Add atomic keyed rebuild publication

[PraneethMerugu]

Adds the implementation-demonstrated C09 rebuild policy to the existing KeyedReduce/KernelAbstractions path. Rebuilds ignore stage-entry records, seed emitted keys from an exact identity, preserve canonical fold order, and replace count plus records only after successful validation; incremental NewKeyIdentity behavior is unchanged. Capacity and prior-state inclusion remain runtime data, with no Potts vocabulary, scheduler, storage authority, second executor, or model-graph specialization.

Qualification at 9d5b383:

• complete CPU package suite: 1,869/1,869
• focused real Metal with scalar indexing disabled: 37/37
• strict documentation build: pass
• independent review and re-review: clean after correcting a duplicate-emission prior-count bug
• exact C08-to-candidate code_typed/MethodInstance comparison: semantic boundaries and specialization counts unchanged; reset device body +4 statements/+1 call/+1 control-flow-only Any; host orchestration +1 statement/+1 call; allocations unchanged at 8,432 bytes for incremental and rebuild public execution
• Core R10 consumer: capacity-greater-than-emission duplicate pair-key fold passes on CPU and real Metal and matches its independent oracle

This is the narrow LocalMath prerequisite for Core R10/Potts R11 maintained relationship reconstruction. It does not claim those downstream PRs complete.