#747 evaluateBalanceAlerts does not handle negative balances or NaN edge cases

[jotel-dev]

Summary

Fixes #747

Adds validation guards and logging for null, NaN, non-finite, and negative balance values and rule thresholds in evaluateBalanceAlerts.

How Invalid Values Are Handled (Skipped vs Logged vs Error)

1. Logged:
   • Every detected invalid value (e.g. NaN, negative balance numbers < 0, non-finite numbers like Infinity, and malformed rule thresholds) emits a descriptive warning using console.warn that identifies the asset code, rule ID, and the invalid value.
2. Skipped:
   • Invalid comparisons are skipped (continue) rather than proceeding with direct arithmetic. This prevents false alerts (such as a negative balance -10 incorrectly firing a below: 50 alert, or a negative baseline distorting change_percent).
   • If rule.threshold is NaN, negative, or non-finite, the rule is logged and skipped.
   • If baseline (oldFloat) exists but is NaN or negative, it is logged and skipped.
3. No Errors Thrown:
   • The function remains pure, resilient, and non-throwing. It gracefully accepts malformed or null array inputs (null or non-array rules, oldBalances, newBalances, or array elements with null items) without throwing exceptions, ensuring long-running streamAccount and createBalanceAlert polling loops remain stable.
4. Consistent Null Baseline Handling:
   • When no baseline exists (oldFloat === null), below and above evaluate against the initial balance alone (firing once on initial crossing if past threshold), while change_percent consistently does not fire (changePercent = null) because percentage change requires a non-zero baseline.
   • Explicit null baseline entries in oldBalances are handled consistently with empty baselines.

Acceptance Criteria Covered

• NaN and negative balance values are detected and logged or skipped.
• null baseline values are handled consistently across all conditions.
• Tests cover invalid balance data (NaN new balance, negative new balance, NaN baseline, negative baseline, non-finite values, null arrays, and malformed thresholds).
• Alert types and crossing semantics are completely unchanged.

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