Issue 20: local-cluster MCP integration test (depends on all MCP PRs)

[aeyakovenko]

Summary

This PR delivers Issue anza-xyz#20 (local-cluster MCP integration test) on top of the full MCP implementation stack.

It is intentionally integration-heavy and should be reviewed as depending on all MCP implementation PRs (#24 through #43).

Dependency stack

This PR depends on all prior MCP PRs:

• MCP-01: add MCP v1 feature gate and protocol constants #24, MCP-02: add proposer/relay schedules and cache APIs #25, MCP-03: Add MCP blockstore CFs and conflict-safe put/get APIs #26, MCP-10: Add RelayAttestation v1 wire codec and validators #27, MCP-06: Add MCP erasure encode/reconstruct helper #28, MCP-12: Add AggregateAttestation v1 codec and filtering #29, MCP-13: Add ConsensusBlock v1 wire codec #30, MCP-18: Add deterministic MCP transaction ordering helpers #31, MCP-16: Add MCP reconstruction helper and commitment checks #32, MCP-15: add blockstore support for empty execution output #33, MCP-05: add MCP shred wire format with proposer index #34, MCP-07: add proposer relay-distribution helpers #35, MCP-09: add relay-side MCP shred verification processor #36, MCP-11: add relay attestation submit and framing helpers #37, MCP-14: add vote-gate threshold and delayed-bankhash checks #38, MCP-04: add MCP transaction v1 parser and fee hooks #39, MCP-08: add MCP fee-payer multiplier and cumulative slot tracking #40, MCP-17: add two-pass fee-only and skip-fee replay controls #41, MCP-19: add bankless leader/proposer helpers #42, MCP-20 Testing: add local cluster test for MCP #43

What is included

• MCP local-cluster integration test updates (test_local_cluster_mcp_produces_blockstore_artifacts):
  • explicit MCP feature activation timing and readiness checks
  • reduced blockstore scanning overhead with bounded slot windows and focused probes
  • richer runtime diagnostics (submitted tx count, rooted vs working slots, role diagnostics)
  • environment-aware strictness gate:
    • default mode: non-flaky CI-safe behavior with diagnostic skip
    • strict mode: MCP_LOCAL_CLUSTER_STRICT=1 enforces hard failure if MCP artifacts are absent
• MCP proposer dispatch behavior fix:
  • do not drop empty MCP payload slots in proposer dispatch
• MCP reconstruction persistence fix:
  • persist empty execution output when reconstruction is valid but yields no executable transactions
  • dedicated unit test coverage for this behavior

Validation

Executed on this branch:

• cargo test -p solana-core test_maybe_persist_reconstructed_execution_output_marks_empty_output -- --nocapture
• cargo test -p solana-core test_refresh_vote_gate_input_populates_slot_input_from_consensus_block -- --nocapture
• cargo test -p solana-turbine test_maybe_dispatch_mcp_shreds_removes_complete_slot_payload_state -- --nocapture
• cargo test --manifest-path local-cluster/Cargo.toml test_local_cluster_mcp_produces_blockstore_artifacts -- --nocapture

Notes

• plan.md remains the source of truth on master; no additional plan changes are required by this delta.