fix: remove artificial BigInt overflow guard in liquidation PnL (H7)

[0x-SquidSol]

Summary

• The overflow check clamped PnL at Number.MAX_SAFE_INTEGER (9e15), which is meaningless for BigInt (arbitrary precision)
• Large positions where diff * positionSize > 9e15 were clamped to a positive value
• This could make deeply underwater accounts appear healthy, preventing valid liquidations
• The re-verification path (line 435) never had this guard and worked correctly

Fix

Remove the MAX_SAFE_BIGINT overflow guard. BigInt arithmetic in JavaScript has arbitrary precision — no overflow is possible. The PnL calculation now matches the re-verification path.

Test plan

• All 133 tests pass

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed large position liquidation PnL calculations by removing unnecessary overflow safeguards that were incorrectly clamping profit/loss values for substantial trading positions, ensuring accurate calculations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 512b59a9-a629-48c0-8804-a8fa024770c8

📥 Commits

Reviewing files that changed from the base of the PR and between 4fd5e86 and ddb178a.

📒 Files selected for processing (1)

• src/services/liquidation.ts

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📝 Walkthrough

Walkthrough

The liquidation service was simplified by removing BigInt overflow protection logic that compared position sizes against a MAX_SAFE_BIGINT threshold, replacing it with a straightforward PnL calculation that always computes markPnl as (diff * absPosSize) / price when prices are positive.

Changes

Cohort / File(s)	Summary
PnL Calculation Simplification src/services/liquidation.ts	Removed overflow "protection" conditional branches that clamped markPnl to ±MAX_SAFE_BIGINT. Simplified PnL computation to a single path: (diff * absPosSize) / price when entryPrice > 0n && price > 0n.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 Away with overflow fears, the code now flows so clean,
One path instead of branching paths, the simplest ever seen,
BigInt calculations dance without the guards of old,
Liquidation logic lighter now—a tale efficiently told! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically summarizes the main change: removing an artificial BigInt overflow guard in liquidation PnL calculation, with reference to the issue (H7).
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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