feat(p2p): tx validation cache

[fcarreiro]

Overview

Adds a tx validation cache to the p2p layer so that repeated validation of the same transaction by the same validator reuses the prior result instead of redoing the work (notably the expensive proof verification).

Downside: Using this cache for validations adds up to 7ms overhead for each validation, when the object needs to be hashed. This is actually entirely (+90%) dominated by .toBuffer() time.

Cached validation is added for on-demand tx collection, but NOT for gossip and RPC ingress.

Changes

Cache core (p2p/src/msg_validators/tx_validator/)

• TxValidationCache — bounded, LRU-evicting cache keyed by (validatorSymbol, txHash). Stores the in-flight promise before awaiting, so concurrent validations of the same tx coalesce into a single call. get/set/delete take the cache key directly; key(validatorSymbol, tx) builds it.
• CachedTxValidator — wraps any TxValidator to route validateTx through the cache using the validator's identifier symbol. DataTxValidator and TxProofValidator gained stable identifiers.
• factory.ts — threads an optional TxValidationCache through the gossip (first/second stage), block-proposal, on-demand, and RPC validator builders, wrapping the state-independent validators (DataTxValidator, TxProofValidator, and the minimum-integrity aggregate) in CachedTxValidator.

LRU map extracted to foundation (foundation/src/collection/lru_map.ts)

• The hand-rolled doubly-linked-list LRU bookkeeping was factored out of TxValidationCache into a generic LruMap<K, V>, mirroring the existing LruSet. TxValidationCache now composes an LruMap<string, Promise<TxValidationResult>>. Added LruMap unit tests.

Wiring

• New P2P_TX_VALIDATION_CACHE_SIZE env var / txValidationCacheSize config (cache disabled when 0).
• createP2PClient constructs the cache and passes it to LibP2PService (gossip + block-proposal paths) and to the batch-tx-requester's on-demand validator config.

Benchmarks

• Added a sha256-based TX hash benchmark.

Closes https://linear.app/aztec-labs/issue/A-934/dont-repeatedly-verify-retrieved-transactions .

[fcarreiro]

I can remove this one, otherwise there would be overhead for gossip as well

[fcarreiro]

Dropped these.

[PhilWindle]

This will of course keep up to maxSize complete transactions in memory. At ~100KB per tx and 5,000 default maxSize thats 500MB. I'm wondering whether this is a good trade off. We probably don't validate the same object very frequently if at all.

[fcarreiro]

Changed it to a WeakMap which has exactly the semantics we want and doesn't hold on to references. It's not an LRU though, so it will hold values for any TX that has been validated AND is still around. This is actually nice because the eviction will probably match mempool eviction or similar.

[AztecBot]

Flakey Tests

🤖 says: This CI run detected 1 tests that failed, but were tolerated due to a .test_patterns.yml entry.

\033FLAKED\033 (8;;http://ci.aztec-labs.com/6e078d4be689fa6d�6e078d4be689fa6d8;;�): yarn-project/kv-store/scripts/run_test.sh src/sqlite-opfs/internal/ordered-binary-browser.test.ts (2s) (code: 0)