schema_ref` AND
+ * `sample_response`, validate the sample_response against the referenced JSON
+ * schema. This is the response-side twin of lint-storyboard-sample-request-schema.cjs
+ * (see the "future work" note at line 17 of that script).
+ *
+ * Coverage today: inline `sample_response` on the step only. The
+ * comply_scenario-to-fixture mapping (specialism scenarios/*.yaml) is a
+ * runtime runner hint, not a static fixture file — response fixtures from
+ * that path are deferred. The corpus currently has sparse sample_response
+ * coverage; the lint passes vacuously on day 1 and gains CI value as
+ * storyboard authors add sample_response fixtures.
+ *
+ * What it catches (once coverage exists):
+ *   - Response shape drift: fields added/removed between schema and fixture
+ *   - Wrong types, enum violations, required field omissions
+ *   - Stale fixtures that diverge after a schema change
+ *
+ * What it does not catch:
+ *   - Dynamic agent responses (runtime concern, not static lint)
+ *   - Semantic correctness of field values
+ *   - Steps without sample_response (intentionally skipped)
+ */
+
+'use strict';
+
+const fs = require('node:fs');
+const path = require('node:path');
+const yaml = require('js-yaml');
+const Ajv = require('ajv');
+const addFormats = require('ajv-formats');
+
+const STORYBOARD_DIR = path.resolve(__dirname, '..', 'static', 'compliance', 'source');
+const SCHEMA_DIR = path.resolve(__dirname, '..', 'static', 'schemas', 'source');
+const ALLOWLIST_PATH = path.resolve(__dirname, '..', 'tests', 'storyboard-response-schema-allowlist.json');
+
+const schemaCache = new Map();
+
+function schemaRefToPath(ref) {
+  if (!ref) return null;
+  const trimmed = ref.startsWith('/schemas/') ? ref.slice('/schemas/'.length) : ref;
+  return path.join(SCHEMA_DIR, trimmed);
+}
+
+function loadSchema(ref) {
+  const full = schemaRefToPath(ref);
+  if (!full) return null;
+  if (schemaCache.has(full)) return schemaCache.get(full);
+  let doc = null;
+  try {
+    doc = JSON.parse(fs.readFileSync(full, 'utf8'));
+  } catch {
+    doc = null;
+  }
+  schemaCache.set(full, doc);
+  return doc;
+}
+
+function walkYaml(dir) {
+  const out = [];
+  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+    const full = path.join(dir, entry.name);
+    if (entry.isDirectory()) out.push(...walkYaml(full));
+    else if (entry.isFile() && (entry.name.endsWith('.yaml') || entry.name.endsWith('.yml'))) {
+      out.push(full);
+    }
+  }
+  return out;
+}
+
+let sharedAjv = null;
+const validatorCache = new Map();
+
+function getAjv() {
+  if (sharedAjv) return sharedAjv;
+  sharedAjv = new Ajv({
+    allErrors: true,
+    strict: false,
+    discriminator: true,
+    loadSchema: (uri) => {
+      const resolved = loadSchema(uri);
+      if (!resolved) throw new Error(`Cannot resolve $ref: ${uri}`);
+      return Promise.resolve(resolved);
+    },
+  });
+  addFormats(sharedAjv);
+  return sharedAjv;
+}
+
+async function getValidator(schemaRef) {
+  if (validatorCache.has(schemaRef)) return validatorCache.get(schemaRef);
+  const schema = loadSchema(schemaRef);
+  if (!schema) {
+    validatorCache.set(schemaRef, null);
+    return null;
+  }
+  try {
+    const validate = await getAjv().compileAsync(schema);
+    validatorCache.set(schemaRef, validate);
+    return validate;
+  } catch (err) {
+    validatorCache.set(schemaRef, { compileError: err.message });
+    return { compileError: err.message };
+  }
+}
+
+async function validateStep({ schemaRef, payload }) {
+  const schema = loadSchema(schemaRef);
+  if (!schema) {
+    return { ok: false, errors: [{ path: '/', message: `schema not found: ${schemaRef}`, keyword: 'schema_not_found', params: {} }] };
+  }
+  const validate = await getValidator(schemaRef);
+  if (!validate) {
+    return { ok: false, errors: [{ path: '/', message: `schema not found: ${schemaRef}`, keyword: 'schema_not_found', params: {} }] };
+  }
+  if (validate.compileError) {
+    return { ok: false, errors: [{ path: '/', message: `compile error: ${validate.compileError}`, keyword: 'compile_error', params: {} }] };
+  }
+  const valid = validate(payload);
+  if (valid) return { ok: true };
+  return {
+    ok: false,
+    errors: validate.errors.map((e) => ({
