GEOS implementation retirement

This audit covers the geometry paths identified for replacement in Terrio, starting from 07182d56e06f9cbf685a6f992df6411cbe99e223. It distinguishes implementation provenance from executable compatibility references. It is a technical inventory, not a repository-wide legal clearance.

Replacement inventory

Original path	Current implementation and evidence
`ops/simplify.rs`	Pinned JTS 1.20.0 tagged-line simplifier and predicates; source mapping and observations.
`ops/hull.rs`	JTS convex scan and concave erosion, with JTS point and constrained polygon triangulations in `jts_delaunay.rs` and `jts_cdt.rs`.
`tiles/valid.rs`: validity	Separate JTS integer-grid validity checker in `tiles/validity.rs`.
`tiles/valid.rs`: MakeValid and private/shared helpers	Entire file removed. Independently authored `tiles/repair/` imported mechanically from the isolated implementer's delivery. Process and validation, import ledger.
`tiles/vector.rs`: clipping-envelope calculation	JTS `OverlayUtil` / `RobustClipEnvelopeComputer` port in `tiles/overlay_envelope.rs`.
`tiles/vector.rs`: shared box candidates	Adapter to the existing `rstar` dependency in `tiles/boxes.rs`; the retired repair's grid helper is removed.
`ops/vector_geom.rs`: STR packing	JTS packing in `ops/strtree.rs`, preserving all IDs with documented equal-key ambiguity.
`pointcloud/filters/hexbin.rs`	Calls the replaced shared simplifier; no separate simplifier implementation.

The two implementation stages remain separate commits. The second stage includes the complete repair retirement, independent design and exposure records, approved input manifest, import hashes, behavioral fixtures and production comparison reports. One-off agent launchers, package scaffolding and verbose setup records are archived rather than included as maintained tooling. Root and crate NOTICE distinguish the EDL-1.0 JTS ports from the independent MIT repair. The CLI guide, README and acknowledgements describe the final implementation rather than the retired port.

Remaining references and boundaries

tiles/vector.rs retains its empirically tuned crossing/omission predictor. Its original probes reported about 97% agreement with GEOS 3.14. The predictor models observed clipping failures and is not a full OverlayNG port. The JTS clipping envelope is explicitly attributed. Current production comparisons separately report 25 unchanged synthetic feature-key/zoom differences; they are checked against frozen geometries rather than waived by identifier.
tiles/clip.rs uses Sutherland-Hodgman rectangle clipping. Its GEOS reference explains why a clipped ring can remain one ring instead of multiple polygons.
Shapefile ring organization describes GDAL's normalization and ring-start behavior; linear referencing explicitly documents independent mathematical projection/distance formulas and MIT GDAL adapters. No additional GEOS source port was identified in these paths by this inventory.
Public ops/topology.rs::make_valid uses GeoRust geo; it is a separate API from the retired tile repair. It did not require replacement for this task.
Reference collectors, conformance scripts and fixtures intentionally retain GEOS names, version numbers and executable calls. Production repair replay tests need no native GEOS installation. The optional GDAL backend invokes an installed external GDAL program, which may itself use GEOS.
+proj=geos and the CRS module's Geos type mean the geostationary satellite projection. They are unrelated to the GEOS geometry library.

cargo metadata --locked --offline found 385 packages in the current workspace resolution, with no GEOS or geos-sys package. The two r-efi versions advertise an LGPL alternative alongside MIT/Apache alternatives; that license expression is not a GEOS dependency. No dependency was added by either replacement. The freshly built Linux CLI's ELF dependencies contain only the platform C/math/compiler runtimes, with no GEOS or GDAL library. This is evidence about this resolution and artifact, not every future feature selection or external program on a user's machine.

Compatibility limits

The independent repair passed 51 captured kernel cases, 50 supported encoder cases and 4,500 generated kernel comparisons. Seven county feature instances have a documented difference in which polygon owns an identical collinear ring after integer truncation. These are invalid decoded geometries, not valid geometry matches. Oriented ring multiplicity, exact tile-grid coordinates and all non-collinear polygon groups must agree for that classification.

Eight generated full-range i32 inputs caused candidate-only encoder overflows because the replacement enumerates rings differently. The production encoder now returns an explicit error for an unrepresentable signed cursor delta. The kernel still supports those input ordinates; reference traversal order is not part of its contract. The largest stress inputs completed locally, but their optional GEOS differential run was stopped without a result. The installed Rust toolchain was 1.99; the declared 1.90 MSRV has not been exercised locally.

Release follow-through

The known source-replacement inventory above is complete. Before distribution, reviewers should assess both provenance records and the recorded behavior limits, and run the repository's release dry run on supported platforms. Its packaging workflow stages the notices into Python artifacts, CLI archives and the npm package; the crate also carries its synchronized NOTICE.

Retiring source changes future builds. Existing releases and their notices need a separate inventory of what was actually shipped and a maintainer decision on any corrective distribution steps. This patch does not rewrite Git history, withdraw releases or purport to settle past distribution obligations. Keep the audit evidence and upstream JTS copyrights with future releases.