fix(mcp): stream editor bridges through reverse proxies

server/ai/mcp/editorBridge.ts

@@ -4,10 +4,11 @@
  * Browser-execution tools (insert HTML, apply CSS, set tokens, manage pages,
  * content CRUD, …) have no server implementation — their logic runs in the
  * editor app against the live store. To let an external MCP client use them,
- * the editor holds a long-lived NDJSON stream open while mounted; this module
- * keeps one bridge per user and workspace (the newest open instance wins)
- * and lets the MCP server relay a browser tool call to the correct workspace
- * before awaiting its result.
+ * the editor holds a long-lived newline-delimited JSON stream open while
+ * mounted. Its HTTP response is advertised as an event stream so reverse
+ * proxies preserve incremental delivery. This module keeps one bridge per user
+ * and workspace (the newest open instance wins) and lets the MCP server relay a
+ * browser tool call to the correct workspace before awaiting its result.
  *
  * Reuses the chat bridge machinery wholesale: `createBridge` issues the
  * `AiBrowserBridge` (whose `callBrowser` resolves when the editor POSTs back to

server/ai/mcp/handlers/editorBridge.ts

@@ -1,11 +1,13 @@
 /**
  * Workspace bridge stream — `GET /admin/api/ai/editor-bridge?scope=…`.
  *
- * The Site editor and Content workspace each open their own NDJSON stream so
- * MCP browser tools are relayed to the workspace that owns the tool (see
- * `../editorBridge.ts`). Authenticated by the admin session; each bridge is
- * registered under the session user + scope, so it can only serve that user's
- * own MCP connectors. Results flow back through the existing
+ * The Site editor and Content workspace each open their own newline-delimited
+ * JSON stream so MCP browser tools are relayed to the workspace that owns the
+ * tool (see `../editorBridge.ts`). The response uses the event-stream media type
+ * so reverse proxies flush each record instead of buffering this long-lived
+ * connection. Authenticated by the admin session; each bridge is registered
+ * under the session user + scope, so it can only serve that user's own MCP
+ * connectors. Results flow back through the existing
  * `POST /admin/api/ai/tool-result` endpoint.
  */
 import { Type, safeParseValue } from '@core/utils/typeboxHelpers'
@@ -81,8 +83,11 @@ async function handle(req: Request, db: DbClient): Promise<Response> {
   return new Response(stream, {
     status: 200,
     headers: {
-      'Content-Type': 'application/x-ndjson',
-      'Cache-Control': 'no-cache',
+      // Kamal Proxy flushes event streams incrementally, while generic NDJSON
+      // responses may be buffered until this long-lived bridge closes. The
+      // browser deliberately parses the payload as newline-delimited JSON.
+      'Content-Type': 'text/event-stream',
+      'Cache-Control': 'no-cache, no-transform',
       'X-Accel-Buffering': 'no',
     },
   })

src/__tests__/agent/contentBridge.test.ts

@@ -190,6 +190,7 @@ describe('runMcpWorkspaceBridgeConnection', () => {
     globalThis.fetch = (async (_input, init) => {
       requestCount += 1
       if (requestCount === 1) {
+        expect(init?.headers).toEqual({ Accept: 'text/event-stream' })
         const signal = init?.signal as AbortSignal
         expect(signal.aborted).toBe(false)
         connectionSignals.push(signal)
@@ -212,6 +213,7 @@ describe('runMcpWorkspaceBridgeConnection', () => {
       }
 
       const signal = init?.signal as AbortSignal
+      expect(init?.headers).toEqual({ Accept: 'text/event-stream' })
       expect(signal.aborted).toBe(false)
       connectionSignals.push(signal)
       return new Response(null, { status: 401 })

src/__tests__/ai/mcpEditorBridgeHandler.test.ts

@@ -58,7 +58,9 @@ describe('MCP editor bridge handler', () => {
       signal: siteCtrl.signal,
     })
     expect(siteAllowed.status).toBe(200)
-    expect(siteAllowed.headers.get('content-type')).toBe('application/x-ndjson')
+    expect(siteAllowed.headers.get('content-type')).toBe('text/event-stream')
+    expect(siteAllowed.headers.get('cache-control')).toBe('no-cache, no-transform')
+    expect(siteAllowed.headers.get('x-accel-buffering')).toBe('no')
     siteCtrl.abort()
 
     const contentCtrl = new AbortController()
@@ -67,7 +69,9 @@ describe('MCP editor bridge handler', () => {
       signal: contentCtrl.signal,
     })
     expect(contentAllowed.status).toBe(200)
-    expect(contentAllowed.headers.get('content-type')).toBe('application/x-ndjson')
+    expect(contentAllowed.headers.get('content-type')).toBe('text/event-stream')
+    expect(contentAllowed.headers.get('cache-control')).toBe('no-cache, no-transform')
+    expect(contentAllowed.headers.get('x-accel-buffering')).toBe('no')
     contentCtrl.abort()
   })
 })

src/admin/ai/useMcpWorkspaceBridge.ts

@@ -78,7 +78,9 @@ export async function runMcpWorkspaceBridgeConnection(
     const res = await fetch(`${MCP_BRIDGE_PATH}?scope=${scope}`, {
       method: 'GET',
       credentials: 'same-origin',
-      headers: { Accept: 'application/x-ndjson' },
+      // The bridge body stays newline-delimited JSON, but the event-stream
+      // media type prevents reverse proxies from buffering the open response.
+      headers: { Accept: 'text/event-stream' },
       signal,
     })
     if (res.status === 401 || res.status === 403) return 'auth'