test: cover drag-reorder, per-editor validation, and a11y on stable stories

[zhawtof]

Summary

Adds the three highest-leverage testing gaps identified in the suite audit: end-to-end drag-reorder coverage, payload-level validation around the editor forms, and enforced a11y assertions on stable stories.

Why

The current suite catches type errors and core pure-function regressions, but leaves the most user-visible behaviors uncovered: dnd-kit dragging (zero tests, dep upgrades could silently break the headline UX), editor → Slack payload shape drift (factories validated to "has a type" but not to "Slack would accept it"), and a11y (`addon-a11y` installed but configured as `'todo'` everywhere). These additions are cheap, ride on the existing Storybook + Playwright/chromium infrastructure, and turn the validator dep that's already in production into a safety net.

What changed

• Drag-reorder play test in block-kitchen.stories.tsx — anchors on visible block text, dispatches `pointerDown` → `pointerMove` (clears the 4px activation distance) → `pointerMove` to drop target → `pointerUp`, then asserts `onChange` resolved with the reordered block types.
• Per-editor payload validation — new `expectLastOnChangeIsValid` helper in block-editor.stories.tsx plus three new play tests (Header, Markdown, Image) that type into fields and assert the resulting block validates. Existing section test now also asserts validity.
• Factory validation in unit tests — test/public-api.test.ts loops every `defaultPalette` and legacy variant through `toSlackBlocks → validateBlockKit`, the same path the runtime uses.
• a11y enforced — `a11y: { test: 'error' }` on Button, Palette, Toolbar, and TemplatePicker stories. BlockKitchen and BlockEditor stay on `'todo'` per the existing comment about theme-dependent contrast flags.
• Vitest config — vitest.config.ts inlines `@tightknitai/slack-block-kit-validator` so its extension-less ESM imports route through Vite's resolver. Node's pure ESM resolver rejected them; Storybook's Vite-backed browser project already handled them. One-line workaround for an upstream packaging quirk, no behavior change.

Test plan

• `pnpm typecheck`
• `pnpm lint`
• `pnpm test` — 217 passing (up from 199)

Notes for reviewer

• The drag-reorder test uses `fireEvent.pointerDown/Move/Up` rather than `userEvent.pointer` so it can explicitly set `isPrimary: true, button: 0, pointerId` — dnd-kit's `PointerSensor` rejects events that don't satisfy those checks, and `PointerEventInit` defaults `isPrimary` to `false`.
• The factory validation test deliberately throws with the failing variant id in the error message so a regression surfaces the exact broken factory rather than a generic assertion failure.
• The a11y flip only enforces axe on already-passing stories, so this PR does not fix any new a11y issues — it locks in the current good state.

🤖 Generated with Claude Code

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	block-kitchen	317a400	Commit Preview URL Branch Preview URL	May 16 2026, 05:21 PM