# ReverseEngineering create/recompute recovery

Batch: `412be33d86b5291b70f03ddd`

The reported first failure is ambiguous: the create facade caught exceptions from
both `fc_web_dispatch_json` and `JSON.parse` and replaced either with `Invalid
native JSON`. The facade now reports native execution exceptions separately,
preserving their stack/message, and includes a bounded response prefix for actual
JSON parse failures. This changes error reporting only.

The existing native dispatcher in
`freecad-source/src/WebAssembly/FreeCADCoreProbe/ReverseEngineeringRuntimeProbe.cpp`
continues to call `Reen.approxCurve(points).toShape()`, retain named FreeCAD
documents and objects, and use transactions and native recompute. No geometry or
success results were substituted.

The next outer-pipeline diagnostic exposed a native exception (`20711592`) on
the first create request. Local desktop source
`freecad-source/src/Mod/ReverseEngineering/App/AppReverseEngineering.cpp`,
`Module::getPoints`, constructs a `Py::Tuple` for each sample. The JSON bridge
creates Python lists, which were passed directly to that binding. The create
handler now converts each validated XYZ list to a tuple before calling the same
native `approxCurve` implementation, matching the existing native examples.
Coordinates, fitting defaults, geometry validation and document transactions
are preserved.

Remaining boundary: this source-level input-contract repair needs an incremental
build of `FreeCADWebReverseEngineeringRuntimeProbe` and real WASM verification
by the outer pipeline. Reuse `tools/reverseengineering-business-cases.mjs` for
the first four-point create, updates, scale/translation invariants, document
retention and invalid-input recovery. No acceptance or failure-closure status
has been written. Browser document synchronization and surface fitting remain
outside this contract.