Paint independent regions while widgets under change are held back

evidence/frame-publication-20261006/README.md

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+# Independent frame publication
+
+Native Screen asks its existing preparation owner for deferred Widget roots.
+Compositor derives held rectangles from committed geometry, retains their damage,
+and publishes other spans through its existing chops and inline formats.
+BackgroundScreen borrows the same admission during the synchronous render.
+The original callback queue admits senders outside held subtrees; containers of
+a held subtree also wait. Screen reports the exact acquired roots only after an
+actual non-None display. The application writer remains responsible for flush.
+
+Mutation roots borrow original committed placements during arrangement. Native
+box measurement uses those placements rather than descending into changing
+children. The existing scene map remains the geometry owner. No second queue,
+timer, damage store or compositor is introduced.
+
+The shared Toad contract is `_prepare_compositor_refresh() -> tuple[Widget, ...]`,
+`_layout_mutation_roots() -> tuple[Widget, ...]`, and
+`_on_frame_published(deferred_roots: tuple[Widget, ...])`. Parent owns Toad #482.
+
+`before.json` uses the existing refactor-audit Package parser over all 249 native
+production modules and 461 test modules, with zero omissions. Its 259 lexical
+sites identify definitions and references; dynamic subclass and callback
+resolution was read semantically, not inferred from absence.
+
+This remains a draft pending the matching Toad application journey owned by
+Parent. Native checks passed: 17 in 1.76s for batch/publication and scene-damage
+semantics; then 12 in 1.69s after completing polymorphic sender/backdrop admission,
+including inline, translucent, mutation/hit geometry, quiescence and reparenting.
+The first focused run refused an ambient-App sidebar callback; the receiver now
+owns admission. A later test incorrectly expected a Label at an original cell
+owned by its container; the control now compares the actual pre-mutation hit.
+Both original negative tool outputs remain in the session. Logs here retain the
+final successful checks and the intermediate hit assertion refusal.
+
+Parent's first matched source App at 225c did not finish and was joined. Its
+successful stack observed held-callback idle work; its later empty stack file
+is not evidence. The held queue entry called check_idle on every pass. That
+wake-up is deleted, and held-only damage no longer resumes the original timer.
+No new timer or wakeup mechanism was introduced. New source still requires the
+changed matching application check; no latency improvement is claimed.
+
+Callback scope is polymorphic: MessagePump and Screen await the entire frame;
+Widget borrows its own original screen geometry, including backdrops. InvokeLater
+is delivered to the receiver's original queue before sender admission. Container
+callbacks cover descendants as well as roots enclosing the sender. Mutation
+placements also protect hit lookup from a sibling's still-unpainted overlap.
+`after.json` parses the staged complete production/test tree with zero omissions;
+it records the actual declaration/MRO hooks and lexical consumers. The frozen
+textual-native-subtree-strips checkout is unchanged.