[lmeyerov]

Summary

• Preserve engine-aware row-prefix slicing so pandas does not scalarize whole-node reentry prefixes.
• Correlate hidden WITH-scalar carries through each surviving Polars edge step, including multi-edge paths and forward/reverse/undirected traversal.
• Exempt valid hidden reentry property access from destination-alias masking and fix Polars empty-prefix handling.
• Add pandas/Polars positive, empty-negative, multi-edge, multiplicity, no-reentry, and typed scalar coverage.
• Add direct cuDF convergent positive and partial edge-filter rejection coverage.

Closes #2252.

Validation

• Focused non-cuDF issue_2252 or issue_1413 or reentry selection: 141 passed.
• Focused cuDF-only local runtime guard: 1 skipped (cudaErrorNoDevice).
• DGX 26.02 exact-source focused cuDF test: admitted under 8 GiB RMM guard, then skipped. Diagnostic failed allocating 24 bytes (std::bad_alloc); contemporaneous foreign VLLM::EngineCore held 60,103 MiB. Recorded as unavailable, not parity or a product regression.
• Ruff: passed. Type-hygiene guard: 4,439 grandfathered findings, no growth. Comment guard: passed. Source-pinned repro: passed.
• Exact-head CI run: 40484557526, terminal SUCCESS. CodeQL run: 40484557483, terminal SUCCESS. RTD commit status: SUCCESS.

Identity

• Base: d53fba85532949fd8881d6cb8079ebbdf17cb111
• Head: cb2f6e0d0f9509c677f2b1fd8e6731fb5de980e3
• Tree: 0280263441ea48e18cfb869a807fc84025b946b1
• DGX receipt: plans/gfql-mcp-quality-2026-10-22/worker/receipts/p0705-dgx-cudf-cb2f6e0d0.md