Fix dev server port conflicts across worktrees

Running multiple worktrees in parallel (Conductor or plain git worktree)
caused studios on 5174/5175 to silently proxy to the first worktree's
API on :3001, serving stale code from the wrong branch.

A root orchestrator (scripts/dev.mjs) now picks a free port and threads
PORT + API_PROXY_TARGET into the api/studio children via env vars. The
vite proxy reads API_PROXY_TARGET with a :3001 fallback so solo dev and
prod builds are unaffected. Port-probe helper adapted from the
findFreePort in zig/electron.

Author: Eliezir

apps/studio/vite.config.ts

@@ -26,7 +26,7 @@ export default defineConfig({
     open: true,
     proxy: {
       "/api": {
-        target: "http://localhost:3001",
+        target: process.env.API_PROXY_TARGET ?? "http://localhost:3001",
         changeOrigin: true,
       },
     },

package.json

@@ -12,7 +12,7 @@
     "typecheck": "tsc --build",
     "lint": "eslint",
     "build": "tsc --build",
-    "dev": "pnpm --parallel --filter @adt/api --filter @adt/studio dev",
+    "dev": "node scripts/dev.mjs",
     "dev:api": "pnpm --filter @adt/api dev",
     "dev:studio": "pnpm --filter @adt/studio dev",
     "dev:desktop": "pnpm --filter @adt/desktop dev",

scripts/dev.mjs

@@ -0,0 +1,37 @@
+import { spawn } from "node:child_process"
+import { findFreePort } from "./find-free-port.mjs"
+
+const apiPort = await findFreePort({ start: 3001 })
+if (!apiPort) {
+  console.error("[dev] could not find a free port for the API in 3001-49151")
+  process.exit(1)
+}
+
+const proxyTarget = `http://localhost:${apiPort}`
+console.log(`[dev] API port: ${apiPort}`)
+console.log(`[dev] Studio proxy target: ${proxyTarget}`)
+
+const child = spawn(
+  "pnpm",
+  ["--parallel", "--filter", "@adt/api", "--filter", "@adt/studio", "dev"],
+  {
+    stdio: "inherit",
+    shell: process.platform === "win32",
+    env: {
+      ...process.env,
+      PORT: String(apiPort),
+      API_PROXY_TARGET: proxyTarget,
+    },
+  },
+)
+
+const forward = (signal) => () => {
+  if (!child.killed) child.kill(signal)
+}
+process.on("SIGINT", forward("SIGINT"))
+process.on("SIGTERM", forward("SIGTERM"))
+
+child.on("exit", (code, signal) => {
+  if (signal) process.kill(process.pid, signal)
+  else process.exit(code ?? 0)
+})

scripts/find-free-port.mjs

@@ -0,0 +1,23 @@
+import { createServer } from "node:net"
+
+function canListenOnPort(port) {
+  return new Promise((resolve) => {
+    const server = createServer()
+    server.once("error", () => resolve(false))
+    server.once("listening", () => server.close(() => resolve(true)))
+    server.listen(port)
+  })
+}
+
+export async function findFreePort({ start = 3001, end = 49151, maxAttempts = 200 } = {}) {
+  const limit = Math.min(maxAttempts, end - start + 1)
+  for (let i = 0; i < limit; i++) {
+    const port = start + i
+    if (await canListenOnPort(port)) return port
+  }
+  return undefined
+}
+
+export async function portTaken(port) {
+  return !(await canListenOnPort(port))
+}