test(mcplocal): prove chat SSE streams live through the proxy, not buffered

`mcpctl chat reviewer` showed nothing until the turn finished, then dumped
the whole answer at once. mcpd streams token deltas and the CLI renders
them incrementally — the sole buffering point was mcplocal's catch-all
/api/v1/* proxy reading the whole SSE body via res.text() before replying.
The previous commit (cherry-picked from feat/agentic-teams) pipes the body
through instead; this one adds the cover that was missing:

- proxy-long-running.test.ts: a progressive-delivery test in which the
  stand-in mcpd withholds its final frame until the client has observed the
  first delta through the proxy. A buffering proxy cannot satisfy that
  ordering — verified: the test fails in 3s (no hang) against a res.text()
  proxy and passes against the piped one. The existing SSE test used
  inject(), which collects the whole body and so passes either way.

- agent-chat.smoke.test.ts: a live smoke that posts through mcplocal on
  localhost:3200 (the path `mcpctl chat` actually takes — every other chat
  smoke uses --direct and bypasses the proxy entirely) and asserts delta
  frames arrive spread across the generation window, not in one burst at
  stream end. Uses its own agent: the shared smoke agent pins replies to a
  single token, too short to tell live streaming from a buffer dump.

Also settles the strict-boolean-expressions lint on the auth-header check
the streaming split touched.

Local: workspace 2546 passed, proxy suite 10/10, smoke file loads + self-skips.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dNpnBqyyz9GxfznVcX2sP

src/mcplocal/src/http/index.ts

@@ -2,7 +2,7 @@ export { createHttpServer } from './server.js';
 export type { HttpServerDeps } from './server.js';
 export { loadHttpConfig } from './config.js';
 export type { HttpConfig } from './config.js';
-export { McpdClient, AuthenticationError, ConnectionError } from './mcpd-client.js';
+export { McpdClient, AuthenticationError, ConnectionError, UpstreamTimeoutError } from './mcpd-client.js';
 export { registerProxyRoutes } from './routes/proxy.js';
 export { registerMcpEndpoint } from './mcp-endpoint.js';
 export { registerProjectMcpEndpoint } from './project-mcp-endpoint.js';

src/mcplocal/src/http/mcpd-client.ts

@@ -20,9 +20,41 @@ export class ConnectionError extends Error {
   }
 }
 
+/**
+ * Thrown when mcpd was reachable but did not finish in time.
+ *
+ * Deliberately NOT a ConnectionError. Folding timeouts into "cannot connect"
+ * is what made this class of failure so expensive to diagnose: mcpd answered
+ * /healthz in 32ms while the proxy insisted the daemon was down. A timeout and
+ * an unreachable daemon need different messages and different status codes.
+ */
+export class UpstreamTimeoutError extends Error {
+  constructor(readonly url: string, readonly timeoutMs: number) {
+    super(`mcpd did not respond within ${String(timeoutMs)}ms: ${url}`);
+    this.name = 'UpstreamTimeoutError';
+  }
+}
+
+/** True when `err` is an AbortSignal.timeout() firing. */
+function isTimeout(err: unknown): boolean {
+  return err instanceof DOMException && err.name === 'TimeoutError';
+}
+
 /** Default timeout for mcpd requests (ms). Prevents indefinite hangs on slow upstream tool calls. */
 export const DEFAULT_TIMEOUT_MS = 30_000;
 
+/**
+ * Budget for routes that are *expected* to run long: agent/project chat and
+ * raw inference. An agent turn is a multi-turn tool-use loop and legitimately
+ * runs for minutes, so the 30s default is not a safety net there — it is a
+ * guaranteed failure. Matches `STREAM_TIMEOUT_MS` in the CLI's chat command
+ * (src/cli/src/commands/chat.ts), which already allowed 10 minutes; mcplocal
+ * sitting in the middle with 30s was the binding constraint.
+ *
+ * Override with `MCPLOCAL_LONG_TIMEOUT_MS`.
+ */
+export const LONG_RUNNING_TIMEOUT_MS = Number(process.env['MCPLOCAL_LONG_TIMEOUT_MS']) || 600_000;
+
 /**
  * Discovery-class operations (tools/list, resources/list, prompts/list) should not share
  * the full tool-call timeout budget — a single dead upstream would stall session init for
@@ -121,9 +153,7 @@ export class McpdClient {
     try {
       res = await fetch(url, init);
     } catch (err: unknown) {
-      if (err instanceof DOMException && err.name === 'TimeoutError') {
-        throw new ConnectionError(this.baseUrl, new Error(`Request timed out after ${this.timeoutMs}ms`));
-      }
+      if (isTimeout(err)) throw new UpstreamTimeoutError(this.baseUrl, this.timeoutMs);
       throw new ConnectionError(this.baseUrl, err);
     }
 