+      path: e.instancePath || '/',
+      message: e.message,
+      keyword: e.keyword,
+      params: e.params,
+    })),
+  };
+}
+
+async function lintFile(file) {
+  const violations = [];
+  let skips = 0;
+  let doc;
+  try {
+    doc = yaml.load(fs.readFileSync(file, 'utf8'));
+  } catch (err) {
+    return { violations, skips, parseError: `yaml_parse: ${err.message}` };
+  }
+  const phases = Array.isArray(doc?.phases) ? doc.phases : [];
+  for (const phase of phases) {
+    if (!phase || typeof phase !== 'object') continue;
+    const phaseId = phase.id;
+    if (!phaseId) continue;
+    const steps = Array.isArray(phase.steps) ? phase.steps : [];
+    for (const step of steps) {
+      if (!step || typeof step !== 'object') continue;
+      const stepId = step.id;
+      if (!stepId) continue;
+      const schemaRef = step.response_schema_ref;
+      const sampleResponse = step.sample_response;
+      if (!schemaRef || !sampleResponse || typeof sampleResponse !== 'object') continue;
+      if (schemaRef.startsWith('$test_kit.')) {
+        skips++;
+        continue;
+      }
+      const result = await validateStep({ schemaRef, payload: sampleResponse });
+      if (!result.ok) {
+        violations.push({ file, phaseId, stepId, schemaRef, errors: result.errors });
+      }
+    }
+  }
+  return { violations, skips };
+}
+
+async function lintAll() {
+  const files = walkYaml(STORYBOARD_DIR);
+  const violations = [];
+  const parseErrors = [];
+  let skips = 0;
+  for (const file of files) {
+    const r = await lintFile(file);
+    if (r.parseError) parseErrors.push({ file, error: r.parseError });
+    violations.push(...r.violations);
+    skips += r.skips;
+  }
+  return { violations, parseErrors, skips };
+}
+
+function formatViolation(v) {
+  const rel = path.relative(STORYBOARD_DIR, v.file);
+  const head = `  ${rel} :: ${v.phaseId}/${v.stepId} (schema: ${v.schemaRef})`;
+  if (v.error) return `${head}\n    ERROR: ${v.error}`;
+  const errs = (v.errors || [])
+    .slice(0, 5)
+    .map((e) => `    ${e.path || '/'} [${e.keyword}] ${e.message}${e.params ? ' ' + JSON.stringify(e.params) : ''}`)
+    .join('\n');
+  const more = v.errors && v.errors.length > 5 ? `\n    … and ${v.errors.length - 5} more` : '';
+  return `${head}\n${errs}${more}`;
+}
+
+function serializeDetail(v) {
+  if (v === null || typeof v !== 'object') return String(v);
+  try {
+    return JSON.stringify(v);
+  } catch {
+    return '<unserializable>';
+  }
+}
+
+function fingerprintError(err) {
+  const path_ = err.path || '/';
+  const kw = err.keyword;
+  let detail = '';
+  if (err.params && typeof err.params === 'object') {
+    if (err.params.missingProperty) detail = `:${err.params.missingProperty}`;
+    else if (err.params.additionalProperty) detail = `:${err.params.additionalProperty}`;
+    else if (typeof err.params.allowedValue !== 'undefined') detail = `:${serializeDetail(err.params.allowedValue)}`;
+    else if (typeof err.params.type !== 'undefined') detail = `:${err.params.type}`;
+    else if (typeof err.params.format !== 'undefined') detail = `:${err.params.format}`;
+    else if (typeof err.params.limit !== 'undefined') detail = `:${err.params.limit}`;
+  }
+  return `${kw}@${path_}${detail}`;
+}
+
+function entryKey(file, phaseId, stepId) {
+  const rel = path.relative(STORYBOARD_DIR, file);
+  return `${rel}#${phaseId}/${stepId}`;
+}
+
+function loadAllowlist() {
+  if (!fs.existsSync(ALLOWLIST_PATH)) return { entries: {} };
+  try {
+    return JSON.parse(fs.readFileSync(ALLOWLIST_PATH, 'utf8'));
+  } catch (err) {
+    throw new Error(`Failed to parse allowlist at ${ALLOWLIST_PATH}: ${err.message}`);
+  }
+}
+
+function reconcileAgainstAllowlist(violations, allowlist) {
+  const entries = allowlist.entries || {};
+  const seen = new Set();
+  const newDrift = [];
+  const grandfathered = [];
+  for (const v of violations) {
+    const key = entryKey(v.file, v.phaseId, v.stepId);
+    const entry = entries[key];
+    if (!entry) {
+      newDrift.push(v);
+      continue;
+    }
+    seen.add(key);
+    const allowed = new Set(entry.errors || []);
+    const current = (v.errors || []).map(fingerprintError);
+    const unexpected = current.filter((fp) => !allowed.has(fp));
+    if (unexpected.length > 0) {
