@@ -0,0 +1,12 @@
+---
+'@objectstack/runtime': patch
+---
+
+fix(runtime): `GET /i18n/translations/:locale` carries an `ETag` and `Cache-Control: private, no-cache`, and a matching `If-None-Match` is answered `304`
+
+Clause-②: no
+Metadata-protocol: none
+
+- **Before.** The translation bundle (both spellings, `/i18n/translations/:locale` and `/i18n/translations?locale=`) answered every read with the whole locale bundle and neither header, so a browser re-downloaded it on every console open: 80–88 KB compressed on a hosted tenant.
+- **Now.** The `200` carries a weak `ETag`, a SHA-256 of the exact envelope served (`locale`, `requestedLocale` and `translations`), computed on every read, and `Cache-Control: private, no-cache`. A request whose `If-None-Match` names that representation (a strong or weak tag, a comma list, or `*`) is answered `304` with no body and the same two headers. A bundle that changed since the validator was issued is served in full under a new validator.
+- **Unchanged.** The `200` body is byte-for-byte the envelope it was. An anonymous caller is still refused `401` before any validator is read, and refusals carry neither header. `/i18n/locales` and `/i18n/labels/*` are untouched.
@@ -0,0 +1,83 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#25785] A dispatcher `304` reaches the caller as a body-less `304` with
+ * the route's own headers, through `toResponse`'s `response` arm.
+ *
+ * The `/i18n/translations` domain answers a matching `If-None-Match` with
+ * `{ status: 304, headers }` and no `body` (`runtime/src/domains/i18n.ts`,
+ * `translationsAnswer`). `toResponse` writes a `response` with `c.json(body,
+ * status)`; a `304` must reach the wire with NO body — a `Response` with a
+ * null-body status and a body throws in the Fetch constructor, and a body of
+ * `"null"` or `"undefined"` is not a `304` at all. This file pins that the
+ * body-less answer survives this adapter, and that the domain is handed the
+ * request headers it reads the validator from.
+ *
+ * The standalone server's half, over a real socket and the real domain, is
+ * `packages/runtime/src/i18n-translations-etag.hono.integration.test.ts`. This
+ * package's vitest config aliases `@objectstack/runtime` to a stub, so the
+ * dispatcher here is a fixture.
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import type { Hono } from 'hono';
+
+const mockDispatcher = {
+  getDiscoveryInfo: vi.fn().mockReturnValue({ version: '1.0', routes: {} }),
+  handleAuth: vi.fn(),
+  dispatch: vi.fn(),
+};
+
+vi.mock('@objectstack/runtime', () => ({
+  HttpDispatcher: function HttpDispatcher() { return mockDispatcher; },
+}));
+
+import { createHonoApp } from './index';
+
+const PREFIX = '/api/v1';
+const PATH = `${PREFIX}/i18n/translations/fr`;
+const ETAG = 'W/"validator-of-the-served-bundle"';
+const HEADERS = { ETag: ETAG, 'Cache-Control': 'private, no-cache' };
+
+const kernel = { name: 'test-kernel' } as any;
+const bootApp = (): Hono => createHonoApp({ kernel, prefix: PREFIX });
+
+describe('#25785: a body-less dispatcher 304 stays a body-less 304', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockDispatcher.handleAuth.mockResolvedValue({ handled: false });
+  });
+
+  it('is written as 304 with an empty body and the route\'s ETag and Cache-Control', async () => {
+    mockDispatcher.dispatch.mockResolvedValue({ handled: true, response: { status: 304, headers: HEADERS } });
+
+    const res = await bootApp().request(`http://localhost${PATH}`, { headers: { 'If-None-Match': ETAG } });
+
+    expect(res.status).toBe(304);
+    expect((await res.arrayBuffer()).byteLength).toBe(0);
+    expect(res.headers.get('etag')).toBe(ETAG);
+    expect(res.headers.get('cache-control')).toBe('private, no-cache');
+  });
+
+  it('hands the domain the request it reads If-None-Match from', async () => {
+    mockDispatcher.dispatch.mockResolvedValue({ handled: true, response: { status: 304, headers: HEADERS } });
+
+    await bootApp().request(`http://localhost${PATH}`, { headers: { 'If-None-Match': ETAG } });
+
+    expect(mockDispatcher.dispatch).toHaveBeenCalledTimes(1);
+    const context = mockDispatcher.dispatch.mock.calls[0][4];
+    expect(context.request.headers.get('if-none-match')).toBe(ETAG);
+  });
+
+  it('the 200 beside it still carries its JSON body and the same headers (control)', async () => {
+    const body = { success: true, data: { locale: 'fr', translations: { objects: {} } } };
+    mockDispatcher.dispatch.mockResolvedValue({ handled: true, response: { status: 200, body, headers: HEADERS } });
+
+    const res = await bootApp().request(`http://localhost${PATH}`);
+
+    expect(res.status).toBe(200);
+    await expect(res.json()).resolves.toEqual(body);
+    expect(res.headers.get('etag')).toBe(ETAG);
+    expect(res.headers.get('cache-control')).toBe('private, no-cache');
+  });
+});
@@ -0,0 +1,230 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #25785 — the translation bundle carries a validator, and a browser that
+ * holds the current bundle is answered `304` instead of the whole bundle.
