feat(Schonhage): make native box products callable from ET records #2335

Continue #1394 from the complete routed box product #2332. Owner/session codex-root-3sum-20261102-continuation; branch work/three-sum-callable-box-20261102 from341bca745. Existing supplier branches stay unchanged.

Implement an actual callable standard WordRAM box product above a runtime caller base, using the checked memory-window compiler. Its input is original zero/one matrices, raw query occurrences and the ordinary threshold. Compute the virtual modulus from original dimensions; derive logarithmic width/polynomial window from the block regime rather than assuming source fits. Normalize the restored original input including the threshold and the exact answer span. Prove caller-safe execution with arbitrary dirty scratch, exact request-order products, full original-input restoration, caller frame, charged setup/translation/normalization/halt and the finite D^(-8/125) bound. Reuse existing native setup/return code where its semantics match. Add meaningful initialized/dirty-memory clients.

If the existing prepared-record APIs permit a bounded adapter, connect one actual prepared ET record by executing the changed level/threshold/length writes and real invocation; otherwise preserve that concrete next dependency prominently. The complete ET controller/callee replacement, aggregate cost and asymptotic absorption, native parameter retuning and ordinary-3SUM1.9992 remain open in #1394. Do not claim a callable milestone completes that endpoint. Independent correctness/API/resource review and all six project gates are required before integration; no curated abstract change expected.

Two read-only workers investigate the source admission bound and the existing record ABI. All source edits/build outputs are owned by root in this checkout. AI assistance: OpenAI Codex.