+      newDrift.push({
+        ...v,
+        errors: (v.errors || []).filter((e) => !allowed.has(fingerprintError(e))),
+      });
+    } else {
+      grandfathered.push(v);
+    }
+  }
+  const stale = [];
+  for (const [key, entry] of Object.entries(entries)) {
+    if (seen.has(key)) continue;
+    stale.push({ key, entry });
+  }
+  return { newDrift, stale, grandfathered };
+}
+
+function violationsToAllowlist(violations) {
+  const entries = {};
+  for (const v of violations) {
+    const key = entryKey(v.file, v.phaseId, v.stepId);
+    const errors = (v.errors || []).map(fingerprintError);
+    entries[key] = { schema: v.schemaRef, errors };
+  }
+  return entries;
+}
+
+function sortEntries(entries) {
+  const out = {};
+  for (const k of Object.keys(entries).sort()) out[k] = entries[k];
+  return out;
+}
+
+async function main() {
+  const args = new Set(process.argv.slice(2));
+  const { violations, parseErrors, skips } = await lintAll();
+
+  if (args.has('--write-allowlist')) {
+    if (parseErrors.length > 0) {
+      console.error(`Refusing to regenerate allowlist while ${parseErrors.length} file(s) have YAML parse errors — fix those first:`);
+      for (const p of parseErrors) console.error(`  ${path.relative(STORYBOARD_DIR, p.file)}: ${p.error}`);
+      process.exit(1);
+    }
+    const existing = loadAllowlist();
+    const nextEntries = violationsToAllowlist(violations);
+    const existingEntries = existing.entries || {};
+    if (!args.has('--allow-grow')) {
+      const added = Object.keys(nextEntries).filter((k) => !(k in existingEntries));
+      const grew = Object.keys(nextEntries).some((k) => {
+        if (!(k in existingEntries)) return false;
+        const cur = new Set(nextEntries[k].errors || []);
+        const prev = new Set(existingEntries[k].errors || []);
+        for (const fp of cur) if (!prev.has(fp)) return true;
+        return false;
+      });
+      if (added.length > 0 || grew) {
+        console.error('Refusing to grow the allowlist. Pass --allow-grow if this is intentional.');
+        if (added.length > 0) {
+          console.error('New entries:');
+          for (const k of added) console.error(`  ${k}`);
+        }
+        if (grew) console.error('At least one existing entry gained a new error fingerprint.');
+        process.exit(1);
+      }
+    }
+    const doc = {
+      $comment: [
+        'Known storyboard sample_response schema drift. Regenerate with',
+        '`node scripts/lint-storyboard-response-schema.cjs --write-allowlist`',
+        'after a real fix — defaults to shrink-only.',
+      ].join(' '),
+      entries: sortEntries(nextEntries),
+    };
+    fs.writeFileSync(ALLOWLIST_PATH, JSON.stringify(doc, null, 2) + '\n');
+    console.log(`Wrote ${Object.keys(nextEntries).length} entries to ${path.relative(process.cwd(), ALLOWLIST_PATH)}`);
+    process.exit(0);
+  }
+
+  const allowlist = loadAllowlist();
+  const { newDrift, stale, grandfathered } = reconcileAgainstAllowlist(violations, allowlist);
+
+  const hasFailure = newDrift.length > 0 || stale.length > 0 || parseErrors.length > 0;
+  if (!hasFailure) {
+    const parts = [];
+    if (grandfathered.length > 0) parts.push(`${grandfathered.length} grandfathered`);
+    if (skips > 0) parts.push(`${skips} skipped ($test_kit.)`);
+    const suffix = parts.length > 0 ? ` (${parts.join(', ')})` : '';
+    console.log(`✅ sample_response schema lint: no new drift${suffix}`);
+    process.exit(0);
+  }
+
+  if (parseErrors.length > 0) {
+    console.log(`❌ sample_response schema lint: ${parseErrors.length} file(s) have YAML parse errors\n`);
+    for (const p of parseErrors) console.log(`  ${path.relative(STORYBOARD_DIR, p.file)}: ${p.error}`);
+  }
+  if (newDrift.length > 0) {
+    console.log(`\n❌ sample_response schema lint: ${newDrift.length} step(s) have new drift\n`);
+    for (const v of newDrift) console.log(formatViolation(v));
+  }
+  if (stale.length > 0) {
+    console.log(`\n❌ sample_response schema lint: ${stale.length} stale allowlist entr${stale.length === 1 ? 'y' : 'ies'} (drift was fixed — remove from allowlist)\n`);
+    for (const s of stale) console.log(`  ${s.key}`);
+  }
+  process.exit(1);
+}
+
+if (require.main === module) main();
