ci(i18n): fail on new English-identical translations

The drift check only warned about locale values identical to English, so
untranslated strings kept landing. It now fails on any such value that
tools/i18n/identical-en-baseline.json does not record for that locale and
key. The baseline captures today's 2,015 entries: legitimately identical
values (brand and technical names, language autonyms, PIN) and the
existing debt. An entry only covers the English text it recorded, so
copying reworded English into a locale fails too.

Baseline entries that are no longer identical are reported, not fatal.
`pnpm run i18n:baseline:update` rewrites the baseline deliberately; CI
runs `pnpm run i18n:validate` (node tests, then the check) and never
rewrites it. `--fail-on-identical` remains as a strict audit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -390,8 +390,12 @@ jobs:
             - name: Typecheck Jest spec programs
               run: pnpm run typecheck:spec:test && pnpm run typecheck:spec
 
-            - name: Check i18n drift
-              run: pnpm run i18n:check
+            # Fails on missing or extra keys and on values identical to
+            # English that tools/i18n/identical-en-baseline.json does not list.
+            # The baseline only changes through a reviewed
+            # `pnpm run i18n:baseline:update`; CI never rewrites it.
+            - name: Check i18n drift and untranslated values
+              run: pnpm run i18n:validate
 
             # Node specs for the benchmark and journey harness (about ten
             # seconds). They live in the E2E app, which the unit coverage scope

docs/architecture/validation-map.md

@@ -242,14 +242,31 @@ pnpm run coverage:e2e:v8:web
 ## I18n
 
 ```bash
-pnpm run i18n:check
+pnpm run i18n:validate          # checker unit tests, then the check (CI)
+pnpm run i18n:check             # the check only
+pnpm run i18n:baseline:update   # deliberate: rewrite the English-identical baseline
 ```
 
 The i18n check is non-mutating. It compares every locale file in
 `apps/web/src/assets/i18n/` against `en.json` and fails on missing or extra keys.
-Identical English fallback values are reported as warnings by default; use
-`node tools/i18n/check-drift.mjs --fail-on-identical` for a stricter translation
-audit.
+It also fails on a locale value that is identical to English unless
+`tools/i18n/identical-en-baseline.json` records that exact English text for the
+same locale and key. The baseline holds values that are legitimately the same
+in a language (brand and technical names, language autonyms, loanwords such as
+"PIN") and the untranslated debt that existed when the guard was added, so new
+keys must ship translated. An entry stops covering its key once the English
+text changes, so copying reworded English into a locale fails as well.
+
+Baseline entries that are no longer English-identical (translated, removed, or
+reworded) are reported but do not fail. `pnpm run i18n:baseline:update`
+rewrites the baseline from the current locale files, dropping those entries
+and printing every added one. Run it only after translating, or for a value
+that is legitimately identical in that language; review the diff, and never
+run it in CI. A new locale starts with no baseline entries, so it has to
+record its legitimate identical values the same way.
+`node tools/i18n/check-drift.mjs --fail-on-identical` ignores the baseline for
+a full translation audit. CI runs `pnpm run i18n:validate` in the unit test
+job.
 
 ## Performance
 

package.json

@@ -79,6 +79,9 @@
         "serve:website": "nx serve website",
         "build:website": "nx build website",
         "i18n:check": "node tools/i18n/check-drift.mjs",
+        "i18n:test": "node --test tools/i18n/check-drift.test.mjs",
+        "i18n:validate": "pnpm run i18n:test && pnpm run i18n:check",
+        "i18n:baseline:update": "node tools/i18n/check-drift.mjs --update-baseline",
         "perf:initial-bytes": "node tools/performance/measure-initial-bytes.mjs",
         "perf:initial-bytes:check": "node tools/performance/measure-initial-bytes.mjs --summary dist/performance/initial-bytes.summary.json && node tools/performance/check-journey-ratchet.mjs --summary dist/performance/initial-bytes.summary.json --only launch/renderer.initialBytes",
         "perf:journeys": "nx run electron-backend-e2e:journeys",

