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Have there been writings on what exactly git's migration strategy to a new hash function will be? Apparently they have a seamless transition designed that won't require anyone to update their repositories, which seems like a pretty crazy promise in the absence of details.

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In git the SHA-1 hash is simply an identifier for an object - it's used in the filename, but not stored in the object. And when a commit or tree object references others, it's just a name that can be looked up in the database. So a commit object hashed with SHA-256 can easily reference a previous commit that was hashed with SHA-1.

During the switch, a bit of deduplication may be lost. But the only interesting issue I can see is how git fsck will tell which hash an object was created with when verifying the hash (maybe with length?).

Git update repo kind of command may be ??

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