Failed to parse the request body as JSON: client_metadata.x-codex-installation-id: EOF while parsing a string

## Bug Report

Version: v0.129.0-alpha.14 (Windows Store: 26.429.8261.0)
Platform: Windows 10 x64

## Error

Every request fails with:
Failed to parse the request body as JSON: client_metadata.x-codex-installation-id: EOF while parsing a string at line 3 column ~61000–331000

The column number grows proportionally to the number of installed skills/plugins.

## Root Cause

The request body size grows with each installed skill/plugin, even when set to enabled = false in config.toml. With the browser-use plugin enabled, the body reaches 300k+ bytes and gets truncated server-side.

## Steps to Reproduce

1. Install any skills (e.g. GitNexus, Image Gen, browser-use plugin)
2. Send any message in Codex
3. Error occurs immediately on every request

## Expected Behavior

• Skills/plugins set to enabled = false should not be injected into the request body
• Request body size should be bounded regardless of installed skills count
• The browser-use plugin (auto-enabled on upgrade to alpha.14) should not cause requests to exceed server limits

## Additional Notes

• Bug introduced after forced upgrade to v0.129.0-alpha.14 on 2026-05-07
• Clearing ~/.codex/.tmp, skills/, plugins/ temporarily reduces body size but Codex re-downloads on next launch
• Setting config.toml to read-only prevents re-enabling plugins but does not fix the injection issue