(tree) Add versioning to shared tree and its summarizables' summaries #25876
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The summaries written by Shared Tree and its summarizables are not versioned. Any changes to the summary format can lead to failures in clients that do not understand this new format. For example, the incremental summarization feature changes the forest's summary format by adding more nodes to its summary tree which older clients won't be able to read. Making this change behind a new version makes it safer as we can fail fast on seeing unrecognizable versions.
This change adds versioning by adding a metadata blob to the summary tree of the shared tree and its summarizables. This metadata blob will contain the format version of the summary. Every time, the format of the summary changes, a new version should be added so that clients that don't understand this format will fail.
The metadata blob will be written when
minVersionForCollabis greater than the next release version 2.73.0.Since the metadata blob and hence the versions did not exist before 2.73.0, changes to the summary format will not result in failing them during reading from the snapshot. Instead, the faiilures may manifest later when the underlying data is read. So, the recommended way to change format is to do it in a way that will break as soon as possible. For example, chaging the id of the summary node where the summary is stored will result in older clients not finding the snapshot.
AB#53723