Potential leak in v17 (bank) and v18 (smart wallet)

[arirubinstein]

on agoric-3, it appears that v17 and v18 are growing in size over time:

[dckc]

It's less surprising that vat-bank grows; #5885 is still open.

#4489 is closed, so the smart wallet should be using virtual objects to limit heap growth.

[dckc]

@mhofman pointed out that this closure likely keeps all representatives in the heap rather than just in virtual storage:

agoric-sdk/packages/smart-wallet/src/smartWallet.js

Lines 523 to 524 in 2c812d2

	// watch the bank for new issuers to make purses out of
	void observeIteration(E(bank).getAssetSubscription(), {

[turadg]

I think @dckc fixed this in #6774. There's only one observer, within the asset registry shared by all wallets:
https://github.com/Agoric/agoric-sdk/blame/9aa48736a3b158f8e8746e815f7a94887e02b46e/packages/smart-wallet/src/walletFactory.js#L64-L78