tools/i18n/README.md

@@ -49,10 +49,24 @@ For a non-mutating CI/agent check, run:
 pnpm run i18n:check
 ```
 
-The check fails on missing or extra keys against `en.json`. It reports values
-that are still identical to English as warnings so untranslated fallback strings
-remain visible without blocking key-parity validation. For stricter translation
-audits, run:
+The check fails on missing or extra keys against `en.json`, and on values that
+are identical to English unless `identical-en-baseline.json` lists that exact
+English text for the locale and key. Do not copy English into a locale as a
+placeholder: translate it. The contract, including when an entry stops
+covering a key, is in the
+[validation map](../../docs/architecture/validation-map.md#i18n).
+
+Baseline entries that are no longer identical are reported, not fatal. After
+translating baselined values, or for a value that is legitimately the same in a
+language (a brand, a technical name, a loanword), rewrite the baseline and
+review every added entry in the diff:
+
+```bash
+pnpm run i18n:baseline:update
+```
+
+The checker's own tests run with `pnpm run i18n:test`; CI runs both through
+`pnpm run i18n:validate`. For a full audit that ignores the baseline, run:
 
 ```bash
 node tools/i18n/check-drift.mjs --fail-on-identical

tools/i18n/check-drift.mjs

@@ -1,27 +1,47 @@
 #!/usr/bin/env node
-import { readdirSync, readFileSync } from 'node:fs';
+/**
+ * Compares every locale in apps/web/src/assets/i18n/ with en.json.
+ *
+ * Missing or extra keys fail. A value identical to English fails too, unless
+ * tools/i18n/identical-en-baseline.json records that exact English text for
+ * that locale and key. The baseline holds values that are legitimately the
+ * same in a language (brands, technical terms, loanwords such as "PIN") and
+ * the untranslated debt that existed when the guard was introduced, so new
+ * keys must ship translated while old debt can be paid down.
+ *
+ * Baseline entries that no longer match an English-identical value are only
+ * reported. `--update-baseline` rewrites the baseline from the current files;
+ * run it deliberately and review the diff. CI never runs it.
+ * `--fail-on-identical` ignores the baseline for a strict audit.
+ */
+import { readdirSync, readFileSync, writeFileSync } from 'node:fs';
 import { dirname, resolve } from 'node:path';
 import { fileURLToPath } from 'node:url';
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
-const REPO_ROOT = resolve(__dirname, '..', '..');
-const I18N_DIR = resolve(REPO_ROOT, 'apps/web/src/assets/i18n');
-const EN_LOCALE = 'en.json';
+export const I18N_DIR = resolve(__dirname, '../../apps/web/src/assets/i18n');
+export const BASELINE_PATH = resolve(__dirname, 'identical-en-baseline.json');
+const EN_LOCALE = 'en';
 const MAX_EXAMPLES = 5;
-const FAIL_ON_IDENTICAL = process.argv.includes('--fail-on-identical');
+const UPDATE_COMMAND = 'pnpm run i18n:baseline:update';
+const FLAGS = new Set(['--fail-on-identical', '--update-baseline', '--']);
 
 function readJson(filePath) {
     return JSON.parse(readFileSync(filePath, 'utf8'));
 }
 
-function collectLeaves(value, prefix = '', leaves = new Map()) {
-    if (!value || typeof value !== 'object' || Array.isArray(value)) {
+function isPlainObject(value) {
+    return !!value && typeof value === 'object' && !Array.isArray(value);
+}
+
+export function collectLeaves(value, prefix = '', leaves = new Map()) {
+    if (!isPlainObject(value)) {
         throw new Error(`Expected object at ${prefix || '<root>'}`);
     }
 
     for (const [key, entry] of Object.entries(value)) {
         const path = prefix ? `${prefix}.${key}` : key;
-        if (entry && typeof entry === 'object' && !Array.isArray(entry)) {
+        if (isPlainObject(entry)) {
             collectLeaves(entry, path, leaves);
         } else {
             leaves.set(path, entry);
@@ -31,10 +51,87 @@ function collectLeaves(value, prefix = '', leaves = new Map()) {
     return leaves;
 }
 
