Keep reconstruction coverage intervals inside fitted wall extents #96

At PR #20 head 1c2686b, recon/recon/coverage.py:246-253 floors the first cell to a half-foot boundary and allows the last cell beyond the fitted extent. observed at lines272-277 exports each as a complete interval.

For a fitted start at s=0.10m, the first cell starts at0 and samples near0.038m and0.114m. Its first sample lies outside the fitted stretch. If an older, longer scan-bundle baseline is retained by recon/recon/scene.py:56-59, an outside surface can support an observed interval on wall the fit did not establish. Without that longer baseline, server wall-backing checks reject positions outside the wall segment, so the unsafe outcome is conditional.

Generate only fully contained cells or clip and independently sample partial boundary regions. Test unaligned endpoints, nearby surfaces beyond each endpoint, and a retained longer baseline. Exported observation must not exceed the evidence actually sampled inside the fitted extent.

Source: #20 (comment)

Deferred by the manager to Hunter's team as a P2 follow-up for the draft reconstruction handoff. The conditional unsupported-coverage consequence must remain visible until repaired.