error 400 'Instructions are not valid' after prompt.md change #3121

What version of Codex is running?

Building from main branch (commit 234c0a04)

Which model were you using?

gpt-5

What platform is your computer?

Windows x64

What steps can reproduce the bug?

1. Build Codex from main branch source
2. Run codex TUI
3. Send any message

What is the expected behavior?

Message should be processed normally

What do you see instead?

⚠️ stream error: unexpected status 400 Bad Request: {"detail":"Instructions are not valid"};

Additional information

Root cause: PR #3121 ("remove bold the keyword from prompt") removed line "- Bold the keyword, then colon + concise description." from codex-rs/core/prompt.md