bootstrap upgrade complicated by 5 non-durable exports

[dckc]

Describe the bug

The bootstrap vat has 5 non-durable objects. So upgrading it will sever those exports; in particular, the coreEval handler, provisioningHandler, and prioritySenders manager.

To Reproduce

agoric-sdk/packages/boot/test/bootstrapTests/test-vaults-upgrade.ts

Lines 158 to 170 in 7386420

	test.serial('audit bootstrap exports', async t => {
	const expected = {
	maxExports: 5,
	maxNonDurable: 5,
	ifaces: {
	// in bridgeCoreEval()
	coreHandler: true,
	// in bridgeProvisioner()
	provisioningHandler: true,
	'prioritySenders manager': true,
	// TODO? move to provisioning vat?
	clientCreator: true,
	},

Expected behavior

A clear and concise description of what you expected to happen.

Platform Environment

all platforms since mainnet1B launch.

Additional context

This issue is mainly to provide back-pointers to work that it impacts.