ponder-lab / Hybridize-Functions-Refactoring / #2460

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Track suffix and prefix shape slices rank-independently so the descriptor survives unresolvable ranks (#762)

* Track suffix and prefix shape slices rank-independently

The numpy-shape descriptor was dropped at a slice whenever the source tensor's rank was statically unresolvable (a ⊤ context, or contexts disagreeing on rank): `narrowBySlice` required `sourceRank`, so the corpus `einsum_via_matmul` suffix slice `input_shape[-num_inner_dims:]` fell back to an untracked shape taint and the sink saw a null descriptor, never consulting `numpyOverShapeStaticness`. A pure suffix slice covers the last `k` dimensions regardless of rank, so it is now narrowed to negative indices that the verdict resolves against each context's own rank (out-of-range indices degrade to unprovable, mirroring Python's clamping); a pure prefix slice likewise needs no rank. Rank-resolvable slices keep the absolute path unchanged.

The BERT-style `get_shape_list` idiom itself (in-callee `.shape.as_list()`, element-wise `tf.shape` mutation, dual returns) turns out to be tracked already: the caller-side extractor seed anchors the all-dimensions descriptor at the call site independent of the helper's internals. `testNumpyOnDynamicShapeThroughShapeList` pins that with a fixture distilling NLPGNN's helper verbatim, and `testNumpyOnDynamicTailAcrossRanks` pins the actual fix: a suffix slice over a mixed-rank source with a dynamic trailing dimension now declines, where the dropped descriptor previously permitted the crasher.

Closes #761.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M4XLK81HCB6Vp1WQiRPafR

* Preserve the descriptor under no-op and empty rank-free slices

A no-op copy slice (`[:]`) covers every dimension regardless of rank, so it now preserves the base descriptor instead of dropping it, and the empty prefix `[:0]` is likewise rank-independent (it covers nothing). The across-ranks pin now exercises all three rank-fr... (continued)

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