Expose detached committed snapshots and explicit canonical construction ownership. Preserve scoped publication and rollback, share Box decoration, and reuse completed Flex/Grid work only under proven constraints.
Make TP the sole owner of live-buffer text-property publication, mount spans, scoped diff execution, and transaction rollback. Ebox now computes layout owners and retained surface plans, publishes handle/viewport/theme/scroll changes through TP, and keeps its mirrored runtime state transactionally consistent. Remove the former Ebox marker/index/patch executor instead of preserving a second mutation path.\n\nVerification:\n- make ci EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs\n- make package-lint-install EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs\n- strict byte compilation passed for 16 files\n- Ebox production has no tp-- private calls or marker writers\n- TP production has no Ebox dependency
Assign retained TP identity before layout and emit pure, runtime-free surface plans with exact character and text-property equivalence. Keep live publication unchanged for the staged cutover and add focused surface, package, docs, and CI contracts.\n\nVerified: make check EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs\nVerified: WERROR byte compilation for all 16 active Lisp files\nVerified: focused ebox-surface checkdoc has zero warnings