@@ -131,7 +161,18 @@ export class McpdClient {
       throw new AuthenticationError();
     }
 
-    const text = await res.text();
+    // The body read MUST be inside a try. mcpd writes SSE headers immediately
+    // on chat routes, so fetch() resolves long before the turn finishes and the
+    // abort lands here instead — previously escaping as a raw DOMException and
+    // surfacing to the user as an opaque `500 code:23`.
+    let text: string;
+    try {
+      text = await res.text();
+    } catch (err: unknown) {
+      if (isTimeout(err)) throw new UpstreamTimeoutError(this.baseUrl, this.timeoutMs);
+      throw new ConnectionError(this.baseUrl, err);
+    }
+
     let parsed: unknown;
     try {
       parsed = JSON.parse(text);
@@ -142,6 +183,51 @@ export class McpdClient {
     return { status: res.status, body: parsed };
   }
 
+  /**
+   * Forward a request and hand back the raw Response, body unread.
+   *
+   * `forward()` buffers through `res.text()`, which is fine for CRUD but
+   * defeats streaming entirely: an SSE chat arrives at the client as one blob
+   * after the turn ends, so the token-by-token output the CLI draws never
+   * appears. Streaming routes use this instead and pipe the body straight
+   * through.
+   */
+  async forwardStream(
+    method: string,
+    path: string,
+    query: string,
+    body: unknown | undefined,
+    authOverride?: string,
+  ): Promise<Response> {
+    const url = `${this.baseUrl}${path}${query ? `?${query}` : ''}`;
+    const headers: Record<string, string> = {
+      ...this.extraHeaders,
+      'Authorization': `Bearer ${authOverride ?? this.token}`,
+      // Accept both: mcpd picks SSE or JSON based on the request's `stream` flag.
+      'Accept': 'text/event-stream, application/json',
+    };
+
+    const init: RequestInit = {
+      method,
+      headers,
+      signal: AbortSignal.timeout(this.timeoutMs),
+    };
+    if (body !== undefined && body !== null && method !== 'GET' && method !== 'HEAD') {
+      headers['Content-Type'] = 'application/json';
+      init.body = JSON.stringify(body);
+    }
+
+    try {
+      const res = await fetch(url, init);
+      if (res.status === 401) throw new AuthenticationError();
+      return res;
+    } catch (err: unknown) {
+      if (err instanceof AuthenticationError) throw err;
+      if (isTimeout(err)) throw new UpstreamTimeoutError(this.baseUrl, this.timeoutMs);
+      throw new ConnectionError(this.baseUrl, err);
+    }
+  }
+
   private async request<T>(method: string, path: string, body?: unknown): Promise<T> {
     const result = await this.forward(method, path, '', body);
 

src/mcplocal/src/http/routes/proxy.ts

@@ -1,10 +1,62 @@
 /**
  * Catch-all proxy route that forwards /api/v1/* requests to mcpd.
  */
-import type { FastifyInstance } from 'fastify';
-import { AuthenticationError, ConnectionError } from '../mcpd-client.js';
+import { Readable } from 'node:stream';
+
+import type { FastifyInstance, FastifyReply } from 'fastify';
+
+import { AuthenticationError, ConnectionError, UpstreamTimeoutError, LONG_RUNNING_TIMEOUT_MS } from '../mcpd-client.js';
 import type { McpdClient } from '../mcpd-client.js';
 
