## Why
`child_agents_md` is a disabled, under-development experiment that adds
a second model-visible explanation of hierarchical `AGENTS.md` behavior.
Keeping it leaves unused prompt, configuration, documentation, and test
surface.
## What changed
- remove the `ChildAgentsMd` feature and `child_agents_md` config schema
entry
- remove the hierarchical prompt asset, export, and instruction
injection
- remove feature-specific tests and documentation
- keep the generic unstable-feature warning coverage using
`apply_patch_streaming_events`
Normal project `AGENTS.md` discovery and composition are unchanged.
## Testing
- `just test -p codex-features`
- `just test -p codex-prompts`
- `just test -p codex-core agents_md`
- `just test -p codex-core unstable_features_warning`
This eliminates redundant user documentation and allows us to focus our
documentation investments.
I left tombstone files for most of the existing ".md" docs files to
avoid broken links. These now contain brief links to the developers docs
site.