@@ -0,0 +1,11 @@
+---
+"@objectstack/hono": patch
+---
+
+fix(hono): on a `createHonoApp` host, `GET /api/v1/mcp/skill` answers the raw markdown with one `Content-Type: text/markdown; charset=utf-8` and `Cache-Control: no-store`, as the standalone server does
+
+Clause-②: no
+
+- **What a caller got.** The skill is served as a single string event on the dispatcher's `result` stream channel. The adapter's stream writer framed every event outside a Vercel data stream as `data: <JSON>`, so the body was an SSE frame of a JSON-encoded string (`data: "---\nname: …"`), not markdown. It also set its own `Content-Type` and `Cache-Control` beside the domain's, so the answer carried `text/markdown; charset=utf-8, text/markdown; charset=utf-8` and `no-cache, no-store` (on a socket: two `Content-Type` lines and two `Cache-Control` lines).
+- **What it answers now.** A string event is written as given, in every stream mode, and a header the producer sets replaces the adapter's default of the same name, whatever its case. Object events are still one `data:` frame each (one JSON line in a Vercel data stream), and a stream that sets no headers still gets `text/event-stream`, `no-cache` and `keep-alive`.
+- **Unchanged:** the AI chat streams, which reach the same writer as pre-encoded Vercel data stream frames or as object parts, and every other route.
@@ -0,0 +1,111 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#24287] `toResponse`'s events arm writes a string event as given, and a
+ * producer's own header replaces the default it names.
+ *
+ * The standalone server's writer (`runtime/src/dispatcher-plugin.ts`,
+ * `sendResultBase`) writes a string event verbatim and an object event as one
+ * SSE frame, and a route's header replaces the default. This arm SSE-framed
+ * every event outside a Vercel data stream and appended the producer's
+ * lowercase headers beside its own capitalised defaults, so the `/mcp/skill`
+ * domain's single markdown chunk reached the caller as `data: "# skill"` under
+ * a doubled `Content-Type` and `no-cache, no-store`.
+ *
+ * The rows below are the producers that reach this arm: the `/mcp/skill`
+ * domain (`runtime/src/domains/mcp.ts`), and the `/ai` domain
+ * (`runtime/src/domains/ai.ts`) in both its shapes — a Vercel data stream of
+ * pre-encoded string frames, and an SSE stream of object parts. The two `/ai`
+ * rows pin answers this card leaves unchanged. The dispatcher is a fixture
+ * (this package's config aliases `@objectstack/runtime` to a stub); the same
+ * skill row through the real dispatcher and both doors is
+ * `packages/qa/http-conformance/src/hono-mcp-skill-raw-body.conformance.test.ts`.
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+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 kernel = { name: 'test-kernel' } as any;
+
+async function* events(...items: unknown[]) {
+  for (const item of items) yield item;
+}
+
+async function get(result: Record<string, unknown>): Promise<Response> {
+  mockDispatcher.dispatch.mockResolvedValue({ handled: true, result: { type: 'stream', ...result } });
+  const app = createHonoApp({ kernel, prefix: PREFIX, cors: false });
+  return app.request(`http://hosted.test${PREFIX}/some/stream`);
+}
+
+beforeEach(() => {
+  mockDispatcher.dispatch.mockReset();
+});
+
+describe('[#24287] toResponse events arm: string events verbatim, producer headers replace defaults', () => {
+  it('the /mcp/skill shape: the markdown verbatim, and each declared header once', async () => {
+    const markdown = '---\nname: objectstack\n---\n\n# skill "quoted"\n';
+    const res = await get({
+      status: 200,
+      contentType: 'text/markdown; charset=utf-8',
+      headers: {
+        'content-type': 'text/markdown; charset=utf-8',
+        'content-disposition': 'inline; filename="SKILL.md"',
+        'cache-control': 'no-store',
+      },
+      events: events(markdown),
+    });
+
+    expect(res.status).toBe(200);
+    expect(await res.text()).toBe(markdown);
+    expect(res.headers.get('content-type')).toBe('text/markdown; charset=utf-8');
+    expect(res.headers.get('cache-control')).toBe('no-store');
+    expect(res.headers.get('content-disposition')).toBe('inline; filename="SKILL.md"');
+  });
+
+  it('an object event outside a Vercel data stream is still one SSE frame, under the SSE defaults', async () => {
+    const res = await get({ contentType: 'text/event-stream', events: events({ type: 'text-delta', text: 'hi' }, { type: 'finish' }) });
+
+    expect(await res.text()).toBe('data: {"type":"text-delta","text":"hi"}\n\ndata: {"type":"finish"}\n\n');
+    expect(res.headers.get('content-type')).toBe('text/event-stream');
+    expect(res.headers.get('cache-control')).toBe('no-cache');