+ *
+ * ## The defect
+ *
+ * `GET /i18n/translations/:locale` answered every console open with the whole
+ * locale bundle (288–361 KB raw, 80–88 KB compressed, measured on a hosted
+ * tenant) and no `ETag` or `Cache-Control`, so nothing let the browser
+ * revalidate what it already held.
+ *
+ * ## What is pinned
+ *
+ * - A: the `200` carries `ETag` and `Cache-Control: private, no-cache`, and its
+ *   body is the envelope it always was.
+ * - B: the validator is a hash of the bytes served — read here by recomputing
+ *   it from the body, so a validator derived from anything cheaper (a counter,
+ *   the bundle's identity) fails this file, not production.
+ * - C: `If-None-Match` naming that representation, in every spelling RFC 9110
+ *   §13.1.2 allows (strong or weak, a list, `*`) and through both header shapes
+ *   a transport hands in, is answered `304` with the same two headers and no
+ *   body; a stale or malformed one is served the full bundle.
+ * - D: the anonymous floor still decides first — a matching validator does not
+ *   turn the `401` into a `304`, and no refusal carries a validator.
+ *
+ * The wire half (both headers and the empty `304` over a real socket) is
+ * `i18n-translations-etag.hono.integration.test.ts`.
+ */
+
+import { createHash } from 'node:crypto';
+import { describe, it, expect, vi } from 'vitest';
+
+import { handleI18nRequest } from './i18n.js';
+import { apiErrorResponse } from '../error-envelope.js';
+import type { DomainHandlerDeps } from '../domain-handler-registry.js';
+import type { HttpProtocolContext } from '../http-dispatcher.js';
+
+const MEMBER_EC = { userId: 'usr_member', isSystem: false, positions: [], permissions: [], systemPermissions: [] };
+
+function member(headers: unknown = {}): HttpProtocolContext {
+    return { request: { headers }, executionContext: { ...MEMBER_EC } } as unknown as HttpProtocolContext;
+}
+
+function anonymous(headers: unknown = {}): HttpProtocolContext {
+    return { request: { headers } } as unknown as HttpProtocolContext;
+}
+
+function makeService(bundles: Record<string, Record<string, unknown>>) {
+    return {
+        getLocales: vi.fn(() => Object.keys(bundles)),
+        getDefaultLocale: vi.fn(() => 'en'),
+        getTranslations: vi.fn((locale: string) => bundles[locale] ?? {}),
+    };
+}
+
+function makeDeps(service: ReturnType<typeof makeService>): DomainHandlerDeps {
+    return {
+        getService: vi.fn(async () => service),
+        resolveService: vi.fn(async () => service),
+        // The dispatcher's own envelope builder, `meta` slot included.
