Adds the missing sampling parameters that the upstream APIs accept and
that Studio's chat UI previously hid. Each knob is gated per provider
so the picker never offers a field the upstream would 400 on, and the
per-provider stream functions translate / drop fields to match each
API's naming.
New `InferenceParams` fields (round-trip through PersistedInferenceParams
and the chat-settings server store automatically):
- frequencyPenalty (-2..2): OpenAI Chat Completions only.
- seed (int | null): OpenAI Chat + OpenAI-compat local backends.
- stop (string[]): all OpenAI Chat + Anthropic Messages. Backend
truncates to 4 entries on OpenAI Chat per docs and renames to
`stop_sequences` on Anthropic.
- serviceTier (auto|default|flex|priority|scale|standard_only):
per-provider enum sets resolved by getServiceTierOptions.
- parallelToolCalls (bool, default true): forwarded as
`parallel_tool_calls` on both OpenAI APIs and inverted into
`disable_parallel_tool_use` on Anthropic.
OpenAI Responses (gpt-5.x / o3) explicitly drops frequencyPenalty /
seed / stop alongside the existing temperature / top_p drop, since
the upstream 400s on all of them. service_tier on Responses accepts a
subset (no `scale`) which the dispatch already enforces.
UI rows land in the existing Sampling section of the chat settings
sheet using ParamSlider (frequency penalty), a numeric Input (seed),
a new chips editor `StopSequencesInput` (stop), Select (service tier),
and Switch (parallel tool calls). Each row's visibility follows the
new ProviderCapabilities flag.
Tests pin the gating contract: stop_sequences renamed on Anthropic,
4-entry truncation on OpenAI Chat, every Responses-rejected field
dropped, schema-level validation for the service_tier Literal and
frequency_penalty range.
Plan: plans/hashed-riding-porcupine.md
91d04741ff