Why: continuation of the aesthetic detector series. Mirrors
detectMixedSiblingCornerRadius (53435bf7) for the padding axis. Three
cards with padding 16 / 16 / 20 looks ragged on canvas; the existing
sibling-inconsistency detector covers cards-vs-cards but dedupes
against cornerRadius and other props so the padding outlier
sometimes drops.
What: detectMixedSiblingPadding normalises padding values to a
4-tuple [top, right, bottom, left] before comparison, so
padding: 16 → [16,16,16,16]
padding: [12, 24] → [12,24,12,24] (CSS 2-tuple shorthand)
padding: [16,16,16,16] → [16,16,16,16]
all compare equal and don't trigger false positives. Modal value
collapses back to a scalar when all four sides are equal so the
suggested fix matches the model's preferred shorthand.
Same 60% modal-majority threshold as the cornerRadius detector —
1-1-1 three-way splits are skipped because there's no canonical value
to suggest. Same divider / spacer skip and same-type-and-role grouping.
Wired through detectAllIssues + index.ts exports + the
debug_validation_report MCP categories enum.
6 new tests cover: number shorthand outlier, number-vs-array
equivalence, 2-tuple-vs-4-tuple equivalence, 1-1-1 split skip,
mixed-role groups skipped, no-padding siblings excluded from modal.
57 / 57 diagnostics tests pass (was 51; +6).
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