OpenCode pins requests sharing an x-opencode-session value to one upstream
backend, which is what keeps its prompt cache warm across a conversation.
Hermes never sent it, so cache ratios on OpenCode traffic were poor.
- agent/opencode_affinity.py: single owner of the header — target detection
(built-in zen/go/free, custom opencode-* providers, any opencode.ai URL)
and the key (affinity scope → conversation root → session id, cron
timestamp stripped), same resolution as OpenRouter/xAI affinity hints.
- build_api_kwargs: merged once after the per-mode builder, so
chat_completions, codex_responses and anthropic_messages all carry it.
- auxiliary _build_call_kwargs: same key from the runtime-main session so
compression/title/vision calls stay on the conversation's backend; the
aux Codex and Anthropic adapters now forward extra_headers.
Closes#81584, #81832 (deepseek-v4-flash 400 without the header).
Teknium
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