+        success: (data: any, meta?: any) => ({ status: 200, body: { success: true, data, meta } }),
+        error: (message: string, httpStatus = 500, details?: any) =>
+            apiErrorResponse({ message, httpStatus, details }),
+    } as unknown as DomainHandlerDeps;
+}
+
+const FR = { objects: { lead: { label: 'Prospect', fields: { company: { label: 'Société' } } } } };
+const ZH_CN = { objects: { lead: { label: '潜在客户' } } };
+
+/** The validator of a served body, recomputed from the bytes the transport writes. */
+function validatorOf(body: unknown): string {
+    return `W/"${createHash('sha256').update(JSON.stringify(body)).digest('base64url')}"`;
+}
+
+async function read(
+    service: ReturnType<typeof makeService>,
+    context: HttpProtocolContext,
+    input: { subPath: string; query?: Record<string, unknown> } = { subPath: '/translations/fr' },
+): Promise<any> {
+    return handleI18nRequest(makeDeps(service), input.subPath, 'GET', input.query ?? {}, context);
+}
+
+// ── A + B: the 200 and its validator ────────────────────────────────────────
+
+describe('#25785 A — a translations read carries its validator and cache directive', () => {
+    it.each([
+        ['the path spelling', { subPath: '/translations/fr' }],
+        ['the query spelling', { subPath: '/translations', query: { locale: 'fr' } }],
+    ])('%s: 200, the same body as before, plus ETag and Cache-Control: private, no-cache', async (_label, input) => {
+        const result = await read(makeService({ en: {}, fr: FR }), member(), input);
+        expect(result.handled).toBe(true);
+        expect(result.response.status).toBe(200);
+        expect(result.response.body).toEqual({ success: true, data: { locale: 'fr', translations: FR } });
+        expect(result.response.headers['Cache-Control']).toBe('private, no-cache');
+        expect(result.response.headers.ETag).toMatch(/^W\/"[A-Za-z0-9_-]{43}"$/);
+    });
+
+    it('the locale fallback arm (zh → zh-CN) carries them too, over its own body', async () => {
+        const result = await read(makeService({ en: {}, 'zh-CN': ZH_CN }), member(), { subPath: '/translations/zh' });
+        expect(result.response.status).toBe(200);
+        expect(result.response.body.data).toEqual({ locale: 'zh-CN', requestedLocale: 'zh', translations: ZH_CN });
+        expect(result.response.headers['Cache-Control']).toBe('private, no-cache');
+        expect(result.response.headers.ETag).toBe(validatorOf(result.response.body));
+    });
+
+    it('a refusal carries no validator: the missing-locale 400', async () => {
+        const result = await read(makeService({ fr: FR }), member(), { subPath: '/translations', query: {} });
+        expect(result.response.status).toBe(400);
+        expect(result.response.headers).toBeUndefined();
+    });
+});
+
+describe('#25785 B — the validator is a hash of the bytes served, recomputed on every read', () => {
+    it('equals the hash of the served envelope', async () => {
+        const result = await read(makeService({ fr: FR }), member());
+        expect(result.response.headers.ETag).toBe(validatorOf(result.response.body));
+    });
+
+    it('is stable while the bundle is unchanged, and moves when one string changes', async () => {
+        const bundles: Record<string, Record<string, unknown>> = { fr: FR };
+        const service = makeService(bundles);
+        const first = (await read(service, member())).response.headers.ETag;
+        expect((await read(service, member())).response.headers.ETag).toBe(first);
+
+        bundles.fr = { objects: { lead: { label: 'Prospect', fields: { company: { label: 'Entreprise' } } } } };
+        const changed = await read(service, member());
+        expect(changed.response.headers.ETag).not.toBe(first);
+        expect(changed.response.headers.ETag).toBe(validatorOf(changed.response.body));
+    });
+
+    it('moves when the bundle object is MUTATED in place — identity is not the validator', async () => {
+        const mutable = { objects: { lead: { label: 'Prospect' } } } as Record<string, any>;
+        const service = makeService({ fr: mutable });
+        const before = (await read(service, member())).response.headers.ETag;
+        mutable.objects.lead.label = 'Piste';
+        expect((await read(service, member())).response.headers.ETag).not.toBe(before);
+    });
+});
+
+// ── C: the conditional read ─────────────────────────────────────────────────
+
+describe('#25785 C — If-None-Match naming the current bundle is answered 304, with no body', () => {
+    async function currentValidator(): Promise<string> {
+        return (await read(makeService({ fr: FR }), member())).response.headers.ETag;
+    }
+
+    function expectNotModified(result: any, etag: string) {
+        expect(result.handled).toBe(true);
+        expect(result.response.status).toBe(304);
+        expect('body' in result.response).toBe(false);
+        // RFC 9110 §15.4.5: the 304 carries the ETag and Cache-Control the 200 would.
