fix(cli): escape codex args and stop aborting on exit in launch-codex

[sumanxg]

Problem

launch-codex spawns codex.cmd with shell: true on Windows, so Node joins argv with plain spaces and no escaping (the DEP0190 warning). This is the same defect fixed for launch in #8837, which disclosed it here but left it unfixed.

It is worse for launch-codex than for launch: it breaks every Windows invocation, not only the ones with a multi-word user argument, because buildCodexProviderArgs() injects -c flags whose TOML values are quoted. Captured through a probe .cmd shim that forwards %* exactly like the real npm shim:

["-c","model_provider=omniroute",
 "-c","model_providers.omniroute.name=OmniRoute",
 "-c","model_providers.omniroute.base_url=http://localhost:20128/v1",
 "-c","model_providers.omniroute.env_key=OMNIROUTE_API_KEY",
 "-c","model_providers.omniroute.wire_api=responses",
 "-c","model_providers.omniroute.requires_openai_auth=false",
 "fix","the","bug"]

Three separate corruptions:

1. cmd.exe strips the TOML quotes, so model_provider="omniroute" reaches codex as model_provider=omniroute and no longer parses as a TOML string.
2. A multi-word pass-through argument (fix the bug & ship it) is split into separate argv entries.
3. Everything after an unquoted & is swallowed — cmd.exe reads it as a command separator.

Second defect, also ported from #8837: process.exit(exitCode) in the command action aborts with the libuv !(handle->flags & UV_HANDLE_CLOSING) assertion (async.c:94, exit 0xC0000409) on any non-zero child exit, because it tears the loop down while the inherited stdio handles of the just-exited child are still closing.

Fix

• Extract the escaping helper from launch.mjs into bin/cli/utils/winShellArgs.mjs and reuse it from both launchers, instead of duplicating a subtle two-layer escape. quoteClaudeArgs keeps its signature and behaviour.
• launch-codex.mjs: quote the whole codex argv (provider flags + profile + pass-through args) on the win32 shell path via the new quoteCodexArgs. Off Windows there is no shell, so argv is passed through untouched.
• launch-codex.mjs: process.exit() → process.exitCode, letting the loop drain.

Validation

tests/unit/cli/launch-codex-windows-spawn-args.test.ts, mirroring the launch test added in #8837:

• golden strings pin the exact win32 encoding, including the double caret-escape the .cmd shim's %* re-parse requires — the cmd.exe round-trip is Windows-only and skips on Linux CI, so without goldens CI would guard nothing;
• a real cmd.exe round-trip through a probe .cmd asserts the child argv is byte-identical to what the caller passed, using the actual buildCodexProviderArgs() output plus quotes, ampersands, pipes, %PATH%, ^, !, a trailing backslash and an empty argument.

Run on Windows 11 / Node 24.18.0:

node --import tsx/esm --test tests/unit/cli/launch-codex-windows-spawn-args.test.ts \
  tests/unit/cli/launch-codex.test.ts tests/unit/cli/launch-windows-spawn-args.test.ts \
  tests/unit/cli/launch-command.test.ts
# tests 23 | pass 23 | fail 0