@@ -0,0 +1,11 @@
+---
+'@objectstack/cli': patch
+---
+
+Clause-②: no
+
+fix(cli): `os start` with the stdio MCP transport answers the `initialize` an MCP client writes when it spawns the server, and boots the configured app
+
+- **What was wrong.** An MCP client writes `initialize` to the server's stdin as soon as it spawns it. `os start` hands its stdin down to the processes it starts, and the CLI's argument parser fills an omitted positional argument from a pending stdin line. So the client's `initialize` became a config path. In a project with no `dist/objectstack.json`, the automatic compile step failed with `Config file not found: …/{"jsonrpc":"2.0",…}` and `os start` exited 1. In a project with a compiled artifact, the server printed `No objectstack.config.ts found — booting from artifact`, booted without the config's own plugins, and never answered `initialize`.
+- **What changed.** The automatic compile step now gets no stdin, and `os start` names the config path when it starts `os serve` (the same `objectstack.config.ts` in the working directory that `os serve` used by default). The client's first message stays in the pipe for the stdio transport, and the config is loaded.
+- **Unchanged:** the flags and environment variables of `os start`, `os serve` and `os compile`, and which config and artifact a boot uses.
@@ -240,10 +240,19 @@ export default class Start extends Command {
       const outputPath = path.resolve(cwd, CONVENTIONAL_ARTIFACT_RELATIVE_PATH);
       printStep('Compiling objectstack.config.ts → dist/objectstack.json...');
       const binPath = process.argv[1];
+      // ── stdin belongs to the protocol, never to the compile step (#24002) ──
+      // This command's stdin is the stdio MCP transport's input once the
+      // `serve` child below starts it, and an MCP client writes `initialize`
+      // the moment it spawns `os start` — before this one-shot child runs.
+      // Inherited, the child's argument parser read that pending line as its
+      // missing `config` positional (oclif's `tryStdin`), so the compile failed
+      // on "Config file not found: …/{"jsonrpc":"2.0",…}" and `initialize` was
+      // consumed before any transport existed. The compile reads no input, so
+      // it gets none: `'ignore'` keeps every byte in the pipe for `serve`.
       const compileResult = spawnSync(
         process.execPath,
         [binPath, 'compile', '--output', outputPath],
-        { stdio: 'inherit', env: process.env },
+        { stdio: ['ignore', 'inherit', 'inherit'], env: process.env },
       );
       if (compileResult.status !== 0) {
         printError('Compile failed — fix errors above before starting the server');
@@ -487,11 +496,25 @@ export default class Start extends Command {
         // `const child = spawn(` is the anchor
         // `utils/port-contract-single-source.test.ts` reads to hold the port
         // door above AHEAD of this spawn — keep the spelling.
+        //
+        // ── The config positional is NAMED, never left to stdin (#24002) ──
+        // stdio stays inherited: the child's stdio MCP transport reads this
+        // process's stdin. But oclif fills an omitted positional from a pending
+        // stdin line (`tryStdin`), and `serve`'s `config` is one — so with no
+        // positional here, an MCP client's `initialize`, written at spawn,
+        // became "the config path": the child booted without the config the
+        // banner above names ("No objectstack.config.ts found") and the
+        // transport never saw `initialize`. A supplied positional skips that
+        // read. `projectConfigPath` is the path `serve` would default to
+        // (`objectstack.config.ts` under this same cwd), and the same one the
+        // `Config:` row was judged by, so whether it joins the boot is still
+        // the child's own `cwdConfigJoinsBoot` reading — exactly as before.
         const child = spawn(
           process.execPath,
           [
             binPath,
             'serve',
+            projectConfigPath,
             flags.ui ? '--ui' : '--no-ui',
             ...(flags.verbose ? ['--verbose'] : []),
             ...(flags['log-level'] ? ['--log-level', flags['log-level']] : []),