feat(mint): add @property type-check analysis to CSS audit

[nujovich]

Card: https://github.com/nujovich/mint-radar/issues/8

What

Extends the CSS audit with @property type-check analysis. A new STEP 13 in lib/prompts.mjs detects CSS @property registrations, validates them and their var() usages against the declared syntax descriptor, and reports violations as propertyTypeIssues. It builds on Mint's existing LLM-based audit pipeline — no new runtime parser needed.

Three rules are reported, most severe first:

Rule	Severity	What it catches
invalid-initial-value	warning	An initial-value that does not parse as the declared syntax, or a missing initial-value on a non-universal syntax. The browser rejects the whole registration, silently dropping both the type contract and the ability to transition.
fallback-type-mismatch	warning	var(--my-color, 14px) — a fallback whose type contradicts the registration, so it can never apply.
property-type-mismatch	suggestion	A registered property assigned where its declared syntax cannot apply (a <length> used in color). Reported only when unambiguous from the stylesheet alone.

Registrations declaring the universal syntax (*) are skipped — they are not type-checkable.

Why

@property adoption is growing (2.67% per Project Wallace 2026, driven by Tailwind v4). Mint audits colors, fonts, spacing, line-height, motion, layout accessibility, modern practices and overflow safety, but had no awareness of registered custom properties or their type contracts. Mismatches between a declared syntax and actual usage are a class of bug that neither ESLint CSS nor Stylelint targets natively, which reinforces Mint's positioning as a semantic auditor.

Milestones

• Milestone 1 — STEP 13 in lib/prompts.mjs: detect registrations, validate against the declared syntax, report violations
• Milestone 2 — PropertyTypeIssue interface + propertyTypeIssues on AuditReport in lib/types.ts
• Milestone 3 — surface results in the CLI summary and the playground
• Milestone 4 — lib/__fixtures__/at-property.css fixture covering one case per rule, plus tests
• Docs — the three rules in the README's CSS layout linting table, plus a subsection on @property type safety

Review fixes (bfa9a22)

The first commit shipped the prompt step alone, emitting an output shape of its own (propertyName / declaredSyntax / location / issue). Neither shared consumer can read that shape, so findings were produced by the model and then silently discarded: an empty severity badge, — as the anchor and a blank reason in the playground, and no entry at all in the CLI summary.

• align propertyTypeIssues with the contract every other lint category follows: selector, property, rule, severity, reason (plus propertyName and declaredSyntax as extras)
• split STEP 13 into the three named rules above, adding the invalid-initial-value check — the highest-value deterministic check, and the one previously missing
• drop the ad-hoc >> location separator in favour of discrete selector + property, mirroring layoutA11yIssues
• narrow the foreign-context rule to unambiguous cases to limit false positives
• register propertyTypeIssues in LINT_CATEGORIES (lib/audit-summary.mjs) — the single registry feeding both formatLintSummary in the CLI and collectLintGroups in AuditView, so one entry lights up both surfaces
• add a lint-contract test that parses the prompt's own <example> block and asserts severity / reason / anchor across all five lint categories
• remove the BUILD-PLAN-issue-8.md scratch file

Documentation (dbf0727)

The README's CSS layout linting section tables every category and its rules; @property was missing from it. Added the three rules to that table, a @property type safety subsection explaining why invalid-initial-value is the one to fix first and that universal-syntax registrations are skipped, and updated the audit step and section intro. The subsection's CSS sample is wrapped in prettier-ignore so the aligned trailing comments survive formatting, matching the existing convention in the Frankenstein example.

Verification

vitest        592 passed (25 files)
typecheck     clean
eslint        no warnings or errors
format:check  clean
check:pack    28 files reachable from bin

The CLI summary line renders 1 overflow · 2 property types, and the shared renderer receives severity=warning, anchor=@property --spacing-unit, reason=Registered as <length> but initial-value… where it previously got undefined for all three fields.

Note for #105

#105 also adds a step numbered STEP 13, at the same hunk in lib/prompts.mjs. Both PRs report MERGEABLE because each is diffed against main in isolation. Whichever merges second must renumber to STEP 14 to avoid a duplicated step number in the audit prompt.

How to test

npm test

node -e "import('./lib/prompts.mjs').then(m => console.log('STEP 13 present:', m.buildAuditPrompt('').content.includes('@PROPERTY TYPE CHECKING')))"

[nujovich]

All milestones complete. Ready for review when you are.

[nujovich]

All milestones complete. Ready for review when you are.

[nujovich]

All milestones complete. Ready for review when you are.

[nujovich]

All milestones complete. Ready for review when you are.