feat: add OpenRouter quantization filter to exclude low-bit providers

[roomote]

Related GitHub Issue

Closes: #11325

Description

This PR attempts to address Issue #11325. Feedback and guidance are welcome.

When using OpenRouter with CJK languages (Korean, Chinese, Japanese), low-bit quantization providers (FP4/FP6/Int4) can produce broken Unicode escape sequences instead of readable text. This adds an opt-in checkbox to filter out those providers.

Implementation details:

1. Schema (packages/types/src/provider-settings.ts): Added openRouterExcludeLowQuantization: z.boolean().optional() to the openRouterSchema.

2. Handler (src/api/providers/openrouter.ts): Extracted provider options logic into a buildProviderOptions() method that combines both specific provider routing and quantization filtering. When the setting is enabled, provider.quantizations is set to ["fp16", "bf16", "fp8", "int8"], restricting to higher-precision providers. This is applied to both createMessage() and completePrompt().

3. UI (webview-ui/src/components/settings/providers/OpenRouter.tsx): Added a checkbox labeled "Exclude low-bit quantization (FP4/FP6/Int4)" with a description explaining the CJK encoding fix.

4. i18n (webview-ui/src/i18n/locales/en/settings.json): Added English translations for the new UI labels.

Test Procedure

• Added 4 new tests in src/api/providers/__tests__/openrouter.spec.ts:
  • Verifies quantizations are included in providerOptions when enabled
  • Verifies quantizations are NOT included when disabled
  • Verifies quantizations combine correctly with specific provider routing
  • Verifies quantizations work in completePrompt() as well
• All 45 tests pass: cd src && npx vitest run api/providers/__tests__/openrouter.spec.ts

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes (if applicable).
• Documentation Impact: No documentation updates are required.
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

• No documentation updates are required.

Additional Notes

The setting defaults to off, preserving existing behavior. When enabled, it uses the OpenRouter documented provider.quantizations API field to restrict routing to higher-precision providers only.

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Important

Adds a feature to filter out low-bit quantization providers in OpenRouter settings, with schema, handler, UI, and i18n updates.

• Behavior:
  • Adds openRouterExcludeLowQuantization to openRouterSchema in provider-settings.ts to filter out low-bit quantization providers.
  • Updates OpenRouterHandler in openrouter.ts to include quantization filtering in buildProviderOptions().
  • Adds a checkbox in OpenRouter.tsx to enable/disable the quantization filter.
• Tests:
  • Adds tests in openrouter.spec.ts to verify quantization filtering behavior when enabled/disabled and its combination with specific provider routing.
• i18n:
  • Adds English translations for new UI labels in settings.json.

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[roomote]

Rooviewer   See task

Reviewed all changed files across both commits. No issues found -- the implementation is clean, well-scoped, and non-breaking. The latest commit correctly adds missing translation keys to all 17 non-English locales.

Previous reviews

• 0bb4567: Review #1

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