Define deterministic functional-profile lane choice for indexed memory

[zhoubot]

Architecture gap

Functional-model bring-up found two remaining E_Arbitrary nodes in the owning ASL: scatter commit ordering and MGATHER_CAS lane ordering. Portable PTO already permits any legal enabled-lane permutation, but an executable profile needs a named deterministic binding for reproducible oracle/library comparison.

Baseline

• PTO baseline: 0c1aa4ede00f9ef3ada881f37251c55a4b70fed7
• Affected owners: PTO-TILE-MODEL-MEMORY-GATHER-SCATTER, PTO-TILE-MODEL-MEMORY-ATOMICS, PTO-ARCH-PROFILE-REFERENCE-PROFILE
• New clause: PTO-REQ-INDEXED-MEMORY-LANE-CHOICE-001

Proposed contract

• Portable semantics retain an implementation-defined legal permutation; no row-major order becomes portable.
• Every enabled lane appears exactly once and each selection names a not-yet-committed lane.
• The pto-v0 reference/generated functional profile binds policy pto-v0-indexed-memory-logical-ascending-v1.
• Target profiles may bind a different legal permutation only under a distinct profile identity and executable evidence.
• Selection itself has no architecture-visible state or fault effect.

Focused evidence

• pure/profile choice legality and boundary points
• duplicate-address MSCATTER and MGATHER_CAS reference-order points
• typed AST E_Arbitrary count becomes zero
• ASLRef/generated differential remains exact

Release impact

Required for PTO ISA 0.58.5 functional-model generation; encoding and assembly are unchanged.