src/lib/providers.ts holds a per-provider spec (url, headers, body,
extractor, default model) and a single callProvider() covering both the
action-prompt and custom-prompt families (~250 lines -> one path).
getSystemPrompt, fetchWithTimeout, and listModels move along with it;
background.ts drops from 553 to 130 lines.
Behavior pinned by 20 parity tests written from the old functions
(request shapes, headers, defaults, error strings). One deliberate
change: max_tokens now scales with input length (1024-8192) instead of
a hard-coded 1024, so Expand no longer truncates long selections.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