+/**
+ * Routes that are expected to run long and/or stream.
+ *
+ * An agent turn is a multi-turn tool-use loop — minutes, not seconds — so the
+ * 30s default budget guarantees failure rather than guarding against it. These
+ * also stream SSE, which must be piped rather than buffered or the client sees
+ * one blob at the end instead of live output.
+ */
+const LONG_RUNNING = [
+  /^\/api\/v1\/agents\/[^/]+\/chat\b/,
+  /^\/api\/v1\/projects\/[^/]+\/chat\b/,
+  /^\/api\/v1\/llms\/[^/]+\/infer\b/,
+  /^\/api\/v1\/inference-tasks\/[^/]+\/stream\b/,
+];
+
+function isLongRunning(path: string): boolean {
+  return LONG_RUNNING.some((re) => re.test(path));
+}
+
+/** Headers worth preserving from mcpd; everything else is re-derived by Fastify. */
+const PASSTHROUGH_HEADERS = ['content-type', 'cache-control', 'x-accel-buffering'];
+
+function sendUpstreamError(reply: FastifyReply, err: unknown): FastifyReply | undefined {
+  if (err instanceof AuthenticationError) {
+    return reply.code(401).send({
+      error: 'unauthorized',
+      message: 'Authentication with mcpd failed. Run `mcpctl login` to refresh your token.',
+    });
+  }
+  if (err instanceof UpstreamTimeoutError) {
+    // 504, not 503 — mcpd was reachable, it just did not finish. Reporting this
+    // as "cannot reach mcpd" sent a previous debugging session chasing a
+    // network fault while /healthz answered in 32ms.
+    return reply.code(504).send({
+      error: 'upstream_timeout',
+      message:
+        `mcpd did not respond within ${String(err.timeoutMs)}ms. The daemon is reachable — the ` +
+        'request itself ran long. Raise MCPLOCAL_LONG_TIMEOUT_MS if this is a legitimately slow turn.',
+    });
+  }
+  if (err instanceof ConnectionError) {
+    return reply.code(503).send({
+      error: 'service_unavailable',
+      message: 'Cannot reach mcpd daemon. Is it running?',
+    });
+  }
+  return undefined;
+}
+
 export function registerProxyRoutes(app: FastifyInstance, client: McpdClient): void {
   app.all('/api/v1/*', async (request, reply) => {
     const path = (request.url.split('?')[0]) ?? '/';
@@ -19,25 +71,78 @@ export function registerProxyRoutes(app: FastifyInstance, client: McpdClient): v
     // Forward the user's auth token to mcpd so RBAC applies per-user.
     // If no user token is present, mcpd will use its auth hook to reject.
     const authHeader = request.headers['authorization'] as string | undefined;
-    const userToken = authHeader?.startsWith('Bearer ') ? authHeader.slice(7) : undefined;
+    const userToken = authHeader !== undefined && authHeader.startsWith('Bearer ')
+      ? authHeader.slice(7)
+      : undefined;
+
+    if (isLongRunning(path)) {
+      return proxyStreaming(reply, client, request.method, path, querystring, body, userToken);
+    }
 
     try {
       const result = await client.forward(request.method, path, querystring, body, userToken);
       return reply.code(result.status).send(result.body);
     } catch (err: unknown) {
-      if (err instanceof AuthenticationError) {
-        return reply.code(401).send({
-          error: 'unauthorized',
-          message: 'Authentication with mcpd failed. Run `mcpctl login` to refresh your token.',
-        });
-      }
-      if (err instanceof ConnectionError) {
-        return reply.code(503).send({
-          error: 'service_unavailable',
-          message: 'Cannot reach mcpd daemon. Is it running?',
-        });
-      }
+      const handled = sendUpstreamError(reply, err);
+      if (handled) return handled;
       throw err;
     }
   });
 }
+
+/**
+ * Pipe a long-running response straight through, headers and all.
+ *
+ * Hijacks the reply so Fastify does not try to serialize a stream, then copies
+ * mcpd's status and content-type before piping. `x-accel-buffering` matters:
+ * mcpd sets it to `no` so intermediaries don't buffer SSE, and dropping it here
+ * would reintroduce the exact stall we are fixing.
+ */
+async function proxyStreaming(
+  reply: FastifyReply,
+  client: McpdClient,
+  method: string,
+  path: string,
+  querystring: string,
+  body: unknown,
+  userToken: string | undefined,
+): Promise<void> {
+  const longClient = client.withTimeout(LONG_RUNNING_TIMEOUT_MS);
+
+  let res: Response;
+  try {
+    res = await longClient.forwardStream(method, path, querystring, body, userToken);
+  } catch (err: unknown) {
+    const handled = sendUpstreamError(reply, err);
+    if (handled) return;
+    throw err;
+  }
+
+  const headers: Record<string, string> = {};
+  for (const name of PASSTHROUGH_HEADERS) {
+    const value = res.headers.get(name);
+    if (value !== null) headers[name] = value;
+  }
+
+  reply.hijack();
+  reply.raw.writeHead(res.status, headers);
+
+  if (res.body === null) {
+    reply.raw.end();
+    return;
+  }
+
+  try {
+    // Node's Readable.fromWeb bridges the fetch ReadableStream onto the socket.
+    await new Promise<void>((resolve, reject) => {
+      const upstream = Readable.fromWeb(res.body as Parameters<typeof Readable.fromWeb>[0]);
+      upstream.on('error', reject);
+      reply.raw.on('close', () => { upstream.destroy(); resolve(); });
+      upstream.pipe(reply.raw).on('finish', resolve).on('error', reject);
+    });
+  } catch {
+    // Headers are already on the wire, so there is no status left to change.
+    // Close the socket; the client surfaces the truncated stream.
+    if (!reply.raw.writableEnded) reply.raw.end();
+  }
+}

