[VSJoin-Exec] Mechanism II gap closure: budgeted boundary coverage routing

[ZeroJustMe]

Theme

Mechanism II: Budgeted Boundary Coverage Routing

Problem to close

Need a clear runnable contract across unicast, budgeted multicast, and broadcast with bounded fanout and dedup semantics.

Implementation Tasks

• Expose fanout budget and route mode in VSJoin strategy config.
• Implement/verify deterministic candidate selection under budget.
• Enforce output dedup before sink-visible emission.
• Add coverage-overhead metrics:
  • routed partitions per probe
  • duplicate candidates before dedup
  • recall/latency/cost deltas across fanout budgets

Validation

• Add mode sweep tests: unicast vs budgeted multicast vs broadcast.
• Include at least one degradation case where higher fanout hurts cost.
• Keep baseline semantics consistent under evaluated workloads.

Paper Follow-up (Ch3/Ch4/Ch5)

• Ch3: reframe as budgeted coverage optimization.
• Ch4: state exact dedup and budget semantics.
• Ch5: add recall-cost frontier evidence.

Acceptance Criteria

• Budget effect is measurable and reproducible in provided configs.