refactor: add isnan guards

[Planeshifter]

Description

Propagating fixes merged to develop between 2026-07-06 15:53 -0700 and 2026-07-07 00:50 -0700 to sibling packages.

refactor: add explicit isnan guards — 2671115

Propagates the explicit isnan guard pattern from 2671115 ("refactor: add explicit isnan guards" in pareto-type1/{mean,median}) to sibling distribution packages, replacing implicit reliance on NaN <= 0.0 evaluating to false with explicit isnan( alpha ) || isnan( beta ) rejection. For betaprime/mode, the fix is not defensive-only: with the old guard, mode( 0.5, NaN ) returned 0.0 instead of NaN, because the follow-up alpha < 1.0 branch fired past the failed rejection.

Target packages:

• stats/base/dists/gamma/{mean,mode,variance,stdev,entropy}
• stats/base/dists/beta/{mean,median,mode,variance,stdev,skewness,kurtosis,entropy}
• stats/base/dists/f/{mode,variance,stdev,skewness,kurtosis}
• stats/base/dists/invgamma/{mean,mode,variance,stdev,entropy}
• stats/base/dists/betaprime/{mean,mode}

Related Issues

No.

Questions

No.

Other

Validation

• Pattern search scoped to lib/node_modules/@stdlib/stats/base/dists/*/{mean,median,mode,variance,stdev,skewness,kurtosis,entropy,mgf}/lib/main.js.
• Two independent opus validation agents read each candidate file end-to-end and confirmed the defect present, the fix applies verbatim, and no upstream validator already rejects NaN.
• Sonnet style-consistency pass confirmed each patch's isnan require placement (first in // MODULES //), guard-block indentation, parameter-order preservation, and threshold preservation match the source commit and the existing already-fixed sibling files (t/entropy, rayleigh/entropy, triangular/entropy, weibull/entropy).
• Each modified file re-read after patching to confirm exact match with the approved diff.

Deliberately excluded

• Sites where the guard uses >= (arcsine, uniform) — 9 files. The pattern signature differs from the source commit and the maintainer intent for >= bounds is not established by 2671115.
• Sites already delegating to a NaN-safe sibling (e.g. lognormal/stdev, t/stdev, chisquare/median).
• Sites already guarding with !isInteger(...) / !isNonNegativeInteger(...) (hypergeometric, discrete-uniform families), which reject NaN inherently.
• stats/base/dists/pareto-type1/* — source of the fix; already covered.
• All other source commits from the 24h window: grammar-fix propagation (547176ec, 9c313057) had zero remaining unfixed sites in the repo; ternary-parens propagation (563772fc) had zero remaining unfixed sites; dlast-index-of/slast-index-of collapse (ba80db9c) — sibling last-index-of packages already use return N - 1 - idx;; Float16Array index-signature fix (6b88a637) — pattern does not extend to Complex64Array/Complex128Array/BooleanArray (non-native, no numeric index access).

Checklist

• Read, understood, and followed the contributing guidelines.

AI Assistance

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Disclosure

This PR was authored by an automated stdlib fix-propagation routine: the last 24h of commits merged to develop were parsed for propagatable fix patterns; each candidate pattern's structural signature was searched across sibling packages; each candidate site was reviewed by two independent opus validation agents and a sonnet style-consistency agent, with only sites passing all three advancing to the propagation branch. Each patch was hand-verified against the approved diff before commit.

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Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/beta/entropy	$\\color{green}202/202$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}202/202$ $\\color{green}+100.00\\%$
stats/base/dists/beta/kurtosis	$\\color{green}207/207$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}207/207$ $\\color{green}+100.00\\%$
stats/base/dists/beta/mean	$\\color{green}195/195$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}195/195$ $\\color{green}+100.00\\%$
stats/base/dists/beta/median	$\\color{green}125/125$ $\\color{green}+100.00\\%$	$\\color{green}8/8$ $\\color{green}+100.00\\%$	$\\color{green}1/1$ $\\color{green}+100.00\\%$	$\\color{green}125/125$ $\\color{green}+100.00\\%$
stats/base/dists/beta/mode	$\\color{green}192/192$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}192/192$ $\\color{green}+100.00\\%$
stats/base/dists/beta/skewness	$\\color{green}201/201$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}201/201$ $\\color{green}+100.00\\%$
stats/base/dists/beta/stdev	$\\color{green}201/201$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}201/201$ $\\color{green}+100.00\\%$
stats/base/dists/beta/variance	$\\color{green}200/200$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}200/200$ $\\color{green}+100.00\\%$
stats/base/dists/betaprime/mean	$\\color{green}203/203$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}203/203$ $\\color{green}+100.00\\%$
stats/base/dists/betaprime/mode	$\\color{green}206/206$ $\\color{green}+100.00\\%$	$\\color{green}12/12$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}206/206$ $\\color{green}+100.00\\%$
stats/base/dists/f/kurtosis	$\\color{green}210/210$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}210/210$ $\\color{green}+100.00\\%$
stats/base/dists/f/mode	$\\color{green}195/195$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}195/195$ $\\color{green}+100.00\\%$
stats/base/dists/f/skewness	$\\color{green}207/207$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}207/207$ $\\color{green}+100.00\\%$
stats/base/dists/f/stdev	$\\color{green}208/208$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}208/208$ $\\color{green}+100.00\\%$
stats/base/dists/f/variance	$\\color{green}207/207$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}207/207$ $\\color{green}+100.00\\%$
stats/base/dists/gamma/entropy	$\\color{green}202/202$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}202/202$ $\\color{green}+100.00\\%$
stats/base/dists/gamma/mean	$\\color{green}195/195$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}195/195$ $\\color{green}+100.00\\%$
stats/base/dists/gamma/mode	$\\color{green}203/203$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}203/203$ $\\color{green}+100.00\\%$
stats/base/dists/gamma/stdev	$\\color{green}196/196$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}196/196$ $\\color{green}+100.00\\%$
stats/base/dists/gamma/variance	$\\color{green}192/192$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}192/192$ $\\color{green}+100.00\\%$
stats/base/dists/invgamma/entropy	$\\color{green}201/201$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}201/201$ $\\color{green}+100.00\\%$
stats/base/dists/invgamma/mean	$\\color{green}192/192$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}192/192$ $\\color{green}+100.00\\%$
stats/base/dists/invgamma/mode	$\\color{green}195/195$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}195/195$ $\\color{green}+100.00\\%$
stats/base/dists/invgamma/stdev	$\\color{green}196/196$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}196/196$ $\\color{green}+100.00\\%$
stats/base/dists/invgamma/variance	$\\color{green}196/196$ $\\color{green}+100.00\\%$	$\\color{green}10/10$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}196/196$ $\\color{green}+100.00\\%$

The above coverage report was generated for the changes in this PR.