src/mcplocal/src/index.ts

@@ -11,7 +11,7 @@ export type { MainResult } from './main.js';
 export { ProviderRegistry } from './providers/index.js';
 export type { LlmProvider, CompletionOptions, CompletionResult, ChatMessage } from './providers/index.js';
 export { OpenAiProvider, AnthropicProvider, OllamaProvider, GeminiCliProvider, DeepSeekProvider } from './providers/index.js';
-export { createHttpServer, loadHttpConfig, McpdClient, AuthenticationError, ConnectionError, registerProxyRoutes } from './http/index.js';
+export { createHttpServer, loadHttpConfig, McpdClient, AuthenticationError, ConnectionError, UpstreamTimeoutError, registerProxyRoutes } from './http/index.js';
 export type { HttpConfig, HttpServerDeps } from './http/index.js';
 export type {
   JsonRpcRequest,

src/mcplocal/tests/mcpd-client.test.ts

@@ -1,6 +1,6 @@
 import { describe, it, expect, afterAll, afterEach } from 'vitest';
 import http from 'node:http';
-import { McpdClient, ConnectionError } from '../src/http/mcpd-client.js';
+import { McpdClient, ConnectionError, UpstreamTimeoutError } from '../src/http/mcpd-client.js';
 
 /**
  * Create a local HTTP server for testing McpdClient behavior.
@@ -85,7 +85,7 @@ describe('McpdClient', () => {
 
   // ── Timeout behavior ──
 
-  it('times out on slow responses and throws ConnectionError', async () => {
+  it('times out on slow responses and throws UpstreamTimeoutError', async () => {
     const { server, url } = await createTestServer((_req, _res) => {
       // Never respond — simulates a hanging upstream tool call
     });
@@ -96,7 +96,7 @@ describe('McpdClient', () => {
 
     const start = Date.now();
     await expect(client.post('/api/v1/mcp/proxy', { serverId: 's1' })).rejects.toThrow(
-      /timed out/,
+      /did not respond within/,
     );
     const elapsed = Date.now() - start;
 
@@ -105,7 +105,7 @@ describe('McpdClient', () => {
     expect(elapsed).toBeLessThan(3000);
   });
 
-  it('timeout error is a ConnectionError with descriptive message', async () => {
+  it('timeout is NOT a ConnectionError — a slow daemon is not an absent one', async () => {
     const { server, url } = await createTestServer((_req, _res) => {
       // Never respond
     });
@@ -117,8 +117,12 @@ describe('McpdClient', () => {
       await client.get('/test');
       expect.unreachable('Should have thrown');
     } catch (err) {
-      expect(err).toBeInstanceOf(ConnectionError);
-      expect((err as Error).message).toContain('Request timed out after 200ms');
+      // Reporting a timeout as "cannot connect" is what sent a previous
+      // debugging session chasing a network fault that did not exist.
+      expect(err).toBeInstanceOf(UpstreamTimeoutError);
+      expect(err).not.toBeInstanceOf(ConnectionError);
+      expect((err as UpstreamTimeoutError).timeoutMs).toBe(200);
+      expect((err as Error).message).toContain('did not respond within 200ms');
     }
   });
 
