Texture lookup previously acquired references implicitly, and mesh sections and
loader requests paired raw texture pointers with manual release paths. Separate
borrowed lookup from scoped acquisition and explicit load requests/waits to match
the piece data ownership API.
Store lcTextureRef in mesh sections and loader requests, retain references on
section copies, and reset worker-shared request handles on the UI thread before
completion, cancellation, or shutdown. Keep reference primitives internal and use
scoped acquisitions for merge validation. Remove redundant section initialization
and synth-notification resets, and document the resulting ownership contracts.
Validation: macOS Debug build, diff whitespace checks, and 30 offscreen lifecycle
checks covering reference copies/moves, texture dependencies, cancellation,
shutdown, merge conflicts, and existing piece ownership paths. Successful GPU
upload/rendering is not covered by the offscreen checks.