-function listLocaleFiles() {
-    return readdirSync(I18N_DIR)
-        .filter((file) => file.endsWith('.json'))
-        .sort();
+/** Keys whose non-empty locale string equals the English string. */
+export function findIdenticalToEnglish(enLeaves, localeLeaves) {
+    const identical = new Map();
+    for (const [key, enValue] of enLeaves) {
+        const localeValue = localeLeaves.get(key);
+        if (
+            typeof enValue === 'string' &&
+            localeValue === enValue &&
+            enValue.trim().length > 0
+        ) {
+            identical.set(key, enValue);
+        }
+    }
+    return identical;
+}
+
+/**
+ * Splits a locale's English-identical keys into baselined and new ones. An
+ * entry covers a key only while its recorded text is still the English text,
+ * so rewording English and copying the new text into a locale is new debt.
+ * Stale entries no longer describe an English-identical value: the key was
+ * translated or removed, or its English text changed.
+ */
+export function compareWithBaseline(identical, localeBaseline = new Map()) {
+    const baselined = [];
+    const unbaselined = [];
+    for (const [key, value] of identical) {
+        (localeBaseline.get(key) === value ? baselined : unbaselined).push(key);
+    }
+    const stale = [...localeBaseline]
+        .filter(([key, value]) => identical.get(key) !== value)
+        .map(([key]) => key);
+    return { baselined, unbaselined, stale };
+}
+
+/** Validates the baseline JSON into Map<locale, Map<key, englishText>>. */
+export function parseBaseline(raw) {
+    if (!isPlainObject(raw)) {
+        throw new Error('expected an object of locales');
+    }
+    const baseline = new Map();
+    for (const [locale, entries] of Object.entries(raw)) {
+        if (!isPlainObject(entries)) {
+            throw new Error(`expected an object of keys for ${locale}`);
+        }
+        for (const [key, value] of Object.entries(entries)) {
+            if (typeof value !== 'string') {
+                throw new Error(`expected English text at ${locale} ${key}`);
+            }
+        }
+        baseline.set(locale, new Map(Object.entries(entries)));
+    }
+    return baseline;
+}
+
+/** Serialises Map<locale, Map<key, text>> with locales and keys sorted. */
+export function serializeBaseline(identicalByLocale) {
+    const byCodeUnit = (a, b) => (a < b ? -1 : a > b ? 1 : 0);
+    const output = {};
+    for (const locale of [...identicalByLocale.keys()].sort(byCodeUnit)) {
+        const entries = identicalByLocale.get(locale);
+        if (entries.size > 0) {
+            output[locale] = Object.fromEntries(
+                [...entries].sort(([a], [b]) => byCodeUnit(a, b))
+            );
+        }
+    }
+    return `${JSON.stringify(output, null, 4)}\n`;
+}
+
+function countChanges(from, to, onChange = () => undefined) {
+    let changes = 0;
+    for (const [locale, entries] of from) {
+        for (const [key, value] of entries) {
+            if (to.get(locale)?.get(key) !== value) {
+                changes += 1;
+                onChange(locale, key, value);
+            }
+        }
+    }
+    return changes;
 }
 
 function formatExamples(values) {
@@ -50,73 +147,191 @@ function formatError(error) {
     return error instanceof Error ? error.message : String(error);
 }
 