+    expect(res.headers.get('connection')).toBe('keep-alive');
+  });
+
+  it('the /ai SSE shape (object parts, capitalised headers): unchanged', async () => {
+    const res = await get({
+      contentType: 'text/event-stream',
+      events: events({ type: 'text-delta', id: '0', text: 'a' }),
+      headers: { 'Content-Type': 'text/event-stream', 'Cache-Control': 'no-cache', 'Connection': 'keep-alive' },
+    });
+
+    expect(await res.text()).toBe('data: {"type":"text-delta","id":"0","text":"a"}\n\n');
+    expect(res.headers.get('content-type')).toBe('text/event-stream');
+    expect(res.headers.get('cache-control')).toBe('no-cache');
+  });
+
+  it('the /ai Vercel data stream shape (pre-encoded string frames): unchanged', async () => {
+    const frames = ['data: {"type":"start"}\n\n', 'data: {"type":"text-delta","id":"0","delta":"a"}\n\n', 'data: [DONE]\n\n'];
+    const res = await get({
+      contentType: 'text/plain; charset=utf-8',
+      vercelDataStream: true,
+      events: events(...frames, { type: 'raw' }),
+      headers: { 'Content-Type': 'text/plain; charset=utf-8', 'Cache-Control': 'no-cache', 'Connection': 'keep-alive' },
+    });
+
+    expect(await res.text()).toBe(`${frames.join('')}{"type":"raw"}\n`);
+    expect(res.headers.get('content-type')).toBe('text/plain; charset=utf-8');
+    expect(res.headers.get('cache-control')).toBe('no-cache');
+  });
+});
@@ -820,21 +820,40 @@ export function createHonoApp(options: ObjectStackHonoOptions): Hono {
           return c.redirect(res.url);
         }
         if (res.type === 'stream' && res.events) {
-          // SSE / Vercel Data Stream streaming response
-          const headers: Record<string, string> = {
+          /**
+           * [#24287] SSE / Vercel Data Stream / raw single-chunk response.
+           *
+           * A string event is written as given, in every mode; an object
+           * event is one SSE frame (or one JSON line in a Vercel data
+           * stream). A producer's own header replaces the default it names,
+           * matched case-insensitively. That is what the standalone server's
+           * writer does (`runtime/src/dispatcher-plugin.ts`,
+           * `sendResultBase`), and what `/mcp/skill`'s domain relies on: it
+           * serves the markdown as one string event under its own lowercase
+           * `content-type` and `cache-control`. This arm used to SSE-frame
+           * every event outside a Vercel data stream and spread those headers
+           * into a record beside its capitalised defaults, so the caller got
+           * `data: "# skill"` under a doubled `Content-Type` and
+           * `no-cache, no-store`. The `/ai` domain's two shapes reach this arm
+           * too — pre-encoded string frames with `vercelDataStream`, object
+           * parts without it — and both answer as before.
+           */
+          const headers = new Headers({
             'Content-Type': res.contentType || 'text/event-stream',
             'Cache-Control': 'no-cache',
             'Connection': 'keep-alive',
-            ...(res.headers || {}),
-          };
+          });
+          for (const [k, v] of Object.entries(res.headers || {})) headers.set(k, String(v));
           const stream = new ReadableStream({
             async start(controller) {
               try {
                 const encoder = new TextEncoder();
                 for await (const event of res.events) {
-                  const chunk = res.vercelDataStream
-                    ? (typeof event === 'string' ? event : JSON.stringify(event) + '\n')
-                    : `data: ${JSON.stringify(event)}\n\n`;
+                  const chunk = typeof event === 'string'
+                    ? event
+                    : res.vercelDataStream
+                      ? JSON.stringify(event) + '\n'
+                      : `data: ${JSON.stringify(event)}\n\n`;
                   controller.enqueue(encoder.encode(chunk));
                 }
               } catch (err) {
 
@@ -0,0 +1,118 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#24287] On a `createHonoApp` host, `GET /api/v1/mcp/skill` answers the raw
+ * markdown the standalone server answers — through the host's own pipeline.
+ *
+ * ## The defect
+ *
+ * `handleMcpSkillRequest` (`packages/runtime/src/domains/mcp.ts`) serves the
+ * skill as a single-chunk `result` stream: one string event, its own lowercase
+ * `content-type` / `content-disposition` / `cache-control`. The standalone
+ * server writes a string event verbatim and lets the domain's headers replace
+ * its defaults. `toResponse`'s events arm in `@objectstack/hono` SSE-framed
+ * every event outside a Vercel data stream (`data: ${JSON.stringify(event)}`)
+ * and appended the domain's headers beside its own capitalised defaults.
