test: fix integration test timeouts by replacing inline tsx -e with proxy-runner script

Tests 1-2 were timing out because npx had to download tsx on cold start (not in
devDeps), blowing the 5s waitForResponses timeout before the subprocess was ready.
Also replaces fragile ESM import inside -e inline code with a proper file entrypoint.

Author: lewisnsmith

test/integration.test.ts

@@ -7,23 +7,21 @@ import { createInterface } from "node:readline";
 import type { LogEntry } from "../src/logger.js";
 
 const MOCK_SERVER = join(import.meta.dirname, "mock-mcp-server.ts");
-const PROXY_MODULE = join(import.meta.dirname, "..", "src", "proxy.ts");
+const PROXY_RUNNER = join(import.meta.dirname, "proxy-runner.ts");
 
 /**
  * Spawns a proxy process that wraps the mock MCP server,
  * sends JSON-RPC messages, and collects responses.
  */
 function createTestProxy(logDir: string) {
-  const child = spawn("npx", ["tsx", "-e", `
-    import { startProxy } from "${PROXY_MODULE.replace(/\\/g, "/")}";
-    process.env.FLIGHT_LOG_DIR = "${logDir.replace(/\\/g, "/")}";
-    startProxy({
-      command: "npx",
-      args: ["tsx", "${MOCK_SERVER.replace(/\\/g, "/")}"],
-      logDir: "${logDir.replace(/\\/g, "/")}",
-    });
-  `], {
+  const child = spawn("npx", ["tsx", PROXY_RUNNER], {
     stdio: ["pipe", "pipe", "pipe"],
+    env: {
+      ...process.env,
+      UPSTREAM_COMMAND: "npx",
+      UPSTREAM_ARGS: JSON.stringify(["tsx", MOCK_SERVER]),
+      LOG_DIR: logDir,
+    },
   });
 
   const responses: Array<Record<string, unknown>> = [];

test/proxy-runner.ts

@@ -0,0 +1,7 @@
+import { startProxy } from "../src/proxy.js";
+
+await startProxy({
+  command: process.env.UPSTREAM_COMMAND!,
+  args: JSON.parse(process.env.UPSTREAM_ARGS!),
+  logDir: process.env.LOG_DIR,
+});