phase: generate a push-race detection part on push We are about to switch phase pushing from using pushkey to using a the new dedicated binary part. We introduce the push race detection on its own to help detect potential impact.

phase: introduce a new 'check:phases' part This part checks if revisions are still in the same phase as when the bundle was generated. This is similar to what 'check:heads' or 'check:updated-heads' bundle2 part achieves for changesets. We needs seems before we can move away from pushkey usage from phase since pushkey has it own built-in push-race detection.

phase: gather remote phase information in a summary object We keep useful phase information around. The data will be reused with detecting push-race in later changesets.