diff --git a/docs/decisions/0017-performance-budgets-lighthouse-ci.md b/docs/decisions/0017-performance-budgets-lighthouse-ci.md
index 0508e32..5c45158 100644
--- a/docs/decisions/0017-performance-budgets-lighthouse-ci.md
+++ b/docs/decisions/0017-performance-budgets-lighthouse-ci.md
@@ -209,7 +209,8 @@ No browser-side RUM SDK in v1. The OTel browser tracing from [ADR-0012](0012-obs
 ### Confirmation
 
 - `lighthouserc.js` exists at the repo root with the critical-routes list, the assertions matching the thresholds above, and a 3-iteration median configuration.
-- `apps/portal-shell/project.json` declares `budgets` with `maximumWarning == maximumError` (so an overshoot fails the build, matching `type: "error"` in spirit). Four entries: `initial` (≤ 1 MB raw), `anyScript` (≤ 300 KB raw), `anyComponentStyle` (≤ 6 KB raw, with 5 KB warning floor), `bundle name=styles` (≤ 150 KB raw). Angular CLI compares **raw** sizes; the values above are translated from the gzip-based ADR targets at the conventional ≈ 3× JS / ≈ 4× CSS compression ratios. A future follow-up will add a CI check that asserts the **actual** gzipped transfer size against the ADR thresholds — Angular CLI does not natively support a gzip-mode budget.
+- `apps/portal-shell/project.json` declares `budgets` with `maximumWarning == maximumError` (so an overshoot fails the build, matching `type: "error"` in spirit). Four entries: `initial` (≤ 1 MB raw), `anyScript` (≤ 300 KB raw), `anyComponentStyle` (≤ 6 KB raw, with 5 KB warning floor), `bundle name=styles` (≤ 150 KB raw). Angular CLI compares **raw** sizes; the values above are translated from the gzip-based ADR targets at the conventional ≈ 3× JS / ≈ 4× CSS compression ratios.
+- A complementary CI check in [`scripts/check-gzip-budgets.mjs`](../../scripts/check-gzip-budgets.mjs) (wired into `pnpm ci:perf` between the production build and Lighthouse) asserts the **actual** gzipped transfer size against the ADR thresholds: initial-JS-total ≤ 300 KB, any single lazy chunk ≤ 100 KB, total CSS ≤ 150 KB. Angular CLI does not natively support a gzip-mode budget — this script is the explicit gate. It parses `index.html` to distinguish initial assets from lazy chunks, gzips each file at level 9 (matching what HTTP servers typically serve), and exits non-zero on any breach. The check is **per locale bundle** — `@angular/localize` (per [ADR-0019](0019-internationalisation-angular-localize.md)) emits one self-contained bundle under `dist/.../browser/<locale>/`, and each is what the user's browser actually downloads, so each is checked against the same budget independently. The script auto-detects locale-split vs flat layouts.
 - `package.json` exposes `ci:perf`, runnable locally with the same exit code as CI.
 - CI's `perf` gate from [ADR-0015](0015-cicd-gitea-actions.md) calls `pnpm ci:perf`. It is blocking on human PRs and on `push` to `main`; skipped on PRs authored by the Renovate bot user (`apf-portal-bot`) per the gating-policy subsection above.
 - `apps/portal-shell` exposes a Nx target `analyze` invoking `source-map-explorer` against the production build's source maps.
diff --git a/package.json b/package.json
index 152720a..d40b049 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,8 @@
     "ci:check": "pnpm exec nx affected -t format:check lint test build",
     "ci:audit": "pnpm audit --audit-level=moderate",
     "ci:commits": "pnpm exec commitlint --from ${COMMIT_LINT_FROM:-origin/main} --to HEAD --verbose",
-    "ci:perf": "pnpm exec nx build portal-shell --configuration=production && pnpm exec lhci autorun --config=./lighthouserc.js"
+    "ci:gzip-budgets": "node scripts/check-gzip-budgets.mjs",
+    "ci:perf": "pnpm exec nx build portal-shell --configuration=production && pnpm ci:gzip-budgets && pnpm exec lhci autorun --config=./lighthouserc.js"
   },
   "private": true,
   "lint-staged": {
diff --git a/scripts/check-gzip-budgets.mjs b/scripts/check-gzip-budgets.mjs
new file mode 100644
index 0000000..b0b8e06
--- /dev/null
+++ b/scripts/check-gzip-budgets.mjs
@@ -0,0 +1,229 @@
+#!/usr/bin/env node
+/**
+ * Check the gzip-transfer size of an Angular production build against
+ * the ADR-0017 perf budgets. Complements Angular CLI's native
+ * `budgets` (which only compare RAW sizes — no built-in gzip mode).
