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GLOBAL+50 XP

Implement a Convergent PN-Counter CRDT Engine

Landmark Capstone: State-Based PN-Counter CRDT

In multi-leader distributed clusters and offline-first edge applications, nodes accept increments and decrements concurrently without centralized locking.

Your objective is to build a mathematically formal Positive-Negative Counter (PN-Counter) CRDT supporting independent updates and convergent join-semilattice merges.

Requirements:

  1. Local Vector Operations: Each node maintains independent positive (P) and negative (N) increment maps keyed by nodeId.
  2. Scalar Computation: The counter value must always equal sum(P) - sum(N).
  3. Join-Semilattice Merge Function: When merging remote state, calculate the element-wise maximum for each node key (P_merged[k] = max(P_local[k], P_remote[k])).
  4. Mathematical Properties: The merge operation must strictly satisfy Commutativity, Associativity, and Idempotence.

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