@@ -146,7 +150,7 @@ describe('McpdClient', () => {
     const derived = client.withHeaders({ 'X-Custom': 'val' });
 
     const start = Date.now();
-    await expect(derived.get('/test')).rejects.toThrow(/timed out/);
+    await expect(derived.get('/test')).rejects.toThrow(/did not respond within/);
     const elapsed = Date.now() - start;
     expect(elapsed).toBeLessThan(2000);
   });

src/mcplocal/tests/proxy-long-running.test.ts

@@ -0,0 +1,255 @@
+import http from 'node:http';
+
+import Fastify, { type FastifyInstance } from 'fastify';
+import { describe, it, expect, afterEach } from 'vitest';
+
+import {
+  McpdClient,
+  UpstreamTimeoutError,
+  ConnectionError,
+  LONG_RUNNING_TIMEOUT_MS,
+  DEFAULT_TIMEOUT_MS,
+} from '../src/http/mcpd-client.js';
+import { registerProxyRoutes } from '../src/http/routes/proxy.js';
+
+/**
+ * Regression cover for the 30s proxy timeout that made `mcpctl chat` fail with
+ * a misleading "Cannot reach mcpd daemon" 503 while mcpd was answering
+ * /healthz in 32ms.
+ *
+ * Three separate defects are pinned here:
+ *   1. chat routes inherited the 30s CRUD budget, so any turn longer than 30s
+ *      failed — and an agent turn is a tool-use loop that routinely exceeds it;
+ *   2. a timeout was reported as a connection failure, sending diagnosis after
+ *      a network fault that did not exist;
+ *   3. SSE was buffered through res.text(), so streaming never reached the
+ *      client even when the turn finished in time.
+ */
+let app: FastifyInstance | null = null;
+let upstream: FastifyInstance | null = null;
+
+afterEach(async () => {
+  if (app) { await app.close(); app = null; }
+  if (upstream) { await upstream.close(); upstream = null; }
+});
+
+/** A stand-in mcpd. Returns its base URL. */
+async function startUpstream(register: (a: FastifyInstance) => void): Promise<string> {
+  upstream = Fastify();
+  register(upstream);
+  await upstream.listen({ port: 0, host: '127.0.0.1' });
+  const addr = upstream.server.address();
+  if (addr === null || typeof addr === 'string') throw new Error('no address');
+  return `http://127.0.0.1:${String(addr.port)}`;
+}
+
+async function startProxy(baseUrl: string, timeoutMs?: number): Promise<FastifyInstance> {
+  app = Fastify();
+  registerProxyRoutes(app, new McpdClient(baseUrl, 'test-token', {}, timeoutMs));
+  await app.ready();
+  return app;
+}
+
+describe('proxy — long-running route budget', () => {
+  it('gives chat routes the long budget, not the 30s CRUD default', () => {
+    // The constants themselves are the contract: a 30s cap on an agent turn is
+    // a guaranteed failure, not a safety net.
+    expect(DEFAULT_TIMEOUT_MS).toBe(30_000);
+    expect(LONG_RUNNING_TIMEOUT_MS).toBeGreaterThanOrEqual(600_000);
+  });
+
+  it('does not abort an agent chat that outlives the CRUD budget', async () => {
+    const base = await startUpstream((a) => {
+      a.post('/api/v1/agents/:name/chat', async () => {
+        // Longer than the (deliberately tiny) CRUD budget below. Before the
+        // fix this inherited that budget and 503'd.
+        await new Promise((r) => setTimeout(r, 250));
+        return { answer: 'pong' };
+      });
+    });
+    // CRUD budget of 50ms — a chat route must NOT inherit it.
+    const proxy = await startProxy(base, 50);
+
+    const res = await proxy.inject({
+      method: 'POST',
+      url: '/api/v1/agents/reviewer/chat',
+      payload: { message: 'hi' },
+    });
+
+    expect(res.statusCode).toBe(200);
+    expect(res.json()).toEqual({ answer: 'pong' });
+  });
+
+  it('still applies the short budget to ordinary CRUD routes', async () => {
+    const base = await startUpstream((a) => {
+      a.get('/api/v1/servers', async () => {
+        await new Promise((r) => setTimeout(r, 300));
+        return [];
+      });
+    });
+    const proxy = await startProxy(base, 50);
+
+    const res = await proxy.inject({ method: 'GET', url: '/api/v1/servers' });
+    // Times out — and is now reported honestly as a timeout, not a connection fault.
+    expect(res.statusCode).toBe(504);
+    expect(res.json().error).toBe('upstream_timeout');
+  });
+
+  it('reports a timeout as 504, never as "cannot reach mcpd"', async () => {
+    const base = await startUpstream((a) => {
+      a.get('/api/v1/servers', async () => {
+        await new Promise((r) => setTimeout(r, 300));
+        return [];
+      });
+    });
+    const proxy = await startProxy(base, 50);
+
+    const res = await proxy.inject({ method: 'GET', url: '/api/v1/servers' });
+    const body = res.json();
+    expect(body.message).toMatch(/did not respond within/);
+    expect(body.message).not.toMatch(/Cannot reach mcpd/);
+    expect(body.message).toMatch(/reachable/);
+  });
+
+  it('streams SSE through instead of buffering it', async () => {
+    const base = await startUpstream((a) => {
+      a.post('/api/v1/agents/:name/chat', async (_req, reply) => {
+        reply.raw.writeHead(200, {
+          'Content-Type': 'text/event-stream',
+          'Cache-Control': 'no-cache',
+          'X-Accel-Buffering': 'no',
+        });
+        reply.raw.write('data: {"type":"text","delta":"po"}\n\n');
+        reply.raw.write('data: {"type":"text","delta":"ng"}\n\n');
