KarpelesLab / libwallet / 24421574149

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Transaction:simulate — decoded preview per chain

New wlttx/simulate.go exposes `Transaction:simulate`, returning a
structured SimulationResult for the approval sheet. Covers:

EVM:
- eth_call on the current network; revert → willRevert + decoded
  Error(string) reason
- On success: eth_estimateGas → gasEstimate
- Calldata decoding: recognizes ERC-20 transfer / approve (common
  drainer patterns) and surfaces decodedMethod + typed decodedArgs
  (token, to / spender, amount). Unknown selectors fall back to
  {selector, data} so the host can still display something.
- Plain native transfer (no data, non-zero amount) → native_transfer.

Solana:
- Wraps simulateTransaction (commitment: processed, sigVerify: false)
- Returns program logs, unitsConsumed, and any error encoded as JSON
- Includes native_transfer decoding when amount is set.

Bitcoin-family:
- Parses tx.Raw via outscript.BtcTx.UnmarshalBinary
- Returns per-input (txid, vout) and per-output (amount, script hex)
- Fee surfaced when the tx was built by libwallet (tx.Fee already set).

Dart:
- TransactionSimulation model + BitcoinIO
- TransactionApi.simulate(UnsignedTransaction) → TransactionSimulation
- Barrel export + integration test covering ERC-20 transfer calldata
  decoding (runs even when the RPC is unreachable in CI).

api.md entry added. 107 Dart tests pass.

v1 scope notes:
- ERC-721 / ERC-1155 decoding not implemented yet (follow-up).
- Bitcoin output addresses not resolved; raw script hex is surfaced
  instead (outscript doesn't expose a script→address decoder).
- Bitcoin input amounts require a per-input prev-txo RPC and aren't
  fetched in v1 — fee is instead taken from the known tx.Fee.

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

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