+ *
+ * Strategy
+ * --------
+ * 1. Parse the Angular `index.html` of the build output. Every
+ *    `<script src="…">` and `<link href="…">` referencing a JS/CSS
+ *    asset is part of the **initial** payload. Everything else in
+ *    the output dir is a **lazy** chunk loaded on demand.
+ * 2. Gzip every JS/CSS file with level 9 (matching what HTTP
+ *    servers typically emit for static assets) and report the
+ *    resulting transfer size.
+ * 3. Compare:
+ *    - sum of initial JS  ≤ BUDGET_INITIAL_JS_TOTAL
+ *    - any single lazy JS ≤ BUDGET_LAZY_JS_EACH
+ *    - sum of all CSS     ≤ BUDGET_CSS_TOTAL
+ *    Exit non-zero on any violation.
+ *
+ * Locale-split builds (ADR-0019)
+ * ------------------------------
+ * `@angular/localize` emits one self-contained bundle per locale under
+ * `dist/apps/portal-shell/browser/<locale>/`. The script auto-detects
+ * the layout: if the root has no `index.html` but immediate
+ * subdirectories do, each subdirectory is checked against the budgets
+ * separately. Budget thresholds apply *per locale* — each bundle is
+ * what the user's browser actually downloads. Violations across
+ * locales are aggregated and reported together so a single CI run
+ * surfaces every breach.
+ *
+ * Invocation: `node scripts/check-gzip-budgets.mjs [dist-dir]`.
+ * The default `dist-dir` is `dist/apps/portal-shell/browser`.
+ */
+
+import { readdir, readFile, stat } from 'node:fs/promises';
+import { gzipSync } from 'node:zlib';
+import { basename, join } from 'node:path';
+
+const DEFAULT_DIST = 'dist/apps/portal-shell/browser';
+const dist = process.argv[2] ?? DEFAULT_DIST;
+
+// ADR-0017 budgets (gzip transfer, in bytes).
+const BUDGET_INITIAL_JS_TOTAL = 300 * 1024;
+const BUDGET_LAZY_JS_EACH = 100 * 1024;
+const BUDGET_CSS_TOTAL = 150 * 1024;
+
+const fmtKb = (n) => `${(n / 1024).toFixed(2)} KB`;
+const padFile = (s) => s.padEnd(36);
+
+async function gzipSize(path) {
+  return gzipSync(await readFile(path), { level: 9 }).byteLength;
+}
+
+async function fileExists(path) {
+  try {
+    await stat(path);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Check one Angular build directory (a single `index.html` and its
+ * sibling JS/CSS assets) against the ADR-0017 budgets. Returns the
+ * violations found — empty array means the bundle passed.
+ *
+ * The header passed in is rendered above the per-file table so the
+ * multi-locale invocation can prefix each section with the locale
+ * tag.
+ */
+async function checkBundle(bundleDir, header) {
+  let indexHtml;
+  try {
+    indexHtml = await readFile(join(bundleDir, 'index.html'), 'utf8');
+  } catch (err) {
+    throw new Error(`could not read ${join(bundleDir, 'index.html')}: ${err.message}`);
+  }
+
+  // Match every src=/href= that points at a .js or .css file in the
+  // output dir. Robust enough for Angular's emitted index.html (which
+  // is well-formed and predictable).
+  const referenced = new Set(
+    [...indexHtml.matchAll(/(?:src|href)\s*=\s*["']([^"']+\.(?:js|css))["']/g)].map((m) =>
+      basename(m[1]),
+    ),
+  );
+
+  const all = await readdir(bundleDir);
+  const jsFiles = all.filter((f) => f.endsWith('.js'));
+  const cssFiles = all.filter((f) => f.endsWith('.css'));
+
+  const initialJs = jsFiles.filter((f) => referenced.has(f));
+  const lazyJs = jsFiles.filter((f) => !referenced.has(f));
+
+  const sized = async (files) =>
+    Promise.all(files.map(async (f) => ({ f, size: await gzipSize(join(bundleDir, f)) })));
+
+  const initialJsSizes = await sized(initialJs);
+  const lazyJsSizes = await sized(lazyJs);
+  const cssSizes = await sized(cssFiles);
+
+  const sum = (arr) => arr.reduce((s, x) => s + x.size, 0);
+  const totalInitialJs = sum(initialJsSizes);
+  const totalCss = sum(cssSizes);
+
+  const violations = [];
+
+  console.log(header);
+
+  console.log('  Initial JS (loaded on first paint):');
