Round 2 reviewer feedback:
- studio/frontend/src/features/chat/types/api.ts: `OpenAIChatCompletionsRequest.service_tier` did not include `"scale"`, so the request builder in chat-adapter.ts failed typecheck after the runtime ServiceTier union widened (`Type 'ServiceTier | undefined' is not assignable...`). Widen the type to match the SDK and keep the typecheck green.
- studio/frontend/src/components/ui/stop-sequences-input.tsx: the chip editor used `draft.trim()` for storage, which silently mutated semantically meaningful stops like " End", "### ", and "\n\n". Keep the whitespace-only rejection (Anthropic 400s on those, OpenAI silently drops them) but persist the raw draft so leading/trailing whitespace inside otherwise-meaningful stops survives.
- studio/backend/core/inference/external_provider.py: the Kimi web-search bypass dropped a single string `stop="\n\n"` via `stop.strip()` while the normal default OAI-compat path forwards it verbatim. Mirror the default path's behavior here so kimi-with-search and kimi-without-search apply the same rules (asymmetric provider-path fix flagged in round-2 review).
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