fix(rpc): cap eth_getLogs filter addresses and topics

[crazywriter1]

Problem

eth_getLogs is unauthenticated and accepts unbounded address and per-slot topics vectors. Each address triggers a separate index lookup the EL resolves per matched block, and each topic entry multiplies the per-block work. A single malicious request with thousands of entries can monopolize the executor thread the EL also uses for the engine API, with the potential to cascade into missed sequencer block production windows.

This is the same DoS class as the eth_getProof storage-key vector capped in #2596 (MAX_PROOF_KEYS = 1024).

Fix

Reject filters that exceed parameter-level caps before any DB access:

• MAX_LOG_ADDRESSES = 1000
• MAX_LOG_TOPICS_PER_SLOT = 1000 (applied to each of the 4 topic slots)

Legitimate dApp traffic — typically a handful of contracts and a few topic values — is unaffected. Block-range capping is handled separately by reth's filter settings and is intentionally out of scope here.

Files

• crates/execution/flashblocks/src/rpc/log_filter_limit.rs (new) — LogFilterLimit::check() + 5 unit tests
• crates/execution/flashblocks/src/rpc/mod.rs — module registration
• crates/execution/flashblocks/src/rpc/eth.rs — call LogFilterLimit::check(&filter)? at the top of get_logs

Tests

• accepts_empty_filter
• accepts_at_address_limit / rejects_above_address_limit
• accepts_at_topic_limit_in_each_slot / rejects_above_topic_limit_in_each_slot (all 4 slots)

All existing flashblocks integration get_logs tests (test_get_logs_pending, test_get_logs_filter_by_address, test_get_logs_topic_filtering, …) continue to pass — they use single-address / single-topic filters far below the cap.

Pattern reference

Follows the parameter-validation pattern established in #2596 (ProofKeyLimit) and matches go-ethereum's defense against pathological RPC inputs.

[cb-heimdall]

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