Slate v2 Phase 9 Anchor Matrix

Supporting plan. For current queue and roadmap truth, see master-roadmap.md.

Goal

Continue Phase 9 replacement-envelope expansion by widening the matrix for the anchor / projection family.

Scope

• add one current persistent-annotation-anchors row to the replacement compatibility matrix
• sync the scoreboard/docs if the row lands cleanly

Constraints

• no fake legacy twin
• use the matrix to record current replacement-candidate truth, not symmetry for symmetry’s sake
• verify through the cross-repo local runner on current port 3010

Progress

• added one current persistent-annotation-anchors row to the replacement compatibility matrix
• proved the expanded matrix through the cross-repo local runner
• synced the scoreboard and top-level v2 docs so the landed Phase 9 slice is visible in the roadmap stack
• verification:
  • bash ./scripts/run-cross-repo-local.sh 3010 /examples/rich-inline ../slate 3210 /examples/search-highlighting "yarn build:slate-browser:playwright && yarn exec playwright test playwright/integration/examples/replacement-compatibility.test.ts --project=chromium --workers=1"