Include the declared gas fee in MAYAChain/THORChain fees

[j0ntz]

CHANGELOG

Does this branch warrant an entry to the CHANGELOG?

• Yes
• No

Dependencies

none

Description

Asana task

Asana: https://app.asana.com/1/9976422036640/project/1201386023359434/task/1214062657363212

A CACAO max send never left the wallet. The app reported "Transaction Success"
and wrote a sent transaction into history, but nothing moved on-chain.

MAYAChain and THORChain price a transaction by a flat network fee rather than by
gas, so MayachainEngine and ThorchainEngine quote that flat fee and declare a
token gas fee of 1 base unit. The signer pays BOTH: the ante handler collects the
declared gas fee before the message runs. Only the flat fee was reported as
networkFee, and since the cosmos plugin has no getMaxSpendable, edge-core-js
binary-searches makeSpend and checkBalances only enforces
amount + networkFee <= balance. A max send therefore landed on
balance - flatFee, whose real cost is balance + 1. The chain accepted it at
CheckTx and then reverted it in DeliverTx as insufficient funds.

The two engines now share a makeMidgardFee helper on MidgardEngine that owns
the declared gas coin and folds its amount into the reported networkFee.

Evidence the declared fee is a real deduction, from mayanode: every MsgSend's
first transfer event pays auth_info.fee.amount to the fee collector
maya17xpfvakm2amg962yls6f84z3kell8c5lkfyhgj, separate from the 2000000000
native-fee split (txs 78BA4DCE97C88FC72886DAC67FF67A8B1C22E83C85D38CF8718B51D491E34F77
and 128511AD8D479524A2E1F6C5C9DE77029AE2E5EAFA4F5A0F946385536F033E49).

Verification

Driven in the app on the iOS simulator with this branch baked in via updot,
sending between two CACAO wallets on edge-funds.

	before	after
MAX amount offered	10.15 CACAO	10.1499999998 CACAO
fee shown	0.2	0.2000000001
on-chain result	BFBC11AF… code 1, insufficient funds	544BA17E… code 0
sender balance	unchanged apart from the 1-unit gas fee	emptied to 0
recipient balance	unchanged	+101499999998 exactly

An ordinary non-max send was driven afterwards and also lands code 0
(051A9C29…),
with the sender debited amount + 2000000000 + 1.

test/cosmos/midgardCalculateFee.test.ts covers the fee arithmetic.
verify-repo.sh passes (install, prepare, eslint, mocha).

Notes for review

• THORChain is corrected by symmetry: its calculateFee has the same shape and
  the chain is what MAYAChain forked from. Its public nodes were unreachable from
  the machine this ran on, so RUNE was not exercised on-chain. The change is safe
  either way: if RUNE does not charge the declared fee, a max send merely leaves
  1 base unit (1e-8 RUNE) behind rather than failing.
• The Send scene now renders the fee as 0.2000000001 instead of 0.2, because
  the reported fee is the amount the chain actually takes. Rounding that back to
  a pretty 0.2 for display would reintroduce the failure if it were also used
  for the max calculation, so it is left accurate here.

---

Note

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[j0ntz]

📸 Test evidence

max amount and fee

tx success

postfix max amount and fee

postfix tx success

postfix txid detail

postfix wallet emptied

postfix normal send success

Captured by the agent's in-app test run (build-and-test).

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