-let enLeaves;
-try {
-    enLeaves = collectLeaves(readJson(resolve(I18N_DIR, EN_LOCALE)));
-} catch (error) {
-    console.error(`FAIL ${EN_LOCALE}: ${formatError(error)}`);
-    process.exit(1);
-}
-
-const enKeys = [...enLeaves.keys()];
-let failed = false;
-let identicalTotal = 0;
-
-for (const localeFile of listLocaleFiles()) {
-    if (localeFile === EN_LOCALE) {
-        continue;
-    }
-
+function readBaseline(baselinePath) {
+    let raw;
     try {
-        const localeLeaves = collectLeaves(
-            readJson(resolve(I18N_DIR, localeFile))
-        );
-        const localeKeys = [...localeLeaves.keys()];
-        const missing = enKeys.filter((key) => !localeLeaves.has(key));
-        const extra = localeKeys.filter((key) => !enLeaves.has(key));
-        const identical = enKeys.filter((key) => {
-            if (!localeLeaves.has(key)) {
-                return false;
-            }
-
-            const localeValue = localeLeaves.get(key);
-            const enValue = enLeaves.get(key);
-
-            return (
-                typeof localeValue === 'string' &&
-                typeof enValue === 'string' &&
-                localeValue.trim().length > 0 &&
-                localeValue === enValue
-            );
-        });
-
-        identicalTotal += identical.length;
-        const localeFailed =
-            missing.length > 0 ||
-            extra.length > 0 ||
-            (FAIL_ON_IDENTICAL && identical.length > 0);
-        failed = failed || localeFailed;
-
-        const status = localeFailed ? 'FAIL' : 'ok';
-        console.log(
-            `${status} ${localeFile}: missing=${missing.length}${formatExamples(
-                missing
-            )} extra=${extra.length}${formatExamples(extra)} identical_en=${
-                identical.length
-            }${formatExamples(identical)}`
-        );
+        raw = readJson(baselinePath);
     } catch (error) {
-        failed = true;
-        console.log(`FAIL ${localeFile}: ${formatError(error)}`);
+        if (error?.code === 'ENOENT') {
+            return new Map();
+        }
+        throw new Error(`${baselinePath}: ${formatError(error)}`);
+    }
+    try {
+        return parseBaseline(raw);
+    } catch (error) {
+        throw new Error(`${baselinePath}: ${formatError(error)}`);
     }
 }
 
-if (identicalTotal > 0 && !FAIL_ON_IDENTICAL) {
-    console.log(
-        `warn identical_en=${identicalTotal}; pass --fail-on-identical to make English fallback values fatal.`
+function listLocales(i18nDir) {
+    return readdirSync(i18nDir)
+        .filter((file) => file.endsWith('.json'))
+        .map((file) => file.slice(0, -'.json'.length))
+        .filter((locale) => locale !== EN_LOCALE)
+        .sort();
+}
+
+function checkLocale({ i18nDir, locale, enLeaves, baseline, mode }) {
+    const localeLeaves = collectLeaves(
+        readJson(resolve(i18nDir, `${locale}.json`))
+    );
+    const missing = [...enLeaves.keys()].filter(
+        (key) => !localeLeaves.has(key)
+    );
+    const extra = [...localeLeaves.keys()].filter((key) => !enLeaves.has(key));
+    const identical = findIdenticalToEnglish(enLeaves, localeLeaves);
+    const { baselined, unbaselined, stale } = compareWithBaseline(
+        identical,
+        baseline.get(locale)
+    );
+    const rejected =
+        mode === 'strict'
+            ? [...identical.keys()]
+            : mode === 'update'
+              ? []
+              : unbaselined;
+    return { missing, extra, identical, baselined, rejected, stale };
+}
+
+function reportLocale(log, file, result, mode) {
+    const { missing, extra, identical, baselined, rejected, stale } = result;
+    const failed = missing.length + extra.length + rejected.length > 0;
+    const baselineNote =
+        mode === 'baseline' ? ` baselined=${baselined.length}` : '';
+    log(
+        `${failed ? 'FAIL' : 'ok'} ${file}: missing=${
+            missing.length
+        }${formatExamples(missing)} extra=${extra.length}${formatExamples(
+            extra
+        )} identical_en=${identical.size}${baselineNote}`
+    );
+    if (mode === 'baseline' && stale.length > 0) {
+        log(
+            `note ${file}: ${stale.length} baseline entries are no longer English-identical${formatExamples(
+                stale
+            )}`
+        );
+    }
+    return failed;
+}
+
+function reportRejected(log, rejected, enLeaves, mode) {
+    if (rejected.length === 0) {
+        return;
+    }
+    const scope = mode === 'strict' ? '' : ' and are not in the baseline';
+    log(`${rejected.length} value(s) equal English${scope}:`);
+    for (const [file, key] of rejected) {
+        log(`  ${file} ${key}: ${JSON.stringify(enLeaves.get(key))}`);
+    }
+    if (mode === 'baseline') {
+        log(
+            `Translate them (see the i18n-fill skill). Only if a value is legitimately the same in that language, run \`${UPDATE_COMMAND}\` and commit the reviewed baseline.`
+        );
+    }
+}
+
+function writeBaseline(log, baselinePath, previous, identicalByLocale) {
+    const added = countChanges(
+        identicalByLocale,
+        previous,
+        (locale, key, value) =>
+            log(`  + ${locale} ${key}: ${JSON.stringify(value)}`)
+    );
+    const removed = countChanges(previous, identicalByLocale);
+    writeFileSync(baselinePath, serializeBaseline(identicalByLocale));
+    log(
+        `Baseline written: ${added} added, ${removed} removed. Review every added entry before committing.`
     );
 }
 
