Add SiliconFlow as a built-in provider

[Rex-Gao]

What

Adds SiliconFlow (硅基流动) as a sixth provider alongside TypeSafe, OpenRouter, Cloudflare, Vercel, and the generic compatible endpoint:

• SILICONFLOW_API_KEY auto-selects SiliconFlow when it is the only configured provider credential, outranking the compatible fallback; JEV_PROVIDER=siliconflow forces it.
• The transport POSTs the standard { model, state, questions } contract to https://api.siliconflow.cn/v1/systemone and reuses the local fetch-based resilience path: the 408/409/429/5xx retry allowlist, the 1 MB streamed byte ceiling, the whole-request deadline, and fixed-string client-visible errors.
• The default jev-latest maps to SiliconFlow's current alias semif, mirroring the OpenRouter jev-1.13 mapping. Unknown model names are sent verbatim for the endpoint to reject — no silent rewriting, per the "configuration errors, never silent fallbacks" rule.
• The API root is overridable via JEV_SILICONFLOW_BASE_URL, following the existing JEV_OPENROUTER_BASE_URL / JEV_CLOUDFLARE_BASE_URL convention (this is also what makes the transport testable against a local mock).

Why

SiliconFlow is a practical carrier for callers who cannot reach TypeSafe or OpenRouter reliably. The endpoint speaks the same System One contract the compatible adapter already targets, so this is a small, self-contained transport with no new dependencies.

Testing

• npm run typecheck, npm run build, and npm test pass: 246 tests, including 7 new ones covering the wire request shape and auth header, the jev-latest → semif alias mapping, auto-selection (alone and in preference over a complete compatible credential pair), non-2xx statuses surfacing as fixed-string errors without upstream body text, malformed 200 bodies, and the missing-key configuration error.

Notes for review

• Auto-detection order: the dedicated provider key outranks the generic compatible fallback when both are configured (TypeSafe/OpenRouter/Cloudflare/Vercel credentials still win over both, exactly as before).
• The branch is based on current main (0.10.1) and follows the fixed-string error convention from 0.10.0 — no upstream response text reaches MCP-visible errors.

[jkudish]

Thank you for submitting this. The transport is well built and the tests are thorough.

Provider and transport support now live in @jkudish/jev-agent-tools, the shared transport layer for Jev, so new carriers are added there rather than in jev-mcp. The adding a provider guide covers the options, including publishing yours as a third-party driver package.

If you publish one, a PR linking it from the READMEs is welcome.

[Rex-Gao]

Thanks for the pointer! The transport now lives where it belongs: jkudish/jev-agent-tools#4 adds SiliconFlow as a built-in driver there, following the add-a-provider guide (driver shape, fixed-string errors, jev-latest → semif mapping, hermetic tests).

Happy to close this in favor of that PR — and if you'd like, the README link from jev-mcp's provider section can land separately once it's released.