Overlay v2 mempool fix

[SirTyson]

Description

Fixes various mempool bugs.

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document

[tacticalnoot]

Superseded by the consolidated hardening handoff below: #5446 (comment)

Preserved evidence: dropped speculative transport state must not make valid demand permanently unavailable.

[tacticalnoot]

Superseded by the consolidated hardening handoff below: #5446 (comment)

The earlier admission/eviction case remains useful evidence; the current cross-phase allocation result is the broader surviving invariant.

[tacticalnoot]

Tyler — the classic/Soroban split is a real improvement; the hardening pass found one allocation edge that still survives exact head ef563837….

Issue: phase-local nomination is still backed by one shared eviction authority. At capacity, evict_lowest_fee() selects a victim across both phase indexes, so pressure from one phase can erase the other phase’s residency before Core ever queries it.

Proof: the exact-source 601 witness starts with equal Classic/Soroban residency and valid one-phase pressure drives the other phase to zero. Later GetTopTxs(kind, …) cannot restore entries already evicted.

Move: make cross-phase capacity allocation explicit and Core-owned (floor/budget/borrow-reclaim or another deterministic rule — not prescribing quotas).

Would you be up for a tiny regression that fills both phases, pressures one, and requires the other phase’s intended availability invariant to survive?

[SURUJ404]

can promote TX adverts demands to scp stream TX_DEMAND_VECTOR_MAX_SIZE fixed the multipleFloodDemabd messages