[fdalmaso]

When an edge-use implantation subdivided a boundary leaf containing polygon edges, Rust created the children and then returned Unported(SmFace::GetSurface). This completes that branch of SmTrimSrfCache::SubdivideNode: each polygon is reimplanted in child 1 and child 2 using its original surface, endpoints and tolerance.

The parent polygon list stays intact, iteration starts at its head, and each child's prepend order matches C++. Mixed edge-use lists retain native behavior. The cache keeps an owned evaluation snapshot of each implanted polygon's original surface, alongside its endpoints and tolerance, and carries that data through map_handles. Callers reimplant after editing an edge or its original surface, following the existing edge-use snapshot pattern.

Coverage adds 128 separate fixed-seed cases and 4 fixtures: repeated U/V subdivision, crossing and degenerate segments, mixed lists, different original/cache surfaces, handle remapping, tolerance cutoffs, and native zero/negative tolerance construction. All 630 existing cases remain passing with their value coverage preserved. The reference is still upstream c9c5979; no newer C++ version is required.

Validation after merging main 53872b3d0:

• cargo fmt --all --check and cargo clippy --workspace --all-targets -- -D warnings: pass.
• Native runner lint check, cargo clippy --profile difftest -p difftest --lib --features cpp -- -D warnings: pass.
• cargo test -p solidcore: 2,229 passed, 0 failed, 1 existing ignored test.
• cargo check -p solidcore --target wasm32-unknown-unknown: pass.
• cargo test --profile difftest -p solidcore-ffi --features cpp surface_trim_srf_cache: 5 passed, including truncation, bad node indices, nonfinite data and zero/negative tolerance validation.
• Full native --green --jobs 4: 261 units, 251 pass, 10 partial, 0 failures. CI applies the exact-base artifact ratchet.

PASS surface.trim_srf_cache cases=762 passed=762 failed=0 deferred=0 max_rel_err=0e0 with_values=762 no_values=0 vacuous=0
difftest: 261 unit(s), 251 passed, 10 partial, 0 failed

No tolerance or absolute floor changed; no known mismatch or coverage waiver added. Reports remain untracked.

[bherbruck]

Approved by the automated first-pass review: CI green, mergeable, no CI/build/dependency file changes, no red-flag patterns in added code (process/network/env/unsafe outside FFI/blobs/hidden unicode), 0 known-mismatch entries added. Logic is gated by CI and the difftest merge queue.