+        expect(result.response.headers).toEqual({ ETag: etag, 'Cache-Control': 'private, no-cache' });
+    }
+
+    it.each([
+        ['the weak tag it was served', (etag: string) => etag],
+        ['the strong spelling of it (weak comparison)', (etag: string) => etag.replace(/^W\//, '')],
+        ['a list naming it after another tag', (etag: string) => `W/"stale", ${etag}`],
+        ['a list without spaces', (etag: string) => `"stale",${etag}`],
+        ['*', () => '*'],
+    ])('%s → 304', async (_label, spell) => {
+        const etag = await currentValidator();
+        expectNotModified(await read(makeService({ fr: FR }), member({ 'if-none-match': spell(etag) })), etag);
+    });
+
+    it('through a Fetch Headers object (the @objectstack/hono catch-all hands its raw Request)', async () => {
+        const etag = await currentValidator();
+        expectNotModified(await read(makeService({ fr: FR }), member(new Headers({ 'If-None-Match': etag }))), etag);
+    });
+
+    it('through a repeated header in the record shape, read as one list', async () => {
+        const etag = await currentValidator();
+        expectNotModified(await read(makeService({ fr: FR }), member({ 'if-none-match': ['W/"stale"', etag] })), etag);
+    });
+
+    it('on the query spelling too', async () => {
+        const etag = await currentValidator();
+        const result = await read(
+            makeService({ fr: FR }), member({ 'if-none-match': etag }), { subPath: '/translations', query: { locale: 'fr' } },
+        );
+        expectNotModified(result, etag);
+    });
+
+    it.each([
+        ['a stale validator', 'W/"stale"'],
+        ['an unquoted value (malformed: matches nothing)', 'stale'],
+        ['an empty header', ''],
+    ])('%s is served the full bundle with the current validator', async (_label, header) => {
+        const etag = await currentValidator();
+        const result = await read(makeService({ fr: FR }), member({ 'if-none-match': header }));
+        expect(result.response.status).toBe(200);
+        expect(result.response.body).toEqual({ success: true, data: { locale: 'fr', translations: FR } });
+        expect(result.response.headers.ETag).toBe(etag);
+    });
+
+    it('a validator issued before the bundle changed is served the new bundle, never a 304', async () => {
+        const bundles: Record<string, Record<string, unknown>> = { fr: FR };
+        const service = makeService(bundles);
+        const issued = (await read(service, member())).response.headers.ETag;
+        bundles.fr = { objects: { lead: { label: 'Piste' } } };
+        const result = await read(service, member({ 'if-none-match': issued }));
+        expect(result.response.status).toBe(200);
+        expect(result.response.body.data.translations).toEqual({ objects: { lead: { label: 'Piste' } } });
+        expect(result.response.headers.ETag).not.toBe(issued);
+    });
+
+    it('a validator for one locale does not answer another locale 304', async () => {
+        const service = makeService({ fr: FR, 'zh-CN': ZH_CN });
+        const frEtag = (await read(service, member())).response.headers.ETag;
+        const result = await read(service, member({ 'if-none-match': frEtag }), { subPath: '/translations/zh-CN' });
+        expect(result.response.status).toBe(200);
+        expect(result.response.body.data.translations).toEqual(ZH_CN);
+    });
+});
+
+// ── D: the floor decides first ──────────────────────────────────────────────
+
+describe('#25785 D — the anonymous floor still answers before any validator is read', () => {
+    it('an anonymous caller holding the current validator gets 401, no 304 and no headers', async () => {
+        const etag = (await read(makeService({ fr: FR }), member())).response.headers.ETag;
+        const service = makeService({ fr: FR });
+        const result = await read(service, anonymous({ 'if-none-match': etag }));
+        expect(result.response.status).toBe(401);
+        expect(result.response.body.error.code).toBe('UNAUTHENTICATED');
+        expect(result.response.headers).toBeUndefined();
+        expect(service.getTranslations).not.toHaveBeenCalled();
+    });
+});