child_process via require(): null bytes in file/args are not validated — 'spawn /bin/true UNKNOWN' instead of ERR_INVALID_ARG_VALUE; the named-import path validates with a non-node message

[proggeramlug]

Found through the MCP debug logs that #9491 unlocked (#9500 / #9531): the harness's null-byte case (E62_mcp_add_json_unicode, a server arg containing \x00) logs

node : Connection failed after 0ms: The argument 'args[1]' must be a string without null bytes. Received 'a\x00b'
perry: Connection failed after 1ms: spawn /bin/true UNKNOWN

Two paths, two behaviours (the #9485 family again)

import { createRequire } from "node:module";
const cp: any = createRequire(import.meta.url)("child_process");   // cross-spawn's / the MCP SDK's shape
cp.spawn("/bin/true", ["a\x00b"]);          // perry: returns a ChildProcess, then 'error' UNKNOWN "spawn /bin/true UNKNOWN"
cp.spawn("/bin/tr\x00ue", []);              // perry: 'error' UNKNOWN "spawn /bin/tr ue UNKNOWN"
cp.spawnSync("/bin/true", ["a\x00b"]);      // perry: returns a result object
cp.execFile("/bin/true", ["a\x00b"], cb);   // perry: cb(err) with code UNKNOWN

Node throws synchronously from all four, ERR_INVALID_ARG_VALUE, message The argument 'args[0]' must be a string without null bytes. Received 'a\x00b' (or 'file' for the command). Perry's CJS-default-namespace path performs no validation, hands the string to the OS, and reports the CString failure as UNKNOWN.

The named-import path (import { spawn, spawnSync } from "node:child_process") does validate — it throws ERR_INVALID_ARG_VALUE synchronously — but with a different message:

node : "The argument 'args[0]' must be a string without null bytes. Received 'a\\x00b'"
perry: "The argument must not contain null bytes"

So: (1) the validation lives on one lowering path and not the other — the dispatch-router / CJS-namespace path (#9498 made these calls reachable) skips it; the check belongs in the runtime entry points (js_child_process_spawn_streams, js_child_process_spawn_sync, js_child_process_exec_file, and exec's command) so every spelling shares it; (2) the message should name the argument ('file', 'args[i]', 'options.cwd', 'options.env'...) and echo the received value with \x00 escaping, as node's validateArgumentNullCheck does.

Byte-compare bar: both scripts above print node's lines under node --experimental-strip-types.

[proggeramlug]

Closing: fixed in #9568 (child-process null-byte validation on the require() path), landed via merge train #9572 on 2026-09-02.