Restore legacy image detail values

[rhan-oai]

Why

Older persisted rollouts can contain input_image.detail values of auto or low from before ImageDetail was narrowed to high/original. Current deserialization rejects those values, which can make resume skip later compacted checkpoints and reconstruct an oversized raw suffix before the next compaction attempt.

Confirmed Sentry reports fixed by this compatibility path:

• CODEX-1H3F
• CODEX-1H6N
• CODEX-1JDP
• CODEX-1HW6

Background

openai/codex#20693 added image-detail plumbing for app-server UserInput so input images could explicitly request detail: original. The Slack discussion behind that PR was about ScreenSpot / bridge evals where user input images were resized, while tool output images already had MCP/code-mode ways to request image detail.

In review, the intended new API surface was narrowed to high and original: default to high, allow original when callers need unchanged image handling, and avoid encouraging new auto or low usage. That policy still makes sense for newly emitted values.

The missing compatibility piece is persisted history. Older rollouts can already contain auto and low, and resume reconstructs typed history by deserializing those rollout records. Rejecting old values at that boundary causes valid compacted checkpoints to be skipped. This PR restores auto and low as real variants so old records deserialize and round-trip without being rewritten as high, while product paths can continue to default to high and avoid emitting auto for new behavior.

What changed

• Restored ImageDetail::Auto and ImageDetail::Low as first-class protocol values.
• Preserved auto/low through rollout deserialization, MCP image metadata, code-mode image output, and schema/type generation.
• Kept local image byte handling conservative: only original switches to original-resolution loading; auto/low/high continue through the resize-to-fit path while retaining their detail value.
• Added regression coverage for enum round-tripping and code-mode low detail handling.

Testing

• just write-app-server-schema
• just test -p codex-protocol
• just test -p codex-tools
• just test -p codex-code-mode
• just test -p codex-app-server-protocol
• just test -p codex-core suite::rmcp_client::stdio_image_responses_preserve_original_detail_metadata
• just test -p codex-core suite::code_mode::code_mode_can_use_mcp_image_result_with_image_helper
• Loaded broken rollouts on local fixed builds, and started/completed new turns.

I also attempted just test -p codex-core; the local broad run did not finish green: 2559 tests run, 2467 passed, 55 flaky, 91 failed, 1 timed out. The failures were broad timeout/deadline failures across unrelated areas; targeted changed-path core tests above passed.