Local compaction request omits tool specs, so it never hits the prompt cache (full window re-billed uncached on every compaction)

Version / context

codex-cli 0.146.1 (code references pinned to tag rust-v0.146.1). Affects every provider that takes the local compaction path (all non-OpenAI/Azure providers today; and OpenAI users too if #34428 is fixed by routing custom compact prompts locally).

What happens

run_compact_task_inner_impl builds the summarization request as

https://github.com/openai/codex/blob/rust-v0.146.1/codex-rs/core/src/compact.rs#L277-L281

let prompt = Prompt {
    input: turn_input,
    base_instructions: sess.get_base_instructions().await,
    ..Default::default()
};

i.e. without tools / parallel_tool_calls, while every regular turn in the same session serializes the tool specs into the request (see the remote analogue, which does include them: https://github.com/openai/codex/blob/rust-v0.146.1/codex-rs/core/src/compact_remote_request.rs#L63-L70).

Prompt caching is prefix-based over the serialized request including tools, so the compaction request's prefix never matches the session's cached prefix. Result: the entire conversation history is re-billed uncached on every compaction.

Measured impact

On a long-running session: compaction triggers at ~235k input tokens and normal turns run 96–99% cached. A prefix-mismatched compaction re-bills the full ~235k uncached each time; across a thread with frequent compactions this added roughly +70% to total uncached input on our workload.

Suggested fix (validated locally)

Mirror the remote request builder: include tools: step_context.tool_router.model_visible_specs() and parallel_tool_calls: turn_context.model_info.supports_parallel_tool_calls in the local compaction Prompt. We applied exactly this on top of rust-v0.146.1: compaction requests then hit the prompt cache (65–88% cached even on a small verification session whose uncached tail was dominated by freshly read files), summaries are unaffected, and cargo test -p codex-core --lib compact / --test all compact match pristine (54 / 115 passing).

Interaction

This compounds with #34428: any fix that makes compact_prompt effective by routing to local compaction will surface this cost bug for the default provider as well.

pip install codex-rescue==0.1.0a5
codex-rescue doctor <path-to-rollout.jsonl>