-if (failed) {
-    process.exitCode = 1;
+/** Runs the check and returns the process exit code. */
+export function run({
+    i18nDir = I18N_DIR,
+    baselinePath = BASELINE_PATH,
+    argv = [],
+    log = console.log,
+} = {}) {
+    const strict = argv.includes('--fail-on-identical');
+    const update = argv.includes('--update-baseline');
+    if (argv.some((arg) => !FLAGS.has(arg)) || (strict && update)) {
+        log(
+            `FAIL unsupported arguments: ${argv.join(' ')}; pass at most one of --fail-on-identical and --update-baseline.`
+        );
+        return 1;
+    }
+    const mode = strict ? 'strict' : update ? 'update' : 'baseline';
+
+    let enLeaves;
+    let baseline;
+    try {
+        enLeaves = collectLeaves(
+            readJson(resolve(i18nDir, `${EN_LOCALE}.json`))
+        );
+        baseline = readBaseline(baselinePath);
+    } catch (error) {
+        if (!enLeaves || !update) {
+            log(`FAIL ${formatError(error)}`);
+            return 1;
+        }
+        log(`note replacing unreadable baseline: ${formatError(error)}`);
+        baseline = new Map();
+    }
+
+    const locales = listLocales(i18nDir);
+    const identicalByLocale = new Map();
+    const rejected = [];
+    let failed = false;
+    let unreadable = false;
+    let staleTotal = 0;
+
+    for (const locale of locales) {
+        const file = `${locale}.json`;
+        let result;
+        try {
+            result = checkLocale({ i18nDir, locale, enLeaves, baseline, mode });
+        } catch (error) {
+            failed = unreadable = true;
+            log(`FAIL ${file}: ${formatError(error)}`);
+            continue;
+        }
+        identicalByLocale.set(locale, result.identical);
+        rejected.push(...result.rejected.map((key) => [file, key]));
+        staleTotal += result.stale.length;
+        failed = reportLocale(log, file, result, mode) || failed;
+    }
+
+    if (mode === 'baseline') {
+        for (const [locale, entries] of baseline) {
+            if (!locales.includes(locale)) {
+                staleTotal += entries.size;
+                log(`note ${locale}: baseline lists a locale with no file`);
+            }
+        }
+        if (staleTotal > 0) {
+            log(
+                `note ${staleTotal} stale baseline entries; run \`${UPDATE_COMMAND}\` to shrink the baseline.`
+            );
+        }
+    }
+    reportRejected(log, rejected, enLeaves, mode);
+
+    if (update) {
+        if (unreadable) {
+            log('FAIL baseline not written: a locale file could not be read.');
+            return 1;
+        }
+        writeBaseline(log, baselinePath, baseline, identicalByLocale);
+    }
+
+    return failed ? 1 : 0;
+}
+
+const isMain =
+    process.argv[1] &&
+    resolve(process.argv[1]) === resolve(fileURLToPath(import.meta.url));
+
+if (isMain) {
+    process.exitCode = run({ argv: process.argv.slice(2) });
 }

