refactor(backend): extract shared usdcToStroops helper to eliminate float rounding drift

[leocagli]

Fixes #13

Problem

BigInt(Math.round(parseFloat(amount) * 10_000_000)) was duplicated across four call sites in services.js and agents.js. Floating-point multiplication gives incorrect results for some USDC amounts: parseFloat("0.0000001") * 10_000_000 yields 0.9999999... which rounds to 0 instead of 1 stroop.

Solution

New file backend/src/lib/stroops.js with integer-only arithmetic:

export function usdcToStroops(usdc) {
  // Splits on '.', pads/truncates fractional part to 7 digits,
  // then assembles with BigInt arithmetic — no floating-point involved.
  const [intPart, rawFrac = ''] = str.split('.');
  const frac = rawFrac.slice(0, 7).padEnd(7, '0');
  return BigInt(intPart) * 10_000_000n + BigInt(frac);
}

export function stroopsToUsdc(stroops) { ... }

Replaced all four inline conversions:

• services.js → weatherPrice and searchPrice calls to recordPaymentOnChain
• agents.js → can-spend route and payment record route

🤖 Generated with Claude Code

[coderabbitai]

Warning

Review limit reached

@leocagli, we couldn't start this review because you've reached your PR review rate limit.

More reviews will be available in 1 second. Learn how PR review limits work.

To continue reviewing without waiting, enable usage-based billing in the billing tab.

⌛ How to resolve this issue?

After more reviews become available, a review can be triggered using the @coderabbitai review command as a PR comment. Alternatively, push new commits to this PR.

To avoid repeated limits, reduce automatic review volume by pausing incremental auto-reviews earlier, using label-based review opt-in, excluding WIP or generated PR titles, or requesting reviews manually when the PR is ready. If your team needs uninterrupted high-volume reviews, an organization admin can enable usage-based credits.

🚦 How do rate limits work?

CodeRabbit enforces per-developer PR review limits for each organization. Most developers receive the normal plan refill rate.

For paid Pro and Pro+ PR reviews, CodeRabbit uses adaptive limits for sustained high-volume activity. When a developer's recent PR review activity reaches the 95th percentile or higher among CodeRabbit users, the refill rate gradually slows as usage increases. The highest same-day bursts are limited more strictly.

Please see our Fair Usage Limits Policy for further information.

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 8e792346-675f-46e5-871d-ee03d2ebe1fd

📥 Commits

Reviewing files that changed from the base of the PR and between 6fb6da9 and 5a6948d.

📒 Files selected for processing (3)

• backend/src/lib/stroops.js
• backend/src/routes/agents.js
• backend/src/routes/services.js

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}