Add under-development original-resolution view_image support

[fjord-oai]

Summary

Add original-resolution support for view_image behind the under-development view_image_original_resolution feature flag.

When the flag is enabled and the target model is gpt-5.3-codex or newer, view_image now preserves original PNG/JPEG/WebP bytes and sends detail: "original" to the Responses API instead of using the legacy resize/compress path.

What changed

• Added view_image_original_resolution as an under-development feature flag.
• Added ImageDetail to the protocol models and support for serializing detail: "original" on tool-returned images.
• Added PromptImageMode::Original to codex-utils-image.
  • Preserves original PNG/JPEG/WebP bytes.
  • Keeps legacy behavior for the resize path.
• Updated view_image to:
  • use the shared local_image_content_items_with_label_number(...) helper in both code paths
  • select original-resolution mode only when:
    • the feature flag is enabled, and
    • the model slug parses as gpt-5.3-codex or newer
• Kept local user image attachments on the existing resize path; this change is specific to view_image.
• Updated history/image accounting so only detail: "original" images use the docs-based GPT-5 image cost calculation; legacy images still use the old fixed estimate.
• Added JS REPL guidance, gated on the same feature flag, to prefer JPEG at 85% quality unless lossless is required, while still allowing other formats when explicitly requested.
• Updated tests and helper code that construct FunctionCallOutputContentItem::InputImage to carry the new detail field.

Behavior

Feature off

• view_image keeps the existing resize/re-encode behavior.
• History estimation keeps the existing fixed-cost heuristic.

Feature on + gpt-5.3-codex+

• view_image sends original-resolution images with detail: "original".
• PNG/JPEG/WebP source bytes are preserved when possible.
• History estimation uses the GPT-5 docs-based image-cost calculation for those detail: "original" images.

git stack

• 👉 1 Add under-development original-resolution view_image support #13050
• ⏳ 2 Enforce the Responses API 50 MB image limit #13049