fix(engines): stop a nested moshcode child opening a second TUI

A CLI verb called from a script (run(), install(), agents(), upgrade())
spawns `moshcode <verb>` with stdio inherited, so the child sees a TTY
whenever a human runs the script from a terminal. At the end of the verb
the child called backToPit(), printed the banner and blocked on its own
`mosh >` prompt, so the parent script never resumed.

Mark spawned children with MOSHCODE_NESTED=1 and treat that like a
non-TTY in backToPit, so a nested run exits and hands control back.
Same fix for the moshscript shim, which made an executable .mosh file
land in a TUI instead of returning to the user's shell.

Author: clawedassistant26

bin/moshcode.mjs

@@ -56,7 +56,10 @@ function parseMax(value) {
 // interactive. Piped / non-TTY invocations (scripts, CI, `… | moshcode run -`)
 // keep the old behaviour: exit with the child's code.
 function backToPit(label, code, signal) {
-  if (!process.stdin.isTTY) process.exit(code ?? 0);
+  // A nested invocation (moshscript shim, or a CLI verb called from a script)
+  // must hand control back to its parent, not open a second mosh pit on the
+  // shared TTY.
+  if (!process.stdin.isTTY || process.env.MOSHCODE_NESTED === "1") process.exit(code ?? 0);
   const how = signal ? ` (${signal})` : code != null ? ` (code ${code})` : "";
   console.log(`\n↩ ${label} exited${how} — back in the mosh pit. /quit to leave.\n`);
   return tui();

bin/moshscript.mjs

@@ -14,7 +14,10 @@ import { fileURLToPath } from "node:url";
 const BIN = fileURLToPath(new URL("moshcode.mjs", import.meta.url));
 const args = process.argv.slice(2); // everything after `moshscript`
 
-const child = spawn(process.execPath, [BIN, "run", ...args], { stdio: "inherit" });
+const child = spawn(process.execPath, [BIN, "run", ...args], {
+  stdio: "inherit",
+  env: { ...process.env, MOSHCODE_NESTED: "1" },
+});
 child.on("error", (e) => { console.error(`moshscript: ${e.message}`); process.exit(1); });
 child.on("exit", (code, signal) => {
   if (signal) {

src/cli.mjs

@@ -41,7 +41,10 @@ export function runMoshcode(cmd, args, ctx) {
   }
 
   ctx.out(`  ▶ ${printable}`);
-  const res = spawnSync(process.execPath, [MOSHCODE_BIN, ...argv], { stdio: "inherit" });
+  const res = spawnSync(process.execPath, [MOSHCODE_BIN, ...argv], {
+    stdio: "inherit",
+    env: { ...process.env, MOSHCODE_NESTED: "1" },
+  });
   if (res.error) throw res.error; // truly fatal: spawn itself failed (ENOENT etc.)
 
   const code = res.status ?? 1;

test/run-options.test.mjs

@@ -49,6 +49,21 @@ test("run accepts equals-form max option", async () => {
   assert.match(result.stdout, /1 loop\(s\)/);
 });
 
+test("run() marks the nested moshcode child as nested", async () => {
+  const dir = mkdtempSync(join(tmpdir(), "moshcode-nested-"));
+  const child = join(dir, "child.mosh");
+  const parent = join(dir, "parent.mosh");
+  writeFileSync(child, 'shell("echo NESTEDVAL=$MOSHCODE_NESTED");\n');
+  writeFileSync(parent, `run(${JSON.stringify(child)});\n`);
+
+  const result = await run([parent]);
+
+  assert.equal(result.status, 0);
+  // Without MOSHCODE_NESTED the child drops into its own TUI on a shared TTY
+  // instead of returning control to the parent script.
+  assert.match(result.stdout, /NESTEDVAL=1/);
+});
+
 test("run() includes another .mosh file, in order", async () => {
   const dir = mkdtempSync(join(tmpdir(), "moshcode-include-"));
   const child = join(dir, "child.mosh");