docs(openrouter): document provider routing, variants, plugins and reasoning options

[changbaebang]

🎯 Changes

@tanstack/ai-openrouter already forwards OpenRouter's routing surface through modelOptions — provider preferences, variant, plugins, reasoning, and user / sessionId / metadata (see the adapter's header comment in adapters/text.ts and the forwards common options (provider, plugins, etc.) to the SDK request test) — but docs/adapters/openrouter.md only documented the models fallback list and sampling options.

This expands Model Routing with one subsection per option:

• Provider preferences — order / allowFallbacks example, plus only, ignore, requireParameters (and what happens without it: unsupported parameters are dropped silently rather than rejected), sort, maxPrice, quantizations, dataCollection, zdr
• Model variants — variant and its accepted values; notes that it only builds the :variant suffix and is never sent in the body
• Plugins — plugins with the web example and the plugin ids the SDK knows; cross-links to Provider Tools for the tool-shaped alternative
• Reasoning — reasoning.effort values and the enabled: false → effort: "none" normalization the adapter performs
• Session and metadata — sessionId as the sticky routing key

Field names, literal values and descriptions come from @openrouter/sdk (ProviderPreferences, ChatRequestEffort, ProviderSort, Quantization) and the adapter's option types; provider slugs use the SDK's ProviderName casing. docs/config.json updatedAt bumped since this adds sections.

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested code changes locally with pnpm run test:pr, or these tests do not apply to this pull request. (test:docs link verification passes)
• I fully understand the code in this pull request, including any code generated with AI assistance.
• Docs: I updated docs/ for this change, or this change is not user-facing.
• Changeset: I added a changeset (pnpm changeset), or this PR does not change a published package.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).

Summary by CodeRabbit

• Documentation
  • Added OpenRouter model routing guidance, including ordered fallbacks when a preferred model is unavailable.
  • Documented provider preferences, model variants, request plugins, reasoning controls, session identifiers, sticky routing, and metadata.
  • Clarified routing options for fallback behavior, pricing limits, data collection, quantization, and parameter requirements.
  • Documented supported reasoning effort levels and plugin configuration details, including web fetching through the server tool.
  • Updated the OpenRouter adapter documentation date.

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📝 Walkthrough

Walkthrough

The OpenRouter adapter documentation adds model fallback, provider settings, variants, plugins, reasoning, and session metadata details. The navigation entry date changes to 2026-09-18.

Changes

OpenRouter routing documentation

Layer / File(s)	Summary
Document model routing options docs/adapters/openrouter.md, docs/config.json	The documentation describes fallback models, provider routing settings, model variants, request-level plugins, reasoning effort, forwarded session metadata, and the updated navigation date.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to d7a6e

The documentation update has no identified merge-blocking risk.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main documentation changes for OpenRouter provider routing, variants, plugins, and reasoning options.
Description check	✅ Passed	The description includes the required Changes, Checklist, and Release Impact sections. It explains the documentation scope, testing status, checklist completion, and confirms that no published code ch…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 5

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
In `@docs/adapters/openrouter.md`:
- Line 311: Update the provider options documentation entry to describe
dataCollection only with the "deny" value, and add a separate zdr boolean option
documented as zdr: true. Remove wording that presents "zdr" as a dataCollection
value so users construct a valid modelOptions.provider object.
- Line 297: Update the provider.order example to use OpenRouter provider slugs,
changing the display names Groq and Together to lowercase groq and together
while preserving their ordering.
- Line 309: Update the maxPrice documentation entry to describe only the
supported prompt and completion USD-per-million-token limits, removing the
reference to per-modality limits.
- Line 343: Update the OpenRouter documentation to remove `web-fetch` from the
request plugin identifiers and document web fetching through the
`openrouter:web_fetch` server-tool configuration instead. Keep the remaining
supported plugin identifiers and the existing Provider Tools reference intact.
- Line 308: Update the `sort` option documentation to include its supported
object form with `by` and `partition`, while retaining the existing string
values and behavior description.

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[github-actions]

Thanks for the PR, @changbaebang! 🙌 @jherr will take a look.

Automated pre-review checks

• ✅ CI passing
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• ✅ Changeset present
• ✅ E2E test changes included

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