CODE review: bounded complete-buffer BAO proof

Review the additive cyber_bao::proof API on exact Radio parent b933829cbe273d2f31fe75ca83125f3ddd8917a2. The frozen PLAN was approved by a fresh Opus session. This CODE review sees the actual implementation and its tests; PLAN approval is separate. Return APPROVE or REQUEST CHANGES with concrete blockers separated from finite advice. No source edits, commit or merge by the reviewer.

The three production changes are one module declaration and two new source files. They compose the merged RangeTraversal and GroupHasher without changing kernels, legacy readers, dependencies or features. This is an additive minor API reaching Radio's soft3 rung; it is not release acceptance or complete foundation row 4. The future Kadek adapter reaches Cyb separately and is outside this implementation. No license, canon or specification text changes are included. Public Rustdoc is the new carrier, error, work, output and lifetime contract.

Trust is conditional on the supplied complete root and size. Canonical field-word checks precede arithmetic, exact EOF alone seals the immutable borrowed result, and output replays one geometry item per call. Whole selected groups can extend outside the request. The future Kadek adapter must retain its BaoAnchor association, charge verification/output/copy and own bounded storage before publishing ranges. This API authenticates neither a caller-invented particle association nor a first partial download. No network, serialized anchor or generic budget is added.

Review targets: canonical-word order/offsets, ROOT and absolute chunk counters, frontier stack correspondence, group completion followed by a later parent, one bounded action per call, sticky error/strict EOF publication, independent output coordinates and unforgeable borrowed view. Empty-file verification has four actions and no output; nonempty-file empty requests are rejected. Geometry admission is not a promise that a host can allocate a maximal admitted group.

The readable packet includes complete changed sources/tests, full relevant owning geometry/reducer/backend/carrier and consumer contracts, exact primary excerpts, approved PLAN/finite cases/review, seal sources and diagnostic classifications, fixture provenance and gate summaries. Raw command receipts and every source epoch are in the compact execution audit and independently replayable against exact Git objects. It includes the real initial invocation/cache incidents and current-parent negative comparisons; it does not disguise them as successful gates.

Omitted from this bounded review input: bulk locks/metadata, unrelated workspace runtime/network sources, full prior audit archives, most verbose gate raw output, compiled targets and the rest of primary repositories outside labeled excerpts. Their identities remain indexed by the audit and frozen research. The reviewer has not seen those omitted bodies. Root independently verifies the full raw/source capsule. Cached registry and external consumer inventory are historical observations, not current whole-product closure or hosted CI success. No 32-bit runtime or allocator-free no_std final-link claim is made.