+        reply.raw.write('data: [DONE]\n\n');
+        reply.raw.end();
+        return reply;
+      });
+    });
+    const proxy = await startProxy(base, 50);
+
+    const res = await proxy.inject({
+      method: 'POST',
+      url: '/api/v1/agents/reviewer/chat',
+      payload: { message: 'hi', stream: true },
+    });
+
+    expect(res.statusCode).toBe(200);
+    // Content-type must survive — a client that gets application/json will not
+    // parse the event stream.
+    expect(res.headers['content-type']).toMatch(/text\/event-stream/);
+    // x-accel-buffering=no must survive too, or intermediaries re-buffer the
+    // stream and reintroduce the stall.
+    expect(res.headers['x-accel-buffering']).toBe('no');
+    expect(res.body).toContain('"delta":"po"');
+    expect(res.body).toContain('"delta":"ng"');
+    expect(res.body).toContain('[DONE]');
+  });
+
+  it('delivers each SSE frame while the upstream is still generating', async () => {
+    // The buffering regression is invisible to the pass-through test above:
+    // `inject()` collects the whole body, so a proxy that buffers via
+    // res.text() still passes it. This test proves *progressive* delivery by
+    // making the upstream withhold its final frame until the client has
+    // observed the first one. A buffering proxy can never satisfy that
+    // ordering — the 3s guard resolves the gate so the run fails cleanly
+    // instead of deadlocking.
+    let openGate: (seen: boolean) => void = () => {};
+    const clientSawFirstFrame = new Promise<boolean>((r) => { openGate = r; });
+    const guard = setTimeout(() => openGate(false), 3_000);
+
+    const base = await startUpstream((a) => {
+      a.post('/api/v1/agents/:name/chat', async (_req, reply) => {
+        reply.raw.writeHead(200, { 'Content-Type': 'text/event-stream' });
+        reply.raw.write('data: {"type":"text","delta":"live"}\n\n');
+        await clientSawFirstFrame;
+        reply.raw.write('data: {"type":"final"}\n\n');
+        reply.raw.write('data: [DONE]\n\n');
+        reply.raw.end();
+        return reply;
+      });
+    });
+    const proxy = await startProxy(base, 50);
+    await proxy.listen({ port: 0, host: '127.0.0.1' });
+    const addr = proxy.server.address();
+    if (addr === null || typeof addr === 'string') throw new Error('no address');
+
+    const body = await new Promise<string>((resolve, reject) => {
+      const req = http.request({
+        hostname: '127.0.0.1',
+        port: addr.port,
+        path: '/api/v1/agents/reviewer/chat',
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+      }, (res) => {
+        let acc = '';
+        res.setEncoding('utf-8');
+        res.on('data', (chunk: string) => {
+          acc += chunk;
+          if (acc.includes('"delta":"live"')) openGate(true);
+        });
+        res.on('end', () => resolve(acc));
+        res.on('error', reject);
+      });
+      req.on('error', reject);
+      req.end(JSON.stringify({ message: 'hi', stream: true }));
+    });
+    clearTimeout(guard);
+
+    // The ordering proof: the first frame reached the client while the
+    // upstream was still holding the stream open.
+    await expect(clientSawFirstFrame).resolves.toBe(true);
+    expect(body).toContain('"type":"final"');
+    expect(body).toContain('[DONE]');
+  });
+
+  it('relays a non-200 status from a streaming route', async () => {
+    const base = await startUpstream((a) => {
+      a.post('/api/v1/agents/:name/chat', async (_req, reply) => {
+        return reply.code(404).send({ error: 'Agent not found' });
+      });
+    });
+    const proxy = await startProxy(base, 50);
+
+    const res = await proxy.inject({
+      method: 'POST',
+      url: '/api/v1/agents/ghost/chat',
+      payload: { message: 'hi' },
+    });
+    expect(res.statusCode).toBe(404);
+    expect(res.body).toContain('Agent not found');
+  });
+
+  it('still reports a genuinely unreachable daemon as 503', async () => {
+    // Port 1 is reserved and refuses instantly.
+    const proxy = await startProxy('http://127.0.0.1:1', 500);
+    const res = await proxy.inject({ method: 'GET', url: '/api/v1/servers' });
+
+    expect(res.statusCode).toBe(503);
+    expect(res.json().error).toBe('service_unavailable');
+  });
+
+  it('propagates 401 from a streaming route so login guidance still fires', async () => {
+    const base = await startUpstream((a) => {
+      a.post('/api/v1/agents/:name/chat', async (_req, reply) => reply.code(401).send({}));
+    });
+    const proxy = await startProxy(base, 50);
+
+    const res = await proxy.inject({
+      method: 'POST',
+      url: '/api/v1/agents/reviewer/chat',
+      payload: { message: 'hi' },
+    });
+    expect(res.statusCode).toBe(401);
+    expect(res.json().message).toMatch(/mcpctl login/);
+  });
+});
+
+describe('error taxonomy', () => {
+  it('keeps timeout and unreachable as distinct types', () => {
+    const timeout = new UpstreamTimeoutError('http://mcpd', 30_000);
+    expect(timeout).not.toBeInstanceOf(ConnectionError);
+    expect(timeout.timeoutMs).toBe(30_000);
+    expect(timeout.message).toMatch(/did not respond within 30000ms/);
+  });
+});

