Fixes #5144: Add comprehensive test coverage for OpenRouter upstream_inference_cost

[roomote]

Summary

This PR addresses issue #5144 by adding comprehensive test coverage for OpenRouter's upstream_inference_cost functionality.

Changes

• Added test for BYOK cost calculation using upstream_inference_cost
• Added test for graceful handling of missing upstream_inference_cost
• Added test for reasoning tokens support
• Verified cached token display functionality

Investigation Results

Upon investigation, I found that the OpenRouter implementation was already correctly using upstream_inference_cost in the cost calculation (line 171 in src/api/providers/openrouter.ts):

totalCost: (lastUsage.cost_details?.upstream_inference_cost || 0) + (lastUsage.cost || 0),

The implementation also properly handles cached tokens:

cacheReadTokens: lastUsage.prompt_tokens_details?.cached_tokens,

Testing

All tests pass, confirming the existing implementation correctly:

• Uses upstream_inference_cost for BYOK cost calculation
• Falls back gracefully when upstream_inference_cost is missing
• Displays cached tokens properly
• Supports reasoning tokens

The issue appears to have been resolved in a previous change, and this PR adds the missing test coverage to ensure the functionality is properly validated.

Fixes #5144

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Important

Adds comprehensive test coverage for upstream_inference_cost in OpenRouterHandler, ensuring correct cost calculation and token handling.

• Tests Added:
  • upstream_inference_cost for BYOK cost calculation in openrouter.spec.ts.
  • Graceful handling of missing upstream_inference_cost in openrouter.spec.ts.
  • Support for reasoning tokens in openrouter.spec.ts.
  • Verification of cached token display in openrouter.spec.ts.
• Implementation Verification:
  • Confirmed upstream_inference_cost is used correctly in cost calculation.
  • Confirmed cached tokens are handled properly.
• Misc:
  • All tests pass, confirming correct functionality.

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[delve-auditor]

✅ No security or compliance issues detected. Reviewed everything up to 098ca59.

Security Overview

• 🔎 Scanned files: 1 changed file(s)

Detected Code Changes

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