fix: convert to BigInt before nanosecond multiplication to avoid precision loss

[claygeo]

Summary

Closes #3292

Multiplying epoch milliseconds by 1,000,000 as a Number exceeds Number.MAX_SAFE_INTEGER (~9e15), causing IEEE 754 precision loss of ~256ns in ~0.2% of cases. The fix converts to BigInt first, then multiplies.

Changes

4 locations fixed across 3 files:

File	Function	Line
common.server.ts	getNowInNanoseconds()	24
common.server.ts	calculateDurationFromStart()	38
index.server.ts	recordRunDebugLog()	218
runEngineHandlers.server.ts	retry event recording	431

// Before: multiplication in float-land (exceeds MAX_SAFE_INTEGER)
BigInt(new Date().getTime() * 1_000_000)

// After: multiplication in BigInt-land (exact)
BigInt(new Date().getTime()) * BigInt(1_000_000)

The correct pattern already existed in convertDateToNanoseconds() in the same file — these locations just weren't using it.

Test plan

• All 4 locations use BigInt multiplication instead of Number multiplication
• No behavioral change for correctly-rounded timestamps (~99.8% of cases)
• Eliminates ~256ns errors for the ~0.2% of timestamps that previously lost precision

[changeset-bot]

⚠️ No Changeset found

Latest commit: a125348

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[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 9d942296-0e95-40c4-b200-8729f5641d0a

📥 Commits

Reviewing files that changed from the base of the PR and between cf0fdde and a125348.

📒 Files selected for processing (3)

• apps/webapp/app/v3/eventRepository/common.server.ts
• apps/webapp/app/v3/eventRepository/index.server.ts
• apps/webapp/app/v3/runEngineHandlers.server.ts

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Walkthrough

Three files in the event repository and run engine handlers were updated to standardize nanoseconds conversion arithmetic. The changes reorder arithmetic operations to convert millisecond timestamps to BigInt before multiplication rather than multiplying as numbers first. Specifically, getNowInNanoseconds() and calculateDurationFromStart() in the common module, the startTime calculation in the event repository index, and the retry event handling in the run engine handlers all follow this pattern. No function signatures were altered.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 1 additional finding.