+  for (const { f, size } of initialJsSizes.sort((a, b) => b.size - a.size)) {
+    console.log(`    ${padFile(f)} ${fmtKb(size)}`);
+  }
+  const initialFlag = totalInitialJs > BUDGET_INITIAL_JS_TOTAL ? ' ✗ EXCEEDS BUDGET' : ' ✓';
+  console.log(
+    `    ${padFile('TOTAL')} ${fmtKb(totalInitialJs)} / ${fmtKb(BUDGET_INITIAL_JS_TOTAL)}${initialFlag}`,
+  );
+  if (totalInitialJs > BUDGET_INITIAL_JS_TOTAL) {
+    violations.push(
+      `${header.trim()}: initial JS total ${fmtKb(totalInitialJs)} > budget ${fmtKb(BUDGET_INITIAL_JS_TOTAL)}`,
+    );
+  }
+
+  console.log('\n  Lazy JS chunks (loaded on demand):');
+  if (lazyJsSizes.length === 0) {
+    console.log('    (none)');
+  }
+  for (const { f, size } of lazyJsSizes.sort((a, b) => b.size - a.size)) {
+    const flag = size > BUDGET_LAZY_JS_EACH ? ' ✗ EXCEEDS BUDGET' : '';
+    console.log(`    ${padFile(f)} ${fmtKb(size)}${flag}`);
+    if (size > BUDGET_LAZY_JS_EACH) {
+      violations.push(
+        `${header.trim()}: lazy chunk ${f} ${fmtKb(size)} > per-chunk budget ${fmtKb(BUDGET_LAZY_JS_EACH)}`,
+      );
+    }
+  }
+  console.log(`    (per-chunk budget: ${fmtKb(BUDGET_LAZY_JS_EACH)})`);
+
+  console.log('\n  CSS files:');
+  for (const { f, size } of cssSizes.sort((a, b) => b.size - a.size)) {
+    console.log(`    ${padFile(f)} ${fmtKb(size)}`);
+  }
+  const cssFlag = totalCss > BUDGET_CSS_TOTAL ? ' ✗ EXCEEDS BUDGET' : ' ✓';
+  console.log(
+    `    ${padFile('TOTAL')} ${fmtKb(totalCss)} / ${fmtKb(BUDGET_CSS_TOTAL)}${cssFlag}\n`,
+  );
+  if (totalCss > BUDGET_CSS_TOTAL) {
+    violations.push(
+      `${header.trim()}: CSS total ${fmtKb(totalCss)} > budget ${fmtKb(BUDGET_CSS_TOTAL)}`,
+    );
+  }
+
+  return violations;
+}
+
+/**
+ * Resolve which directories to check. A locale-split build has no
+ * `index.html` at the root but does have one in each immediate
+ * subdirectory (ADR-0019 §"`@angular/localize` build-time mode").
+ * Returns either `[dist]` (flat layout) or `[dist/fr, dist/en, …]`
+ * (locale split, sorted alphabetically for deterministic output).
+ */
+async function resolveBundles(root) {
+  if (await fileExists(join(root, 'index.html'))) {
+    return [{ dir: root, label: root }];
+  }
+  let entries;
+  try {
+    entries = await readdir(root, { withFileTypes: true });
+  } catch (err) {
+    throw new Error(`could not read ${root}: ${err.message}`);
+  }
+  const subdirsWithIndex = [];
+  for (const entry of entries) {
+    if (!entry.isDirectory()) continue;
+    const candidate = join(root, entry.name);
+    if (await fileExists(join(candidate, 'index.html'))) {
+      subdirsWithIndex.push({ dir: candidate, label: entry.name });
+    }
+  }
+  if (subdirsWithIndex.length === 0) {
+    throw new Error(
+      `no index.html in ${root} and no locale subdirectory contains one — ` +
+        `did you run "nx build portal-shell --configuration=production" first?`,
+    );
+  }
+  subdirsWithIndex.sort((a, b) => a.label.localeCompare(b.label));
+  return subdirsWithIndex;
+}
+
+async function main() {
+  let bundles;
+  try {
+    bundles = await resolveBundles(dist);
+  } catch (err) {
+    console.error(`✗ ${err.message}`);
+    process.exit(2);
+  }
+
+  const multi = bundles.length > 1;
+  console.log(
+    `Gzip-transfer budget check (ADR-0017) — output: ${dist}` +
+      (multi ? ` (${bundles.length} locale bundles)` : '') +
+      '\n',
+  );
+
+  const violations = [];
+  for (const { dir, label } of bundles) {
+    const header = multi ? `[locale: ${label}]\n` : '';
+    const found = await checkBundle(dir, header);
+    violations.push(...found);
+  }
+
+  if (violations.length > 0) {
+    console.error('✗ ADR-0017 budget violations:');
+    for (const v of violations) console.error(`  - ${v}`);
+    process.exit(1);
+  }
+
+  console.log('✓ All ADR-0017 gzip-transfer budgets respected.');
+}
+
+main().catch((err) => {
+  console.error('Budget check failed:', err);
+  process.exit(2);
+});