Foundations PL4 0.0.2a.R2.3 — second correctness audit

• Stage ADD-mode item, fluid and legacy FE extraction in persistent escrow before calling the destination. A destination that throws before accepting resources no longer discards the extracted buffer.
• Enforce the shared 32 KiB preview budget for fallback item/fluid previews as well as full previews. Numeric rows survive visual-budget exhaustion; bounded component identities remain stable.
• Reject layout snapshots above the shared 32-element limit before decoding individual entries.
• Add native regression cases for failing destination insertion, save/retry conservation, preview exhaustion/key stability and layout array limits.

This is a focused correctness update for the 1.21.1 and 26.3 branches. It does not establish compatibility with other Minecraft versions or untested optional-mod releases. Providers that mutate resources and then throw without reporting what they accepted remain outside the conservation guarantee.