Raw Slate should not own Markdown and table product packages

Problem

The Slate v2 pagination architecture lane drifted into shipping raw Slate Markdown and table packages. That crossed the ownership boundary: Markdown syntax policy and table feature behavior belong in Plate or app packages, not in unopinionated Slate.

Symptoms

• Raw Slate package directories existed for Markdown parse/serialize/input rules and table maps/commands/cell selection.
• TypeScript path aliases made those packages part of the workspace graph.
• The pagination plan and PR reference described them as accepted package surfaces.

What Didn't Work

• Copying Lexical's package shape too literally. Lexical's Markdown package is useful evidence for grouping transformers, but Slate's ecosystem boundary is different because Plate is the product package layer.
• Treating package tests as validation. The tests proved the stubs could work; they did not prove raw Slate should own that scope.
• Calling the packages "opt-in". Optional product packages still bloat the raw Slate API and teach the wrong extension boundary.

Solution

Hard-cut the raw Slate package surfaces:

• delete the Markdown and table package directories
• remove their TypeScript path aliases
• remove PR-plan language that presents them as raw Slate packages
• document the corrected boundary:
  • raw Slate owns schema/spec policy, transforms, selection primitives, normalization, clipboard/input hooks, and layout projection primitives
  • Plate/app packages own Markdown parse/serialize/input rules, table maps, table commands, cell-selection UX, and GFM hooks

Keep Slate examples as local proof fixtures. Do not promote example-local Markdown/table logic into a raw Slate product package.

Why This Works

The useful abstraction is the substrate, not the product feature. Pagination, selection, and rich layout still need table-like geometry and Markdown-shaped fixtures, but Slate can support that through generic structured blocks, app provided boxes, transforms, and selection/layout primitives.

Plate can then build the richer Markdown and table packages without forcing raw Slate to pick product syntax, table UX, menu behavior, or full GFM semantics.

Prevention

• When a feature sounds like a product editor capability, ask whether Plate is the better package owner before adding a raw Slate package.
• Treat external editor packages as evidence, not as package templates to copy.
• A raw Slate package should pass the substrate test: it must be useful without committing to a product schema, syntax, menu, or UX policy.
• Do not let tracer tests legitimize the wrong ownership boundary. Tests prove behavior, not scope.

Related Issues

• Slate v2 migration backbone lanes need browser contracts before completion
• Slate v2 Yjs readiness needs core contracts before package work