fix: extract usage and finish reason from OpenRouter provider metadata

[konard]

Summary

Fixes #187 - Not all data provided about response of kilo/glm-5-free model

When using OpenRouter-compatible APIs (like Kilo Gateway), the standard AI SDK usage object may be empty while the actual usage data is in providerMetadata.openrouter.usage. This PR adds fallback logic to extract token counts and finish reason from provider metadata.

Root Cause

The @openrouter/ai-sdk-provider SDK initializes usage with NaN values and only populates them when streaming chunks contain usage data in the expected format. When the Kilo API sends usage data in a different format or timing, the standard usage remains empty while providerMetadata contains the actual data.

Before fix:

{
  "reason": "unknown",
  "cost": 0,
  "tokens": { "input": 0, "output": 0, "reasoning": 0, "cache": { "read": 0, "write": 0 } }
}

After fix:

{
  "reason": "stop",
  "cost": 0,
  "tokens": { "input": 12004, "output": 103, "reasoning": 86, "cache": { "read": 0, "write": 0 } }
}

Changes

• js/src/session/index.ts: Fall back to openrouter metadata when standard usage is empty (inputTokens/outputTokens undefined)
• js/src/session/processor.ts: Infer finish reason as "stop" when standard finishReason is undefined but openrouter usage is present

Case Study

A detailed case study with root cause analysis is documented in docs/case-studies/issue-187/case-study.md.

Upstream Issue

Reported to the OpenRouter AI SDK provider maintainers: OpenRouterTeam/ai-sdk-provider#419

Testing

Verified manually with kilo/glm-5-free model:

echo 'hi' | agent --model kilo/glm-5-free

Token counts and finish reason are now correctly extracted.

[konard]

🤖 Solution Draft Log

This log file contains the complete execution trace of the AI solution draft process.

💰 Cost estimation:

• Public pricing estimate: $8.867155
• Calculated by Anthropic: $6.546125 USD
• Difference: $-2.321029 (-26.18%)
  📎 Log file uploaded as Gist (1064KB)
  🔗 View complete solution draft log

---

Now working session is ended, feel free to review and add any feedback on the solution draft.