src/mcplocal/tests/smoke/agent-chat.smoke.test.ts

@@ -18,8 +18,12 @@ import { describe, it, expect, beforeAll, afterAll } from 'vitest';
 import http from 'node:http';
 import https from 'node:https';
 import { spawnSync, execSync } from 'node:child_process';
+import { existsSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { homedir } from 'node:os';
 
 const MCPD_URL = process.env.MCPD_URL ?? 'https://mcpctl.ad.itaz.eu';
+const MCPLOCAL_URL = process.env.MCPLOCAL_URL ?? 'http://localhost:3200';
 const LLM_URL = process.env.MCPCTL_SMOKE_LLM_URL;
 const LLM_MODEL = process.env.MCPCTL_SMOKE_LLM_MODEL ?? 'qwen3-thinking';
 const LLM_KEY = process.env.MCPCTL_SMOKE_LLM_KEY;
@@ -27,6 +31,10 @@ const SUFFIX = Date.now().toString(36);
 const SECRET_NAME = `smoke-chat-sec-${SUFFIX}`;
 const LLM_NAME = `smoke-chat-llm-${SUFFIX}`;
 const AGENT_NAME = `smoke-chat-agent-${SUFFIX}`;
+// Dedicated agent for the streaming-timing test: the shared agent's system
+// prompt pins the reply to a single token, which is too short to distinguish
+// live streaming from an end-of-turn buffer dump.
+const STREAM_AGENT_NAME = `smoke-stream-agent-${SUFFIX}`;
 
 interface CliResult { code: number; stdout: string; stderr: string }
 
@@ -99,6 +107,7 @@ describe('agent chat smoke (live LLM)', () => {
   afterAll(() => {
     if (!liveLlmConfigured || !mcpdUp) return;
     run(`delete agent ${AGENT_NAME}`);
+    run(`delete agent ${STREAM_AGENT_NAME}`);
     run(`delete llm ${LLM_NAME}`);
     run(`delete secret ${SECRET_NAME}`);
   });
@@ -139,6 +148,92 @@ describe('agent chat smoke (live LLM)', () => {
     expect(result.stderr).toMatch(/thread:\s+c[a-z0-9]+/);
   });
 