+ * Measured through this host before the fix:
+ *
+ *     GET /api/v1/mcp/skill
+ *       body          : data: "---\nname: objectstack\n---\n\n# …"   (an SSE frame of a JSON string)
+ *       content-type  : text/markdown; charset=utf-8, text/markdown; charset=utf-8
+ *       cache-control : no-cache, no-store
+ *
+ * ## What is pinned
+ *
+ *  1. On the hosted door (`app.request` into the Hono app `createHonoApp`
+ *     returns): the body is the markdown byte for byte, and the three headers
+ *     the domain declares are each its one value.
+ *  2. The hosted answer equals the standalone answer (`HonoServerPlugin` + the
+ *     dispatcher plugin, over a real socket): status, body and those headers.
+ *
+ * The skill text carries newlines, double quotes and a non-ASCII character, so
+ * any JSON or SSE encoding of it differs from it. A real socket on a
+ * `createHonoApp` host is not booted here. `LiteKernel`, a fake `mcp` service
+ * that renders only the skill.
+ */
+
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { LiteKernel } from '@objectstack/core';
+import type { Plugin, PluginContext } from '@objectstack/core';
+import { HonoServerPlugin } from '@objectstack/plugin-hono-server';
+import { createDispatcherPlugin } from '@objectstack/runtime';
+import { createHonoApp } from '@objectstack/hono';
+import type { IHttpServer } from '@objectstack/spec/contracts';
+
+const PREFIX = '/api/v1';
+const SKILL = '---\nname: objectstack\ndescription: "Use the MCP server"\n---\n\n# Skill — fixture\n\nLine two.\n';
+
+/** The headers the skill domain declares, each with its one value. */
+const SKILL_HEADERS: Record<string, string> = {
+    'content-type': 'text/markdown; charset=utf-8',
+    'content-disposition': 'inline; filename="SKILL.md"',
+    'cache-control': 'no-store',
+};
+
+function fakeMcpPlugin(): Plugin {
+    return {
+        name: 'com.objectstack.test.fake-mcp-skill-raw-body',
+        version: '1.0.0',
+        init: async (ctx: PluginContext) => {
+            ctx.registerService('mcp', { renderSkill: () => SKILL });
+        },
+    };
+}
+
+describe('[#24287] GET /mcp/skill answers the raw markdown on a createHonoApp host (conformance)', () => {
+    let hostedKernel: LiteKernel;
+    let standaloneKernel: LiteKernel;
+    let hosted: () => Promise<Response>;
+    let standalone: () => Promise<Response>;
+
+    beforeAll(async () => {
+        hostedKernel = new LiteKernel();
+        hostedKernel.use(fakeMcpPlugin());
+        await hostedKernel.bootstrap();
+        const app = createHonoApp({ kernel: hostedKernel as any, prefix: PREFIX, cors: false });
+        hosted = async () => app.request(`http://hosted.test${PREFIX}/mcp/skill`);
+
+        standaloneKernel = new LiteKernel();
+        standaloneKernel.use(fakeMcpPlugin());
+        standaloneKernel.use(new HonoServerPlugin({ port: 0, cors: false }));
+        standaloneKernel.use(createDispatcherPlugin({ prefix: PREFIX, securityHeaders: false }));
+        await standaloneKernel.bootstrap();
+        const base = `http://127.0.0.1:${standaloneKernel.getService<IHttpServer>('http.server').getPort!()}`;
+        standalone = () => fetch(`${base}${PREFIX}/mcp/skill`);
+    }, 30_000);
+
+    afterAll(async () => {
+        for (const kernel of [hostedKernel, standaloneKernel]) {
+            if (!kernel) continue;
+            await Promise.race([kernel.shutdown(), new Promise<void>((resolve) => setTimeout(resolve, 10_000))]);
+        }
+    }, 30_000);
+
+    it('the hosted door answers the markdown verbatim, with one value per declared header', async () => {
+        const res = await hosted();
+
+        expect(res.status).toBe(200);
+        expect(await res.text()).toBe(SKILL);
+        // `Headers.get` joins repeated values with ", ", so equality is one value.
+        for (const [name, value] of Object.entries(SKILL_HEADERS)) {
+            expect(res.headers.get(name), name).toBe(value);
+        }
+    });
+
+    it('the hosted answer is the standalone answer', async () => {
+        const viaHost = await hosted();
+        const viaStandalone = await standalone();
+
+        expect(viaStandalone.status).toBe(200);
+        expect(viaHost.status).toBe(viaStandalone.status);
+        const standaloneBody = await viaStandalone.text();
+        expect(standaloneBody).toBe(SKILL);
+        expect(await viaHost.text()).toBe(standaloneBody);
+        for (const name of Object.keys(SKILL_HEADERS)) {
+            expect(viaHost.headers.get(name), name).toBe(viaStandalone.headers.get(name));
+        }
+    });
+});