event-gate erc20 balance reads

[mrq1911]

Problem

BalanceClient.watchErc20Balance is the #1 per-block RPC cost of an active sdk-next context. Today it does:

this.watcher.bestBlock$.pipe(switchMap(() => fetchBalance(ids)))

→ re-reads every ERC20 id via CurrenciesApi.account (a chainHead_v1_call) on every block, unconditionally. The distinctUntilChanged only suppresses emissions, not the RPC ops. Measured on a mainnet chainHead node (Treasury account, 64 pools / 43 ERC20 slots): ~84 chainHead_v1_call/block, all CurrenciesApi_account.

Fix (event-gated)

• Seed once with a full read (unchanged first-block behaviour).
• Subscribe to EVM.Log.watch(), decode ERC20 Transfer(from,to,value) logs, map the emitting contract → asset id via the existing ERC20.toAssetId (structural 0x..01<id> precompile prefix — no RPC; same mapping AavePoolClient uses in reverse).
• Re-read only the (address, id) pairs where the watched account is from/to (account compared via H160.fromAny).
• Safety net: full re-read every N=20 blocks so a missed/unmapped log (e.g. a non-EVM mutation of an ERC20-typed asset) can't permanently stale a balance.
• A running snapshot map keeps every emission the complete ERC20 balance set, preserving the previous output shape.

Public watchErc20Balance / watchBalance signatures are unchanged (internal only).

Benchmark (mainnet chainHead, same harness, only the lib changes)

CurrenciesApi_account calls per block, Treasury account, 64 pools / 43 ERC20 slots:

	CurrenciesApi_account/block	total chainHead_v1_call/block	storage ops/block
master	84	84	~162
this PR	0 (idle)	0.43	~166

Idle blocks drop to 0 CurrenciesApi_account calls; the residual 0.43 is the unrelated router Aave-executor call from the spot-price loop. Storage ops unchanged → the change targets exactly the ERC20 call fan-out and nothing else.

Regression

• Existing suite green: 16 suites / 67 tests pass (baseline 15/57; +1 suite / +10 from the new Erc20Log.spec.ts).
• Functional equivalence (verified): read every ERC20 balance for the account at the same pinned block on master vs this branch → byte-identical for all 23 ids, 0 mismatches. (The read path getBalanceData → CurrenciesApi.account is untouched; only the scheduling changed.)
• Balance still updates on activity (verified by decode test + reasoned): the Erc20Log decoder + the from/to gate are unit-tested against synthetic Transfer logs (sender match, receiver match, wrong-asset drop, unrelated-account drop, non-asset-contract → null). A real Transfer touching the account triggers a targeted re-read; the safety re-read backstops any missed log.

Notes

• New focused unit test: packages/sdk-next/src/client/Erc20Log.spec.ts (10 cases) covering the pure decoder + the event-gate predicate.
• Changeset added (sdk-next patch).

[changeset-bot]

🦋 Changeset detected

Latest commit: e0bca73

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@galacticcouncil/sdk-next	Patch

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