+  it('streams progressively THROUGH mcplocal — frames arrive during generation, not in one burst', async () => {
+    if (!liveLlmConfigured || !mcpdUp) return;
+    // The regression this pins: mcplocal's /api/v1/* proxy buffered SSE via
+    // res.text(), so the CLI showed nothing until the turn finished and then
+    // dumped the whole answer at once. The --direct tests above bypass
+    // mcplocal entirely and cannot catch that. This one posts to the local
+    // proxy (the path `mcpctl chat` actually takes) and asserts frames are
+    // spread across the generation window: with buffering, everything lands
+    // within a few ms of stream end.
+    if (!(await healthz(MCPLOCAL_URL))) {
+      // eslint-disable-next-line no-console
+      console.warn(`\n  ○ mcplocal streaming smoke: skipped — ${MCPLOCAL_URL}/healthz unreachable.\n`);
+      return;
+    }
+    let token = '';
+    try {
+      const credsPath = join(homedir(), '.mcpctl', 'credentials');
+      if (existsSync(credsPath)) {
+        const creds = JSON.parse(readFileSync(credsPath, 'utf-8')) as { token?: string };
+        if (creds.token !== undefined) token = creds.token;
+      }
+    } catch { /* unauthenticated — the request will 401 and fail loudly */ }
+
+    run(`delete agent ${STREAM_AGENT_NAME}`);
+    const agent = run([
+      `create agent ${STREAM_AGENT_NAME}`,
+      `--llm ${LLM_NAME}`,
+      `--description "mcplocal streaming smoke"`,
+      `--system-prompt "You are a smoke test. Follow the user's instructions exactly."`,
+      '--default-temperature 0',
+      '--default-max-tokens 512',
+    ].join(' '));
+    expect(agent.code, agent.stderr).toBe(0);
+
+    const url = new URL(`${MCPLOCAL_URL.replace(/\/$/, '')}/api/v1/agents/${STREAM_AGENT_NAME}/chat`);
+    const deltaTimes: number[] = [];
+    let endTime = 0;
+    let status = 0;
+    let raw = '';
+
+    await new Promise<void>((resolve, reject) => {
+      const req = http.request({
+        hostname: url.hostname,
+        port: url.port || 80,
+        path: url.pathname,
+        method: 'POST',
+        timeout: 120_000,
+        headers: {
+          'Content-Type': 'application/json',
+          ...(token !== '' ? { Authorization: `Bearer ${token}` } : {}),
+        },
+      }, (res) => {
+        status = res.statusCode ?? 0;
+        res.setEncoding('utf-8');
+        let buf = '';
+        res.on('data', (chunk: string) => {
+          raw += chunk;
+          buf += chunk;
+          let nl: number;
+          while ((nl = buf.indexOf('\n\n')) !== -1) {
+            const frame = buf.slice(0, nl);
+            buf = buf.slice(nl + 2);
+            if (/"type":"(text|thinking)"/.test(frame)) deltaTimes.push(Date.now());
+          }
+        });
+        res.on('end', () => { endTime = Date.now(); resolve(); });
+        res.on('error', reject);
+      });
+      req.on('error', reject);
+      req.on('timeout', () => { req.destroy(); reject(new Error('stream timed out')); });
+      req.end(JSON.stringify({
+        message: 'Count from 1 to 40, one number per line. No other text.',
+        stream: true,
+        max_tokens: 400,
+      }));
+    });
+
+    expect(status, raw.slice(0, 500)).toBe(200);
+    expect(deltaTimes.length).toBeGreaterThanOrEqual(2);
+    // The buffering signature: every frame lands in the same final burst as
+    // stream end. Live streaming puts the first delta well before the end —
+    // a 40-line generation spans seconds; 300ms is a conservative floor.
+    const firstDelta = deltaTimes[0]!;
+    expect(endTime - firstDelta).toBeGreaterThanOrEqual(300);
+  }, 150_000);
+
   it('streaming `mcpctl chat` emits text deltas', () => {
     if (!liveLlmConfigured || !mcpdUp) return;
     // Default mode is streaming. Pipe stdout/stderr separately.