tools/i18n/check-drift.test.mjs

@@ -0,0 +1,248 @@
+import assert from 'node:assert/strict';
+import {
+    mkdirSync,
+    mkdtempSync,
+    readFileSync,
+    rmSync,
+    writeFileSync,
+} from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { afterEach, beforeEach, test } from 'node:test';
+
+import { parseBaseline, run, serializeBaseline } from './check-drift.mjs';
+
+const EN = {
+    APP: { TITLE: 'IPTVnator', SAVE: 'Save' },
+    PIN: 'PIN',
+};
+
+let root;
+let dir;
+let baselinePath;
+
+beforeEach(() => {
+    root = mkdtempSync(path.join(os.tmpdir(), 'i18n-drift-'));
+    dir = path.join(root, 'i18n');
+    mkdirSync(dir);
+    baselinePath = path.join(root, 'identical-en-baseline.json');
+});
+
+afterEach(() => {
+    rmSync(root, { recursive: true, force: true });
+});
+
+function writeLocale(locale, content) {
+    writeFileSync(path.join(dir, `${locale}.json`), JSON.stringify(content));
+}
+
+function writeBaseline(content) {
+    writeFileSync(baselinePath, JSON.stringify(content));
+}
+
+function check(...argv) {
+    const lines = [];
+    const code = run({
+        i18nDir: dir,
+        baselinePath,
+        argv,
+        log: (line) => lines.push(line),
+    });
+    return { code, output: lines.join('\n') };
+}
+
+function readBaselineFile() {
+    return JSON.parse(readFileSync(baselinePath, 'utf8'));
+}
+
+test('fails on a new English-identical key that the baseline does not list', () => {
+    writeLocale('en', { ...EN, APP: { ...EN.APP, NEW: 'New label' } });
+    writeLocale('de', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Speichern', NEW: 'New label' },
+        PIN: 'PIN',
+    });
+    writeBaseline({ de: { 'APP.TITLE': 'IPTVnator', PIN: 'PIN' } });
+
+    const { code, output } = check();
+
+    assert.equal(code, 1);
+    assert.match(output, /^FAIL de\.json: .*identical_en=3 baselined=2$/m);
+    assert.match(output, /de\.json APP\.NEW: "New label"/);
+});
+
+test('passes a translated key', () => {
+    writeLocale('en', EN);
+    writeLocale('de', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Speichern' },
+        PIN: 'PIN-Code',
+    });
+    writeBaseline({ de: { 'APP.TITLE': 'IPTVnator' } });
+
+    const { code, output } = check();
+
+    assert.equal(code, 0);
+    assert.match(output, /^ok de\.json: .*identical_en=1 baselined=1$/m);
+});
+
+test('passes an English-identical key listed in the baseline', () => {
+    writeLocale('en', EN);
+    writeLocale('de', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Speichern' },
+        PIN: 'PIN',
+    });
+    writeBaseline({ de: { 'APP.TITLE': 'IPTVnator', PIN: 'PIN' } });
+
+    assert.equal(check().code, 0);
+});
+
+test('a baseline entry only covers the English text it recorded', () => {
+    // English was reworded and the new text copied into the locale: that is
+    // new untranslated text, not the value the baseline accepted.
+    writeLocale('en', { ...EN, APP: { ...EN.APP, SAVE: 'Save changes' } });
+    writeLocale('de', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Save changes' },
+        PIN: 'PIN-Code',
+    });
+    writeBaseline({ de: { 'APP.TITLE': 'IPTVnator', 'APP.SAVE': 'Save' } });
+
+    const { code, output } = check();
+
+    assert.equal(code, 1);
+    assert.match(output, /de\.json APP\.SAVE: "Save changes"/);
+});
+
+test('reports baseline entries that are no longer identical without failing', () => {
+    writeLocale('en', EN);
+    writeLocale('de', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Speichern' },
+        PIN: 'PIN-Code',
+    });
+    writeBaseline({
+        de: { 'APP.TITLE': 'IPTVnator', 'APP.SAVE': 'Save', PIN: 'PIN' },
+        fr: { PIN: 'PIN' },
+    });
+
+    const { code, output } = check();
+
+    assert.equal(code, 0);
+    assert.match(
+        output,
