Autoformat Coverage Pass

Goal

Add a surgical, fast-lane-only coverage pass for @platejs/autoformat focused on the last worthwhile non-rule seams:

• AutoformatPlugin.ts
• autoformatBlock.ts
• isPreviousCharacterEmpty.ts

Constraints

• No /react.
• No rule-table coverage.
• Keep the slice in normal *.spec.ts[x].
• Prefer real editor behavior for plugin contracts and tiny stubs for pure transform helpers.

Slice

1. Add a direct AutoformatPlugin spec for query veto, insertTrigger, and undo-on-delete array-match restore.
2. Deepen autoformatBlock.spec.ts for triggerAtBlockStart: false, allowSameTypeAbove, and single-character match safety.
3. Add one tiny isPreviousCharacterEmpty edge for empty-string ranges.
4. Stop unless a direct test exposes a real bug.

Notes

• Existing withAutoformat coverage already exercises most end-to-end mark and text flows.
• The remaining value is in the plugin override seam and a few pure autoformatBlock branches.