- add /v1/responses (and /responses): OpenAI Responses API support
- streaming semantic events, non-streaming aggregation, function tools
- input item / content / tool / tool_choice conversion to chat format
- ensure first message is system: fix upstream 11128
"first message is not system prompt" for non-harness clients
(assistant/tool-leading or missing system); normalize developer role
- fix tool call delta merging (applyToolCallDelta) across streamed chunks
- refactor handleChatCompletions: extract upstreamChat for 429 cooldown
fallback across the account pool
- bump version to 1.8.1
- tests: 37 passing (session normalization, responses conversion,
tool call merge, responses<->chat mapping)
