[LukasParke]

Description

Fixes #587

Bug. In the chat model, providerOptions.openrouter.provider replaced the configured provider routing instead of merging into it. doGenerate/doStream built the body as { ...this.getArgs(options), ...restOpenrouterOptions }. Here getArgs() sets provider: this.settings.provider (and then spreads both extraBodys), so a runtime provider object overrode all of it. The completion model had the same pattern for extraBody.provider. Completion has no typed provider setting.

Repro.

const model = openrouter.chat('google/gemini-2.5-flash', {
  provider: { order: ['google'], allow_fallbacks: false, sort: 'price' },
});
await generateText({ model, prompt: 'hi', providerOptions: { openrouter: { provider: { order: ['anthropic'] } } } });
// sent provider: { order: ['anthropic'] } (allow_fallbacks and sort are lost)

Fix. Same semantics as the image model (#551): a shallow merge with precedence settings.provider < config.extraBody.provider < settings.extraBody.provider < providerOptions.openrouter.provider. Non-object values (null, arrays, primitives) are ignored.

• New helper src/utils/merge-provider-routing.ts (mergeProviderRouting). The image model keeps its own inline merge (same semantics), see Merge coordination below.
• Chat: doGenerate and doStream.
• Completion: doGenerate and doStream, using the two extraBody sources plus runtime.

Behavior change (noted in the changeset): a runtime provider object no longer drops configured keys it doesn't set. To override a key, set it explicitly in the runtime object.

Not changed. Embedding, reranking and evaluation spread providerOptions.openrouter differently, and the issue doesn't cover them. I left them alone to keep this PR scoped. I can follow up if we want the same semantics there.

Tests.

• src/chat/index.test.ts: the issue's example in doGenerate and doStream, full precedence across all four sources, and a null runtime provider being ignored.
• src/completion/index.test.ts: provider and model extraBody merged with runtime, in doGenerate and doStream.
• src/utils/merge-provider-routing.test.ts: unit tests for the helper.
• e2e/issues/issue-587-provider-routing-merge.test.ts: issue regression test (pnpm test:issues, mocked fetch). It runs the issue's example through generateText.

I checked that the 6 new chat/completion tests and the issue test fail on origin/main and pass with this fix.

Checklist

• I have run pnpm stylecheck and pnpm typecheck
• I have run pnpm test and all tests pass
• I have added tests for my changes (if applicable)
• I have updated documentation (if applicable)

Changeset

• I have run pnpm changeset to create a changeset file

Merge coordination

Merges cleanly with #603 and #597 in either order, so no hand resolution is needed. The image model is no longer refactored onto mergeProviderRouting. Its new import landed on the same line as #603's user-agent import, and the refactor didn't change behaviour, so src/image/index.ts stays as on main. I checked this with local integration merges of #590–#609 in both orders.

🤖 Generated with Claude Code

[LukasParke]

Closing as superseded by #628 (merged), which merges provider routing in the chat and completion models through the shared mergeProviderRouting helper and closed #587.