## Why
Remote compaction v2 is ready to become the default for providers that
already support remote compaction. Leaving it behind an
under-development opt-in keeps eligible sessions on the legacy
remote-compaction path.
This does not broaden provider eligibility: OpenAI and Azure move to v2,
while Bedrock and OSS providers retain their existing local-compaction
behavior.
## What changed
- Mark `remote_compaction_v2` stable and enable it by default.
- Make tests that intentionally cover legacy remote compaction
explicitly disable v2.
- Update parity coverage so v2 exercises the production default and only
legacy mode opts out.
## Verification
- `just test -p codex-core
auto_compact_runs_after_resume_when_token_usage_is_over_limit
auto_compact_counts_encrypted_reasoning_before_last_user
auto_compact_runs_when_reasoning_header_clears_between_turns
responses_lite_compact_request_uses_lite_transport_contract`
## Summary
- Strip image `detail` fields from every Responses Lite request.
- Apply stripping to message images and function/custom tool-output
images.
- Transform only the formatted request copy without mutating stored
history.
- Preserve image URLs byte-for-byte, including HTTP(S) URLs, without
downloading, validating, or resizing them.
- Preserve all image `detail` fields for non-Responses-Lite models.
## Motivation
Responses Lite does not support image `detail` tags, so Codex must omit
them whenever `model_info.use_responses_lite` is enabled. This transport
requirement is independent of the `resize_all_images` feature.
Stored history retains the original detail values. This keeps
request-specific formatting isolated from conversation state and
preserves the information for local image preparation and
non-Responses-Lite requests.
#### [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
- send `X-OpenAI-Internal-Codex-Responses-Lite: true` on HTTP Responses
requests and WebSocket upgrade requests when model metadata enables
Responses Lite
- use client metadata when sending it over the websocket
This PR is stacked on #26490.
## Why
The Responses Lite marker is request-scoped for HTTP but
connection-scoped for Responses-over-WebSocket because it is carried on
the upgrade request. Reusing a cached socket opened for the opposite
mode would therefore send the wrong transport contract.
## Validation
- `just test -p codex-core responses_lite`
- `just test -p codex-core
responses_websocket_reconnects_when_responses_lite_mode_changes`
- `just fix -p codex-core`
- `just fmt`
## Summary
Responses Lite does not execute hosted Responses tools, so models using
it must route web search and image generation through Codex-owned
executors & standalone Response's API endpoints.
This PR is stacked on #26487.
## Validation
- `cargo test -p codex-core responses_lite_ --lib`
- `cargo test -p codex-core
standalone_executors_remain_hidden_without_flags_or_responses_lite
--lib`
- `cargo test -p codex-core
hosted_tools_follow_provider_auth_model_and_config_gates --lib`
- `cargo test -p codex-web-search-extension -p
codex-image-generation-extension`
- `cargo test -p codex-app-server --test all standalone_`
- `cargo fmt --all -- --check`
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Curtis 'Fjord' HawthorneandGitHub
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