Need zone to abstract over watchPromise or vowTools

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At

agoric-sdk/packages/async-flow/test/test-async-flow.js

Line 61 in 1718b06

const testFirstPlay = async (t, zone, vowTools) => {

I found I had to pass in the vowTools to the test cases that should work across zones because

• the prepareVowTools from @agoric/vow works with the heap and virtual zones, but not the durable zone, and therefore does not support recovery from upgrade.
• the prepareVowTools from @agoric/vat-data/vow.js works with the durable zone and supports recovery from upgrade, but does not work with the heap or virtual zones.

I raised the with @michaelfig and, IIRC, we agreed that

• the underlying problem was the difference between the watchPromise exported by liveSlots (supporting durability and upgrade) vs the watchPromiseShim in @agoric/vow intended for cases where the "real" watchPromise is not available
• it might be reasonable to extend the Zone type to provide a watchPromise method that works with that zone. Then, code like the test cases in test-async-flow.js need only be parameterized over zone, and no longer additionally parameterized over vowTools.

This would address the issues @mhofman raises at #9097 (comment)

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See also #9097 (comment)

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@michaelfig , ok to assign this to the two of us?