Make prepared software presentation atomic

[conxlgtm]

Summary

• Make asynchronously prepared software frames latest-wins transactions with typed presentation outcomes.
• Revalidate redraw identity, configure state, geometry, and reservation ownership immediately before commit, without emitting Wayland requests for rejected attempts.
• Stage throwing commit work before shared-memory buffers become busy, then execute callback, feedback, attach, damage, commit, and bookkeeping without throwing.
• Apply the same precommit staging boundary to popup software draws and external-buffer presentation so rejected attempts cannot emit frame or feedback requests and committed frames cannot be reported as failed.
• Preserve redraw progress after cancellation, supersession, and precommit failures, and prevent wrapped redraw generations from revalidating stale work.
• Expose atomic presentation feedback on simple software draws and verify forwarding request recording through public-only live tests.

Why

• Preparation can suspend while a newer redraw, configure, close, or cancellation makes the original frame stale.
• Rejected or failed presentations must not partially emit a surface transaction or strand dirty content without a replacement redraw.
• Shared-memory ownership becomes irreversible when a buffer is marked busy, so every recoverable failure must occur before that point.
• External-buffer callback and feedback requests are likewise irreversible protocol work, so copied model state and result validation must succeed first.

Validation

• nix develop -c env CC=clang CXX=clang++ swift run wck test unit --verbose
• nix develop -c env CC=clang CXX=clang++ swift run wck smoke headless -- wck test request-paths
• nix develop -c env CC=clang CXX=clang++ swift run wck smoke headless -- wck test integration-public-api --verbose
• Focused transaction and request-recorder TSan: 70 tests in 6 suites passed with no sanitizer diagnostics.
• Final popup, external-buffer, model, and feedback changed-path TSan: 33 tests in 4 suites passed with no sanitizer diagnostics.
• nix develop -c env CC=clang CXX=clang++ swift run wck ci cheap --verbose
• nix develop -c env CC=clang CXX=clang++ swift run wck ci required --verbose
• nix develop -c env CC=clang CXX=clang++ swift run wck protocols verify-generated
• nix develop -c env CC=clang CXX=clang++ swift run wck api verify
• nix develop -c env CC=clang CXX=clang++ swift run wck docc verify
• Serialized final-tree full-project TSan completed all 1,987 tests but exited nonzero with five warnings, all rooted in unchanged EventBroker.swift; no warning referenced a changed presentation or request-recorder path.