## Why
Some extension hosts need generated images returned without writing them
to the local filesystem or giving the model a local path.
## What changed
**tl;dr**: we now conduct all extension operations in the image gen
extension
- Let hosts provide an optional image save root when installing the
extension.
- Save images and return path hints only when a save root is configured.
- Return image data without saving or adding a path hint when no save
root is configured.
- Preserve the extension-provided `saved_path` instead of persisting
extension images again in core.
- Leave built-in image generation unchanged.
## Validation
- `just test -p codex-image-generation-extension`
- `just test -p codex-app-server
standalone_image_generation_returns_saved_path_hint_to_model`
- `just test -p codex-core
extension_tool_uses_granted_turn_permissions_without_local_persistence`
- `just test -p codex-core tools::handlers::extension_tools::tests`
- tested on CODEX CLI on both save_root: CODEX_HOME and None
- tested on CODEX APP on both as well
Won ParkandGitHub
61f5a84930