+        /^note de\.json: 2 baseline entries .*\(APP\.SAVE, PIN\)$/m
+    );
+    assert.match(output, /^note fr: baseline lists a locale with no file$/m);
+    assert.match(
+        output,
+        /^note 3 stale baseline entries; run .*i18n:baseline:update/m
+    );
+});
+
+test('a locale without baseline entries fails on every identical value', () => {
+    writeLocale('en', EN);
+    writeLocale('uk', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Зберегти' },
+        PIN: 'PIN-код',
+    });
+
+    const { code, output } = check();
+
+    assert.equal(code, 1);
+    assert.match(output, /uk\.json APP\.TITLE: "IPTVnator"/);
+});
+
+test('still fails on missing and extra keys', () => {
+    writeLocale('en', EN);
+    writeLocale('de', { APP: { TITLE: 'IPTVnator', OLD: 'Alt' }, PIN: 'PIN' });
+    writeBaseline({ de: { 'APP.TITLE': 'IPTVnator', PIN: 'PIN' } });
+
+    const { code, output } = check();
+
+    assert.equal(code, 1);
+    assert.match(
+        output,
+        /^FAIL de\.json: missing=1 \(APP\.SAVE\) extra=1 \(APP\.OLD\)/m
+    );
+});
+
+test('--fail-on-identical ignores the baseline', () => {
+    writeLocale('en', EN);
+    writeLocale('de', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Speichern' },
+        PIN: 'PIN',
+    });
+    writeBaseline({ de: { 'APP.TITLE': 'IPTVnator', PIN: 'PIN' } });
+
+    const { code, output } = check('--fail-on-identical');
+
+    assert.equal(code, 1);
+    assert.match(output, /de\.json APP\.TITLE: "IPTVnator"/);
+    assert.match(output, /de\.json PIN: "PIN"/);
+});
+
+test('--update-baseline records current identical values and drops resolved ones', () => {
+    writeLocale('en', EN);
+    writeLocale('de', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Speichern' },
+        PIN: 'PIN',
+    });
+    writeLocale('fr', {
+        APP: { TITLE: 'IPTVnator', SAVE: 'Enregistrer' },
+        PIN: 'Code PIN',
+    });
+    writeBaseline({ de: { 'APP.SAVE': 'Save' }, fr: { PIN: 'PIN' } });
+
+    const { code, output } = check('--update-baseline');
+
+    assert.equal(code, 0);
+    assert.match(output, /^ {2}\+ de PIN: "PIN"$/m);
+    assert.match(output, /Baseline written: 3 added, 2 removed\./);
+    assert.deepEqual(readBaselineFile(), {
+        de: { 'APP.TITLE': 'IPTVnator', PIN: 'PIN' },
+        fr: { 'APP.TITLE': 'IPTVnator' },
+    });
+    assert.equal(check().code, 0);
+});
+
+test('--update-baseline keeps the old baseline when a locale is unreadable', () => {
+    writeLocale('en', EN);
+    writeFileSync(path.join(dir, 'de.json'), '{ broken');
+    writeBaseline({ de: { PIN: 'PIN' } });
+
+    const { code, output } = check('--update-baseline');
+
+    assert.equal(code, 1);
+    assert.match(output, /baseline not written/);
+    assert.deepEqual(readBaselineFile(), { de: { PIN: 'PIN' } });
+});
+
+test('rejects unknown and conflicting flags', () => {
+    writeLocale('en', EN);
+
+    assert.equal(check('--update').code, 1);
+    assert.equal(check('--fail-on-identical', '--update-baseline').code, 1);
+});
+
+test('rejects a malformed baseline', () => {
+    assert.throws(() => parseBaseline({ de: ['PIN'] }), /object of keys/);
+    assert.throws(() => parseBaseline({ de: { PIN: 1 } }), /English text/);
+});
+
+test('serialises locales and keys in a stable order', () => {
+    const serialized = serializeBaseline(
+        new Map([
+            [
+                'fr',
+                new Map([
+                    ['B', 'b'],
+                    ['A', 'a'],
+                ]),
+            ],
+            ['de', new Map()],
+            ['ar', new Map([['Z', 'z']])],
+        ])
+    );
+
+    assert.equal(
+        serialized,
+        '{\n    "ar": {\n        "Z": "z"\n    },\n    "fr": {\n        "A": "a",\n        "B": "b"\n    }\n}\n'
+    );
+});