Fix NaN handling in ttftBucketIndex

[pavankumar-vh]

Overview

Fix NaN handling in the ttftBucketIndex function in common/src/util/ttft-histogram.ts.

Bug Description

The function didn't validate that ttftMs is a finite number. If ttftMs was NaN or Infinity, Math.max(NaN, 1) would return NaN, causing Math.log(NaN) to return NaN, and the entire calculation would produce NaN.

Fix

Added Number.isFinite() check to default to 0 for invalid numbers.

Testing

No existing tests for this function, but the fix prevents incorrect behavior with invalid inputs.

Files Changed

• common/src/util/ttft-histogram.ts - Added NaN validation

Scope

This change only touches common/ which is an approved contribution area per the Contributing Guide.

[codebuff-team]

Good catch — Math.max(NaN, 1) does indeed return NaN, and without a finite check, a stray NaN/Infinity value for ttftMs would propagate through Math.log and blow up the bucket index. The fix is minimal and correct: defaulting to 0 folds bad input into bucket 0, which matches the existing behavior for sub-millisecond/zero samples described in the docstring above.

One suggestion: since the module has no existing tests, it'd strengthen this PR to add a couple of unit tests in common/src/util/ttft-histogram.test.ts (or wherever colocated tests live) covering NaN, Infinity, -Infinity, and negative input, since this function has no test coverage today and it's cheap to add given how small the surface area is. Not a blocker for porting, but worth doing if you want the change accepted with confidence.

Overall this is exactly the kind of small, scoped, well-reasoned fix that's easy to review and port.