+
+module.exports = {
+  lintAll,
+  lintFile,
+  validateStep,
+  loadSchema,
+  formatViolation,
+  fingerprintError,
+  entryKey,
+  loadAllowlist,
+  reconcileAgainstAllowlist,
+  violationsToAllowlist,
+  sortEntries,
+  STORYBOARD_DIR,
+  ALLOWLIST_PATH,
+};
diff --git a/tests/lint-storyboard-response-schema.test.cjs b/tests/lint-storyboard-response-schema.test.cjs
new file mode 100644
index 0000000000..7a5d9e9b08
--- /dev/null
+++ b/tests/lint-storyboard-response-schema.test.cjs
@@ -0,0 +1,158 @@
+#!/usr/bin/env node
+/**
+ * Wrapper for the storyboard sample_response schema lint. Fails CI on any
+ * new drift beyond the known-issues allowlist or on stale entries that
+ * were never removed after a fix.
+ */
+
+'use strict';
+
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+
+const path = require('node:path');
+
+const {
+  lintAll,
+  loadAllowlist,
+  reconcileAgainstAllowlist,
+  validateStep,
+  fingerprintError,
+  formatViolation,
+  entryKey,
+  STORYBOARD_DIR,
+} = require('../scripts/lint-storyboard-response-schema.cjs');
+
+test('no storyboard YAML parse errors', async () => {
+  const { parseErrors } = await lintAll();
+  if (parseErrors.length > 0) {
+    const rendered = parseErrors.map((p) => `  ${p.file}: ${p.error}`).join('\n');
+    assert.fail(
+      `${parseErrors.length} storyboard file(s) failed to parse. Fix the YAML before running lint:\n${rendered}`,
+    );
+  }
+});
+
+test('no new sample_response schema drift beyond the allowlist', async () => {
+  const { violations } = await lintAll();
+  const allowlist = loadAllowlist();
+  const { newDrift } = reconcileAgainstAllowlist(violations, allowlist);
+  if (newDrift.length > 0) {
+    const rendered = newDrift.map(formatViolation).join('\n');
+    assert.fail(
+      `${newDrift.length} step(s) have sample_response schema drift that is not in the allowlist.\n` +
+        'Fix the fixture to match the schema, or (rarely) regenerate the allowlist if the drift is deliberate and pending a fix:\n' +
+        '  node scripts/lint-storyboard-response-schema.cjs --write-allowlist\n\n' +
+        rendered,
+    );
+  }
+});
+
+test('allowlist has no stale entries', async () => {
+  const { violations } = await lintAll();
+  const allowlist = loadAllowlist();
+  const { stale } = reconcileAgainstAllowlist(violations, allowlist);
+  if (stale.length > 0) {
+    const rendered = stale.map((s) => `  ${s.key}`).join('\n');
+    assert.fail(
+      `${stale.length} allowlist entr${stale.length === 1 ? 'y is' : 'ies are'} stale — the drift was fixed but the entry was not removed.\n` +
+        'Regenerate the allowlist:\n' +
+        '  node scripts/lint-storyboard-response-schema.cjs --write-allowlist\n\n' +
+        rendered,
+    );
+  }
+});
+
+test('validateStep: schema_not_found is a hard fail, not a soft skip', async () => {
+  const result = await validateStep({ schemaRef: 'does/not/exist.json', payload: {} });
+  assert.equal(result.ok, false, 'schema_not_found must not be ok:true');
+  assert.equal(result.errors.length, 1);
+  assert.equal(result.errors[0].keyword, 'schema_not_found');
+});
+
+test('fingerprintError produces stable output for common error shapes', () => {
+  assert.equal(
+    fingerprintError({ keyword: 'required', path: '/', params: { missingProperty: 'creatives' } }),
+    'required@/:creatives',
+  );
+  assert.equal(
+    fingerprintError({ keyword: 'additionalProperties', path: '/pagination', params: { additionalProperty: 'next_token' } }),
+    'additionalProperties@/pagination:next_token',
+  );
+  assert.equal(
+    fingerprintError({ keyword: 'type', path: '/pagination/has_more', params: { type: 'boolean' } }),
+    'type@/pagination/has_more:boolean',
+  );
+  assert.equal(
+    fingerprintError({ keyword: 'const', path: '/status', params: { allowedValue: 'approved' } }),
+    'const@/status:approved',
+  );
+  assert.equal(
+    fingerprintError({ keyword: 'const', path: '/shape', params: { allowedValue: { type: 'object' } } }),
+    'const@/shape:{"type":"object"}',
+  );
+});
+
+// Direct unit tests for the ratchet reducer. The end-to-end tests above prove
+// the current tree is clean; these prove the classification logic is honest
+// regardless of what the tree happens to contain.
