Function overwriteCostWithBilledCredits

web/src/llm-api/openrouter.ts:1085–1108

* Overwrite the cost field in the final SSE chunk to reflect actual billed credits. * This ensures the SDK calculates the exact credits value we stored in the database, * making the server the single source of truth for credit tracking.

(line: string, billedCredits: number)

 * making the server the single source of truth for credit tracking.
 */
function overwriteCostWithBilledCredits(line: string, billedCredits: number): string {
  if (!line.startsWith('data: ')) {
    return line
  }

  const raw = line.slice('data: '.length)
  if (raw === '[DONE]\n' || raw === '[DONE]') {
    return line
  }

  try {
    const obj = JSON.parse(raw)
    // Only modify if there's usage data (final chunk)
    if (obj.usage) {
      obj.usage.cost = creditsToFakeCost(billedCredits)
      obj.usage.cost_details = { upstream_inference_cost: 0 }
      return `data: ${JSON.stringify(obj)}\n`
    }
  } catch {
    // If parsing fails, return original line
  }

  return line
}