[lenzo-ka]

Defect

One-pass float32 variance estimates can serialize as zero or slightly negative. Direct serialized-array readers bypass the positive variance invariant established by gauden_t model loading, so KD-tree geometry, density splitting, MAP priors, and MMIE updates can produce non-finite results.

Fix

Add shared diagonal and full-covariance array floor helpers and apply them after affected computational reads. map_adapt honors -varfloor; other consumers use the existing 1e-4 evaluation floor. Raw serialized artifacts and copy/passthrough paths remain lossless. Add a CTest regression.

libclust/kdtree.c remains unchanged because its caller now establishes the invariant before log() and sqrt() computations.

Reader audit

Routed: inc_comp, kdtree, map_adapt, and MMIE norm.

Already protected locally: libmodinv/mod_inv.c, mllr_solve, bldtree, and make_quests.

Display/copy/initialization/template reads left lossless: printp, cp_parm, init_mixw, and the other norm rereads. The remaining mllr_transform and init_gau sites read means.

Verification

• cmake -S . -B build
• cmake --build build
• ctest --test-dir build --output-on-failure (1/1 passed)

This ports the landed boundary and consumer routing from pstrain PR #134.