Cancel stale transactions

[rachelcope]

As a user, I want old or stale transactions to be canceled so that I don't have a buildup of transactions that are no longer relevant to me.

Automatically cancel transactions when:

1. A transactions is pending for over 12 hours
2. When a new transactions is initiated from a different dapp than any current pending transaction
3. When a user closes the MetaMask confirmation window

This is related to the design work for pending transactions: https://www.figma.com/file/hm2RQXkH2QVRJnnTnArLM7/Confirmations?node-id=656%3A1

And Reject all pending confirmations when notification window closed #10302
#10302

[danfinlay]

This is a challenging one to do safely, because even if a tx has been stale for a long time, miners could still be aware of it, and could mine it spontaneously, and so if we did this, we would still need to provide UI to educate the user about what happened when the "cancellation" failed, and the old TX got mined.

This applies to long queues of stale transactions too, making it even more complicated.

I do think there's some room for lower-hanging fruit, like "dismiss tx" as a button (with some educational info attached to it), so users don't have to "reset account" just to submit a tx with a reused nonce.

[danjm]

@danfinlay So you would say that this still needs design?