## Intent
Keep Bazel and Starlark files consistently formatted without requiring
contributors to install or version buildifier themselves.
## Implementation
- Add a SHA-256-pinned, cross-platform DotSlash manifest for buildifier
v8.5.1.
- Run buildifier from the shared `just fmt` and `just fmt-check` driver,
with Windows-safe explicit DotSlash invocation.
- Provision DotSlash in formatting CI and contributor devcontainers, and
document the source-build prerequisite.
- Apply the initial mechanical buildifier formatting baseline.
## Why
Add a standalone image generation path that can be exercised
independently of hosted Responses image generation, while retaining the
hosted tool as fallback unless the extension is actually available to
the model.
## What changed
- Added the `codex-image-generation-extension` crate with standalone
generate/edit execution, prior-image selection for edits, model-visible
image output, and local generated-image persistence.
- Installed the extension in app-server behind the disabled-by-default
`imagegenext` feature and backend eligibility checks.
- Updated core tool planning so eligible `image_gen.imagegen` exposure
replaces hosted `image_generation`, while unavailable configurations
retain hosted fallback.
- Added coverage for extension behavior, edit history reuse, feature
gating, auth eligibility, and hosted-tool replacement.
- The extension is installed through app-server only in this PR; other
execution paths retain hosted image generation because hosted
replacement occurs only when the standalone executor is actually
registered and model-visible.
- The initial extension contract intentionally fixes the image model to
`gpt-image-2` and uses automatic image parameters.
- Native generated-image history/card parity and rollout persistence
cleanup are intentionally deferred follow-up work.
## Validation
- `just test -p codex-image-generation-extension`
- `just test -p codex-features`
- `just test -p codex-core
hosted_tools_follow_provider_auth_model_and_config_gates`
- `just test -p codex-app-server`
- `just fix -p codex-image-generation-extension -p codex-features -p
codex-core -p codex-app-server`
- `just fmt`
- `just bazel-lock-update`
- `just bazel-lock-check`
---------
Co-authored-by: jif-oai <jif@openai.com>
