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Slate React Zero-Width Render Policy Proof Plan

docs/plans/2026-04-03-slate-react-zero-width-render-policy-proof-plan.md

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Slate React Zero-Width Render Policy Proof Plan

Goal

Work the renderer policy split honestly:

  • keep the future v2 target clear: line-break placeholders can move toward -only once IME proof exists
  • keep legacy Slate conservative: FEFF stays on the empty-block start-of-block line-break path until that IME proof exists
  • keep FEFF-like sentinel text for IME-sensitive non-linebreak zero-width cases

Working Hypothesis

The smallest honest legacy cut is:

  • codify the split in comments and tests
  • leave the legacy empty-block line-break path conservative for now
  • prove renderer shape and selection sanity without overstating what is known

Proof Priorities

  1. empty block line-break placeholder renders and still retains FEFF in legacy
  2. focus / selection on an empty block still works
  3. empty inline zero-width placeholder still retains FEFF

Phases

Phase 0

Freeze the proof seam and constraints.

Phase 1

Write red tests for renderer shape and selection safety.

Phase 2

Implement the smallest legacy renderer policy codification.

Phase 3

Verify, deslop, re-verify, architect review, cleanup.

Progress Log

2026-04-03

  • grounded the split against:
    • the approved bridge-tolerance proof
    • legacy string.tsx
    • legacy dom-editor selection behavior
  • added red tests for:
    • empty-block line-break placeholders rendering and retaining FEFF in legacy
    • FEFF retention for empty inline-edge zero-width placeholders
    • focus / selection sanity for an empty block
  • attempted to drop FEFF on the legacy line-break path
  • architect rejected that broader change because the evidence did not cover IME composition on the empty-block start-of-block path
  • narrowed the conclusion and restored legacy FEFF retention on that path
  • final result: legacy Slate keeps FEFF on the empty-block line-break path, while the future v2 policy line stays open for a stronger IME-backed split
  • architect verdict: APPROVE on the narrowed conclusion
  • deslop pass found no worthwhile simplification beyond the proof and comment
  • verification evidence:
    • zsh -lc 'yarn jest --config jest.config.js --runInBand --coverage=false'
    • zsh -lc 'yarn build:rollup'
    • zsh -lc 'yarn lint:typescript'
    • LSP diagnostics 0 on changed files
  • reusable note captured in: 2026-04-03-legacy-line-break-placeholders-still-keep-feff-until-ime-proof-exists.md