fix(runtime-ts): ensure byte-identical /_meta headers across fastify and hono

Extract shared content-type constant and tighten test assertions to verify
both frameworks serve identical headers. The Hono test now asserts the
content-type header (previously missing), Fastify test uses exact equality
instead of substring match, and both mounts import from a single constant
to prevent header drift.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015NrWUxA6euwvnFcwKxcK6A

Author: dmealing

server/typescript/packages/runtime-ts/src/fastify/index.ts

@@ -262,7 +262,7 @@ export { parseId } from "../drizzle-fastify/util.js";
 // ---------------------------------------------------------------------------
 
 import type { MetaData } from "@metaobjectsdev/metadata";
-import { META_ROUTE_PATH, metaJson } from "../meta-endpoint.js";
+import { META_ROUTE_PATH, META_CONTENT_TYPE, metaJson } from "../meta-endpoint.js";
 
 export interface MetaRouteOptions {
   fastify: FastifyInstance;
@@ -292,7 +292,7 @@ export function mountMetaRoute(opts: MetaRouteOptions): void {
   opts.fastify.get(path, async (_req, reply) => {
     return reply
       .code(200)
-      .header("content-type", "application/json; charset=utf-8")
+      .header("content-type", META_CONTENT_TYPE)
       .send(metaJson(opts.root));
   });
 }

server/typescript/packages/runtime-ts/src/hono/index.ts

@@ -326,7 +326,7 @@ export { mountReadOnlyCrudRoutes, type MountReadOnlyOptions } from "./mount-read
 // ---------------------------------------------------------------------------
 
 import type { MetaData } from "@metaobjectsdev/metadata";
-import { META_ROUTE_PATH, metaJson } from "../meta-endpoint.js";
+import { META_ROUTE_PATH, META_CONTENT_TYPE, metaJson } from "../meta-endpoint.js";
 
 export interface HonoMetaRouteOptions {
   app: AnyHono;
@@ -344,6 +344,6 @@ export interface HonoMetaRouteOptions {
 export function mountMetaRouteHono(opts: HonoMetaRouteOptions): void {
   const path = `${opts.prefix ?? ""}${META_ROUTE_PATH}`;
   opts.app.get(path, (c) =>
-    c.body(metaJson(opts.root), 200, { "content-type": "application/json; charset=utf-8" }),
+    c.body(metaJson(opts.root), 200, { "content-type": META_CONTENT_TYPE }),
   );
 }

server/typescript/packages/runtime-ts/src/index.ts

@@ -50,4 +50,4 @@ export {
 } from "./constraint-errors.js";
 
 // UI-1 — metadata API contract for the browser read-model.
-export { META_ROUTE_PATH, metaJson } from "./meta-endpoint.js";
+export { META_ROUTE_PATH, META_CONTENT_TYPE, metaJson } from "./meta-endpoint.js";

server/typescript/packages/runtime-ts/src/meta-endpoint.ts

@@ -10,6 +10,14 @@ import { canonicalSerializeEffective, type MetaData } from "@metaobjectsdev/meta
  */
 export const META_ROUTE_PATH = "/_meta";
 
+/**
+ * The `GET {apiPrefix}/_meta` response content-type header.
+ * A cross-port contract value — one browser read-model has to work against
+ * every backend, so the header must be byte-identical across all Fastify and
+ * Hono mounts.
+ */
+export const META_CONTENT_TYPE = "application/json; charset=utf-8";
+
 /**
  * The `GET {apiPrefix}/_meta` response body: the loaded model as EFFECTIVE
  * canonical JSON.

server/typescript/packages/runtime-ts/test/meta-route.test.ts

@@ -1,7 +1,7 @@
 import { describe, test, expect } from "bun:test";
 import Fastify from "fastify";
 import { Hono } from "hono";
-import { metaJson } from "../src/meta-endpoint.js";
+import { metaJson, META_CONTENT_TYPE } from "../src/meta-endpoint.js";
 import { mountMetaRoute } from "../src/fastify/index.js";
 import { mountMetaRouteHono } from "../src/hono/index.js";
 import { loadTestModel } from "./helpers/load-test-model.js";
@@ -16,7 +16,7 @@ describe("GET /_meta (fastify)", () => {
     const res = await app.inject({ method: "GET", url: "/api/_meta" });
 
     expect(res.statusCode).toBe(200);
-    expect(res.headers["content-type"]).toContain("application/json");
+    expect(res.headers["content-type"]).toBe(META_CONTENT_TYPE);
     expect(res.body).toBe(metaJson(root));
   });
 
@@ -31,14 +31,15 @@ describe("GET /_meta (fastify)", () => {
 });
 
 describe("GET /_meta (hono)", () => {
-  test("serves the same bytes as the fastify mount", async () => {
+  test("serves the same bytes and headers as the fastify mount", async () => {
     const root = await loadTestModel();
     const app = new Hono();
     mountMetaRouteHono({ app, root, prefix: "/api" });
 
     const res = await app.request("/api/_meta");
 
     expect(res.status).toBe(200);
+    expect(res.headers.get("content-type")).toBe(META_CONTENT_TYPE);
     expect(await res.text()).toBe(metaJson(root));
   });
 });