KarpelesLab / libwallet / 24422014076

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simulate: use erigon debug_traceCall for depth-N transfer extraction

The previous EVM simulator only ran eth_call + eth_estimateGas and
decoded the top-level calldata. That misses the anti-drainer signal:
a dApp can send innocuous-looking calldata (e.g. increaseAllowance
for a tiny amount) that triggers a massive Transfer via a nested
call, and the user wouldn't see it.

Erigon v3 exposes debug_traceCall with the callTracer. Upgrade:

- Primary path: debug_traceCall(call, "latest", {tracer:"callTracer",
  tracerConfig:{withLog:true}}) → walk the full call frame tree,
  pull out every ERC-20 Transfer + Approval event and every
  value-carrying CALL/CREATE. Populates a new SimulationResult.Effects
  list — one Effect per transfer the tx will actually cause.

- Gas estimate comes from the root frame's gasUsed (no separate
  eth_estimateGas round trip).

- Revert reason decoded from the callTracer's revertReason field
  (standard Error(string) ABI) rather than parsed from the
  eth_call error string.

- Second pass: debug_traceCall(... {tracer:"prestateTracer",
  tracerConfig:{diffMode:true}}) → native-balance deltas for every
  touched address. Populates SimulationResult.BalanceChanges as
  signed decimal wei. Negative = net spend (includes gas cost).

- Fallback chain preserved: if the node doesn't expose debug_*,
  fall back to plain eth_call + eth_estimateGas and synthesize a
  single Effect from the top-level decoded call.

Dart:
- TransactionSimulation.effects (List<Effect>) and balanceChanges
  (List<BalanceChange>) exposed + exported.
- Effect has isNative / isErc20Transfer / isErc20Approve getters.
- BalanceChange has an isLoss convenience.

107 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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