refactor(usage): extract shared OpenRouter/Vercel cost and stream drain helpers

[kilo-code-bot]

Summary

• Extracted three duplicated code patterns across processUsage.ts, processUsage.messages.ts, and processUsage.responses.ts into a new processUsage.shared.ts module:
  • computeOpenRouterCostFields — the OpenRouter BYOK cost computation + suspicious-accounting Sentry warning, previously copy-pasted verbatim in all three files
  • computeVercelCostMicrodollars — the Vercel gateway marketCost/cost parsing, duplicated in messages and responses handlers
  • drainSseStream — the ReadableStream drain loop with ResponseAborted handling, duplicated in all three stream parsers
• No behaviour changes; all three callers pass the same source tag string as before so Sentry tags are preserved.

Verification

• tsgo --noEmit passes with exit code 0
• Tests in src/lib/processUsage*.test.ts could not be run (DB connection unavailable in this environment); the failures are pre-existing infrastructure issues unrelated to this change

Visual Changes

N/A

Reviewer Notes

The only subtle change is that computeOpenRouterCostFields accepts a partial OpenRouterCostFields type (the common cost fields) rather than the full usage object, so callers in messages/responses pass their respective usage types directly — both satisfy the structural type since they have the same cost, is_byok, and cost_details fields.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 file)

• src/lib/processUsage.shared.ts

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_{Reviewed by gpt-5.4-20260305 · 89,781 tokens}

[chrarnoldus-bot]

Clean refactor — three duplicated patterns extracted into well-typed shared helpers with no behavior changes. A few observations:

1. Lost inline comments: The original processOpenRouterUsage in processUsage.ts had useful inline comments explaining why the suspicious-accounting conditions exist (unknown byok status but known non-zero costs, and the BYOK promo note). These are now gone in computeOpenRouterCostFields. Consider adding a brief JSDoc or inline comment in the shared function so future readers don't have to git-blame to understand the rationale.

2. Null safety looks correct: usage ?? {} in processOpenRouterUsage properly handles the nullable input, and the structural typing for OpenRouterCostFields works since all fields are optional.

3. drainSseStream is a nice abstraction — the callback-based onTextChunk pattern keeps it generic while preserving the abort-handling semantics.

All CI green. LGTM.

[chrarnoldus-bot]

Suggestion to re-add the lost inline comments from the original processOpenRouterUsage: