Extract the shared pure primitives and the chat->Responses direction out of the
894-line openai-responses.ts request translator:
- openai-responses/helpers.ts: pure primitives (toRecord/toString/clampCallId/
normalizeVerbosity/etc + markers/regexes/JsonRecord), zero host imports
- openai-responses/toResponses.ts: openaiToOpenAIResponsesRequest (chat->Responses),
imports the helpers leaf
Host keeps openaiResponsesToOpenAIRequest (Responses->chat, imported by production)
plus both register() directions, and re-exports openaiToOpenAIResponsesRequest so
external importers (tests) keep working.
Host 894 -> 529 LOC (under the 800 cap). Verbatim bodies (multiset check: leaf A 54/54,
leaf B 294 lines, fn1 intact), public export set unchanged, leaves never import the host
(no cycle). Adds a split-guard test; all consumer tests stay green (responses-translation-fixes
37, verbosity 4, reasoning-effort 4, orphaned-tool-filter 8, empty-tool-name-loop 8,
headroom-responses-format 3).
