## Why
The prompt image cache was bounded to 32 entries, but not by the size of
those entries. A set of large encoded images could therefore retain
substantially more memory than intended. Cache hits also cloned the full
encoded payload.
## What changed
- cap the cache at 64 MiB of encoded image data while preserving its
existing 32-entry limit
- skip caching an image that exceeds the entire byte budget
- evict least-recently-used entries until the cache is back within its
byte budget
- share cached encoded bytes with `Arc<[u8]>` so cache hits do not
deep-clone image payloads
## Validation
- `just test -p codex-utils-image`
## Summary
- Preserve ICC profiles and EXIF metadata when resizing and re-encoding
prompt images.
- Retain EXIF orientation metadata without rotating or otherwise
modifying the pixel data locally.
- Support metadata preservation for PNG, JPEG, and WebP outputs.
- Continue returning the original bytes when an image does not require
re-encoding.
This intentionally preserves the metadata most important for rendering
prompt images faithfully. Other format-specific metadata is not copied.
## Motivation
Client-side resizing previously discarded image metadata during
re-encoding. This could lose color-profile information and EXIF
orientation needed by downstream image consumers.
#### [git stack](https://github.com/magus/git-stack-cli)
- ✅ `1` https://github.com/openai/codex/pull/27245
- ✅ `2` https://github.com/openai/codex/pull/27247
- ✅ `3` https://github.com/openai/codex/pull/27246
- 👉 `4` https://github.com/openai/codex/pull/27266
## Summary
Adds complete client-side image preparation behind the default-off
`resize_all_images` feature flag.
When enabled, local image producers defer decoding and resizing. Images
are prepared centrally before insertion into conversation history,
covering user input, `view_image`, and structured tool-output images.
## Behavior
- Processes base64 `data:` images in messages and function/custom tool
outputs.
- Leaves non-data URLs, including HTTP(S) URLs, unchanged.
- Applies image-detail budgets:
- `high` and omitted: 2048px maximum dimension and 2.5K 32px patches.
- `original`: 6000px maximum dimension and 10K 32px patches.
- `auto`: uses the same 2048px / 2.5K-patch budget as high.
- `low`: unsupported and replaced with an actionable placeholder.
- Preserves original image bytes when no resize or format conversion is
needed.
- Enforces the shared 1 GiB encoded and decoded data-URL sanity limits.
- Replaces only an image that fails preparation, preserving sibling
content and tool-output metadata.
- Uses bounded placeholders distinguishing generic processing failures,
oversized images, and unsupported `low` detail.
- Prepares resumed and forked history before installing it as live
history without modifying persisted rollouts.
## Flag-Off Behavior
When `resize_all_images` is disabled:
- Existing local user-input and `view_image` processing remains
unchanged.
- Existing decoding and error behavior remains unchanged.
- Arbitrary tool-output images are not processed.
- HTTP(S) image URLs continue to be forwarded unchanged.
#### [git stack](https://github.com/magus/git-stack-cli)
- ✅ `1` https://github.com/openai/codex/pull/27245
- 👉 `2` https://github.com/openai/codex/pull/27247
- ⏳ `3` https://github.com/openai/codex/pull/27246
- ⏳ `4` https://github.com/openai/codex/pull/27266
## Summary
Add shared image-processing primitives needed for centralized image
preparation in a follow-up PR.
- Add `load_data_url_for_prompt` for decoding and preparing base64 image
data URLs.
- Add configurable maximum-dimension and 32px patch-budget resizing.
- Enforce a 1 GiB sanity limit on both encoded and decoded data-URL
representations.
- Preserve original PNG, JPEG, and WebP bytes when resizing is
unnecessary.
- Preserve the existing GIF-to-PNG behavior.
- Move image utility tests into the existing sidecar test module.
## Behavior
This PR is intended to be runtime behavior-preserving.
Existing production callers continue using
`PromptImageMode::ResizeToFit` and `PromptImageMode::Original` with
their existing semantics. The new data-URL entrypoint and configurable
resize mode have no production callers in this PR; they are used by the
next PR in the stack.
This PR does not change user-input handling, `view_image`, history
insertion, request construction, HTTP image URL forwarding, or
app-server behavior.
#### [git stack](https://github.com/magus/git-stack-cli)
- 👉 `1` https://github.com/openai/codex/pull/27245
- ⏳ `2` https://github.com/openai/codex/pull/27247
- ⏳ `3` https://github.com/openai/codex/pull/27246
- ⏳ `4` https://github.com/openai/codex/pull/27266
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