feat(provider): add Synthorai

[cuihuan]

Disclosure: I am affiliated with Synthorai — this adds our own product, not demand I am relaying from elsewhere. Flagging it so the change is judged with that on the table. No expectation of priority, and "not now" is a fine answer.

Prepared with an AI agent. Every value below came from a command I ran; where something was copied rather than checked, that is said outright.

Supersedes my issue #3872, which asked rather than implemented.

What this adds

Synthorai as a provider, following docs/adding-new-provider.md:

File
src/shared/providers/definitions/models/synthorai.ts	model class, extends OpenAICompatible
src/shared/providers/definitions/synthorai.ts	provider definition
src/shared/types/provider.ts	one ModelProviderEnum entry
src/shared/providers/index.ts	one side-effect import

Where I followed the code rather than the guide

The guide is slightly behind definitions/, and I went with the checked-in files. Flagging it in case the doc is meant to be the contract:

• The field table omits modelsDevProviderId and curatedModelIds; 16 of 24 definitions carry the first and the contract test validates the second.
• The guide's createModel reads config.providerSetting.apiKey; the checked-in providers read config.effectiveApiKey.
• Model entries carry maxOutput and nickname, neither of which appears in the guide's example.

Happy to send a docs patch for those separately if useful.

modelsDevProviderId is omitted deliberately

Synthorai has no models.dev entry yet, so naming one would point at nothing and index.contract.test.ts validates that mapping. Eight definitions omit the field, including vercel-ai-gateway, so this follows existing practice rather than skipping something.

The model numbers are reproducible

Every contextWindow, maxOutput and capability came from https://synthorai.io/api/models, which is public and needs no key:

• vision where input_modalities contains image
• tool_use where capabilities contains tools
• reasoning likewise

curl -s https://synthorai.io/api/models | python3 -c "
import json,sys
for r in json.load(sys.stdin)['data']:
    if r['alias'] == 'claude-opus-5':
        print(r['max_input_tokens'], r['max_output_tokens'], r['capabilities'])
"

Seven models are listed, and curatedModelIds names the same seven so the contract test's backing requirement holds.

One honest caveat. For gemini-3.7-flash I initially copied the two numbers from the vercel-ai-gateway entry instead of reading them from the catalog. They happen to match, and I checked afterwards — but the process was wrong, so I would rather you know that one pair was verified late than imply all seven were verified the same way.

No icon

ProviderIcon.tsx takes a 24-grid SVG path and we do not publish a simplified mark at that size. The guide lists the icon as optional, so this omits it rather than shipping something that would look wrong next to the others. Happy to add one if you would prefer a placeholder.

Checks

vitest run src/shared/providers/ — the three contract tests plus the registry suite. Run under Node 22 as engines.node requires; my default is 26 and pnpm correctly refuses it, so I switched rather than passing --engine-strict=false, since a green result from a bypassed engine check would not mean anything.

Where to look

The seven curated models. That is a judgement call about which subset is useful by default rather than something I can verify, and I would rather have your view than guess — the full list is at https://synthorai.io/models/.

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