[Bug]: Fix Permit token decimal amounts

[digiwand]

Describe the bug

If no contract was found within the Permit DataTree component, we should use the verifiedContract tokenDecimals. Passing the verifiedContract's tokenDecimals, when no decimals are found for this contract, will apply the default 18 token decimals. This is missing. Notice in the screenshot that Spending Cap displays "< 0.000001", while Message > Value displays "3,000". Value should also display "< 0.000001".

Details of applying default 18 token decimals to Redesigned Permit

When we adopted fetchErc20Decimals for Permit Simulation, we enforced a default of 18 token decimals to be used when no token decimals were found in the details. fetchErc20Decimals is the same method used in ui/pages/confirmations/components/simulation-details/useBalanceChanges.test.ts which is why we adopted it.

Previously, clicking on test-dapp > Permit would display 3,000. Now, it displays 0 < 0.000001.

@dbrans:

18 is the common convention for ERC20 tokens, largely due to OpenZeppelin's widely-used implementation. Vitalik proposed making it a required standard, though it didn’t gain momentum. EIP-1046 also suggests 18 as the default if decimals() isn’t implemented.

That said, some platforms, like Etherscan and certain wallets, default to zero when decimals() isn't defined, so there's a lot of inconsistency out there.

Expected behavior

No response

Screenshots/Recordings

Notice that Simulation > Spending Cap value does not match Message > Value

Steps to reproduce

1. Go to test-dapp
2. Click Permit button
3. Observe Spending Cap and Message > Value

Error messages or log output

No response

Detection stage

On the development branch

Version

12.2.2

Build type

None

Browser

Chrome

Operating system

MacOS

Hardware wallet

No response

Additional context

No response

Severity

No response

[bschorchit]

As discussed in the DSU, we can adopt the 18 decimals as the fallback and add metrics to capture when we fail to fetch decimals.
For metrics, we can re-use this event that we created for simulations:

event: Incomplete Asset Displayed

properties:
token_decimals_available: false
asset_address: < token address >
asset_type: erc20
chain_id: < chain id >
location: confirmation

[digiwand]

thank you @bschorchit! I created a separate ticket for this one: #27333