fix(@stdlib/blas/ext/circshift): validate k broadcast shape

[Planeshifter]

Description

What is the purpose of this pull request?

This pull request:

• fixes @stdlib/blas/ext/circshift silently accepting a non-zero-dimensional ndarray k argument instead of throwing, which has been failing the Node.js v16 job on the macos_test workflow deterministically on develop for weeks.
• when k is provided as an ndarray and no dims option is given, main.js passed k straight through to the base implementation without validating that it is zero-dimensional, contradicting the package's own documented contract ("an ndarray for k must be a zero-dimensional ndarray") and its own test suite.
• routes k through the already-imported maybeBroadcastArray helper (already used for the dims-provided branch) in both previously-unvalidated call paths, so a k with a non-zero-dimensional shape now throws instead of being silently accepted.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues: none. Discovered via automated monitoring of scheduled CI failures on develop, not a filed issue.

Questions

Any questions for reviewers of this pull request?

No.

Other

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Failing run: https://github.com/stdlib-js/stdlib/actions/runs/33173054715 (job Node.js v16, workflow macos_test; the same failure reproduces on every scheduled run of this workflow going back weeks — not a flake).

Symptom: circshift's own test suite reports 6 failing assertions: circshift(x, k) and circshift(x, k, {}) do not throw when k is an ndarray with shape [4], [2,2,2], or [0] against an x of shape [2,2].

Root cause: in lib/main.js, when k is ndarray-like and no dims option is supplied, the function assumed (per an inline comment) that k was already zero-dimensional and passed it straight to base() with no validation — in both the 2-argument call form and the 3-argument form when opts lacks a dims property.

Fix: route k through maybeBroadcastArray( k, [] ) in both unvalidated branches — the same helper already used one branch over for the dims-provided case, just against a fixed target shape of [] (zero dimensions) instead of the non-core shape. For an already-valid zero-dimensional k, maybeBroadcastArray returns the identical object reference, so the happy path is unchanged; for any higher-rank k, it throws.

Validation: local node_modules are not installed in this environment, so make test/make lint-pkg could not be run directly. Three independent adversarial reviews were performed against the diff and the package's own test suite, docs, and TypeScript declarations:

• Correctness reviewer: approved. Traced the fix through maybe-broadcast-array and broadcast-array by hand and by direct execution (no test runner available, so the module was exercised directly), confirming all 6 previously-failing assertions now throw and no currently-passing assertion in the package's test suite regresses.
• Regression-scope reviewer: approved. Confirmed the diff touches only this one file and these two branches; no other caller in the repo passes a non-scalar k without dims; README and docs/repl.txt already document the enforced invariant; no public API change.
• Style reviewer: approved. Matches existing formatting, delegates error construction to the existing helper (no new hand-written throw / no template-literal error messages), copyright header untouched.

Reviewer notes: non-blocking — the broadcast helper raises a generic Error rather than a more specific TypeError, and the top-of-file JSDoc @throws list doesn't enumerate the broadcast-incompatibility error (a pre-existing gap on the neighboring dims branch, not introduced by this change). Left as-is for consistency with the existing dims-provided branch.

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• Read, understood, and followed the contributing guidelines.

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This PR was found, diagnosed, fixed, and validated autonomously by Claude Code as part of a scheduled CI-failure-monitoring routine, including an independent three-reviewer adversarial validation pass. A human should still review before merging.

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
blas/ext/circshift	$\\color{green}263/263$ $\\color{green}+100.00\\%$	$\\color{green}20/20$ $\\color{green}+100.00\\%$	$\\color{green}1/1$ $\\color{green}+100.00\\%$	$\\color{green}263/263$ $\\color{green}+100.00\\%$

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

[kgryte]

Isn't this a duplicate?

[Planeshifter]

Confirmed — #14228 already covers this exact fix for circshift (and additionally sort/sorthp, which share the same defect). That PR has been open since 2026-08-13 and is still unmerged. Closing this in favor of #14228.

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