Problem

Prompt caching does not work when using codex_responses API mode with OpenAI-compatible providers (e.g. theclawbay). Every request is a cache miss despite prompt_cache_key being set in the request body.

Root cause

Two issues:

1. Missing session routing headers (run_agent.py)

The OpenAI client is initialized without session_id or x-client-request-id headers for codex providers. These headers are required for server-side cache routing — they tell the backend to route requests to the same server that holds the cached prompt prefix.

The official Codex CLI sends these unconditionally. Hermes sets default_headers for OpenRouter, GitHub Copilot, Kimi, and Qwen — but never for Codex/theclawbay.

2. Wrong field name for cache_write_tokens (agent/usage_pricing.py)

The codex_responses branch reads cache_creation_tokens (Anthropic naming convention) instead of cache_write_tokens (OpenAI Responses API naming). This means cache write tokens are always reported as 0.

Fix

Patch 1: Session routing headers

After session_id is assigned during __init__, inject session_id and x-client-request-id into default_headers for codex_responses mode. Also applied in _apply_client_headers_for_base_url() so headers survive /model switches.

Patch 2: cache_write_tokens field

Read cache_write_tokens first (OpenAI naming), fall back to cache_creation_tokens for backward compatibility.

Tests

• test_codex_responses_reads_cache_write_tokens_field — verifies correct field is read
• test_codex_responses_falls_back_to_cache_creation_tokens — backward compat
• test_codex_responses_injects_session_routing_headers — verifies headers are set

Affected files