+test('reconcileAgainstAllowlist classifies new drift, grandfathered, and stale correctly', () => {
+  const file = path.join(STORYBOARD_DIR, 'fixture.yaml');
+  const grandfatheredViolation = {
+    file,
+    phaseId: 'phase_a',
+    stepId: 'step_grandfathered',
+    schemaRef: 'x/y.json',
+    errors: [{ path: '/', keyword: 'required', params: { missingProperty: 'creatives' } }],
+  };
+  const newDriftViolation = {
+    file,
+    phaseId: 'phase_a',
+    stepId: 'step_new',
+    schemaRef: 'x/y.json',
+    errors: [{ path: '/', keyword: 'required', params: { missingProperty: 'creatives' } }],
+  };
+  const grandfatheredPlusNew = {
+    file,
+    phaseId: 'phase_b',
+    stepId: 'step_mixed',
+    schemaRef: 'x/y.json',
+    errors: [
+      { path: '/', keyword: 'required', params: { missingProperty: 'creatives' } },
+      { path: '/', keyword: 'additionalProperties', params: { additionalProperty: 'bogus' } },
+    ],
+  };
+
+  const allowlist = {
+    entries: {
+      [entryKey(file, 'phase_a', 'step_grandfathered')]: {
+        schema: 'x/y.json',
+        errors: ['required@/:creatives'],
+      },
+      [entryKey(file, 'phase_b', 'step_mixed')]: {
+        schema: 'x/y.json',
+        errors: ['required@/:creatives'],
+      },
+      [entryKey(file, 'phase_a', 'step_fixed_but_listed')]: {
+        schema: 'x/y.json',
+        errors: ['required@/:something'],
+      },
+    },
+  };
+
+  const { newDrift, stale, grandfathered } = reconcileAgainstAllowlist(
+    [grandfatheredViolation, newDriftViolation, grandfatheredPlusNew],
+    allowlist,
+  );
+
+  assert.equal(grandfathered.length, 1, 'pure grandfathered violation classified');
+  assert.equal(newDrift.length, 2, 'brand-new step and new error on listed step both count as drift');
+  const newDriftSteps = newDrift.map((v) => v.stepId).sort();
+  assert.deepEqual(newDriftSteps, ['step_mixed', 'step_new']);
+  const mixedOnly = newDrift.find((v) => v.stepId === 'step_mixed');
+  assert.equal(mixedOnly.errors.length, 1, 'only the unexpected error is kept on a mixed step');
+  assert.equal(mixedOnly.errors[0].keyword, 'additionalProperties');
+
+  assert.equal(stale.length, 1, 'allowlist entry with no matching violation is stale');
+  assert.ok(stale[0].key.endsWith('#phase_a/step_fixed_but_listed'));
+});
diff --git a/tests/storyboard-response-schema-allowlist.json b/tests/storyboard-response-schema-allowlist.json
new file mode 100644
index 0000000000..b9802691cf
--- /dev/null
+++ b/tests/storyboard-response-schema-allowlist.json
@@ -0,0 +1,4 @@
+{
+  "$comment": "Known storyboard sample_response schema drift. Regenerate with `node scripts/lint-storyboard-response-schema.cjs --write-allowlist` after a real fix — defaults to shrink-only.",
+  "entries": {}
+}