From 5401e527e6878034d95274dd45fc1454255432dd Mon Sep 17 00:00:00 2001
From: cliffhall <cliff@futurescale.com>
Date: Thu, 6 Aug 2026 09:52:40 -0400
Subject: [PATCH] fix: handle spawn failure of the MCP test server in
 smoke:web:app
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Copilot's third pass (suppressed comment) caught the remaining hole in the
child-process handling: `spawn()` reports a failure to start via an `error`
event, not `exit`. With no `error` listener Node throws it uncaught, replacing
the smoke's diagnostic with a raw stack — and because `exit` never fires in that
case, the readiness poll would otherwise spin for the full 30s before reporting
a timeout that misattributes the cause. `close` is now listened to alongside
`exit` for the same reason: it fires in cases `exit` does not.

prod-web-server.mjs already documents this exact hazard for the launcher child;
this brings the test-server child in line.

Both new branches verified by hand:
  - unspawnable executable → "could not spawn the MCP test server (…): spawn
    /nonexistent/node-binary ENOENT", immediately, instead of an uncaught throw
  - missing module → "MCP test server exited early" with the loader stack, fast,
    with no 30s hang

Full `npm run ci` green.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAR2Nr9kXbrywFNUVoTe9F
---
 scripts/smoke-web-app.mjs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/scripts/smoke-web-app.mjs b/scripts/smoke-web-app.mjs
index 261663c0..73ca5f03 100644
--- a/scripts/smoke-web-app.mjs
+++ b/scripts/smoke-web-app.mjs
@@ -166,12 +166,25 @@ async function startMcpServer() {
   child.stdout.on("data", (d) => (out += d));
   child.stderr.on("data", (d) => (out += d));
   let exited = false;
+  let spawnError = null;
+  // A spawn failure (e.g. an unbuilt/renamed entry) emits `error`, NOT `exit` —
+  // and with no `error` listener Node throws it uncaught, replacing this smoke's
+  // diagnostic with a raw stack. `close` is listened to alongside `exit` for the
+  // same reason: it fires in cases `exit` does not, so a child that dies without
+  // an exit event can't leave the poll below spinning for the full 30s.
+  child.on("error", (err) => (spawnError = err));
   child.on("exit", () => (exited = true));
+  child.on("close", () => (exited = true));
 
   for (let attempt = 0; attempt < 120; attempt++) {
     // Take the port the server actually bound, not the one we asked for.
     const announced = out.match(/listening at (http:\/\/\S+)/i);
     if (announced) return { child, url: announced[1] };
+    if (spawnError) {
+      throw new Error(
+        `could not spawn the MCP test server (${composableServer}): ${spawnError.message}`,
+      );
+    }
     if (exited) throw new Error(`MCP test server exited early:\n${out}`);
     await delay(250);
   }