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Gut the "outer" Create() and move it to the inner BeginCreate(). This
uses a "transaction" type to make cleanup functions easy to read.
Background:
Service has an "outer" and "inner" REST handler. This is because of how we do IP and port allocations synchronously, but since we don't have API transactions, we need to roll those back in case of a failure. Both layers use the same `Strategy`, but the outer calls into the inner, which causes a lot of complexity in the code (including an open-coded partial reimplementation of a date-unknown snapshot of the generic REST code) and results in `Prepare` and `Validate` hooks being called twice.
The "normal" REST flow seems to be:
```
mutating webhooks
generic REST store Create {
cleanup = BeginCreate
BeforeCreate {
strategy.PrepareForCreate {
dropDisabledFields
}
strategy.Validate
strategy.Canonicalize
}
createValidation (validating webhooks)
storage Create
cleanup
AfterCreate
Decorator
}
```
Service (before this commit) does:
```
mutating webhooks
svc custom Create {
BeforeCreate {
strategy.PrepareForCreate {
dropDisabledFields
}
strategy.Validate
strategy.Canonicalize
}
Allocations
inner (generic) Create {
cleanup = BeginCreate
BeforeCreate {
strategy.PrepareForCreate {
dropDisabledFields
}
strategy.Validate
strategy.Canonicalize
}
createValidation (validating webhooks)
storage Create
cleanup
AfterCreate
Decorator
}
}
```
After this commit:
```
mutating webhooks
generic REST store Create {
cleanup = BeginCreate
Allocations
BeforeCreate {
strategy.PrepareForCreate {
dropDisabledFields
}
strategy.Validate
strategy.Canonicalize
}
createValidation (validating webhooks)
storage Create
cleanup
AfterCreate
Rollback allocations on error
Decorator
}
```
This same fix pattern will be applied to Delete and Update in subsequent
commits.