Forks a new branch anchored at a retained commit version of the source branch, giving time-travel semantics: the new branch sees exactly the data visible at that version. A version outside retained history fails with history_unavailable.engine.persistence_history.

This command has no dedicated CLI verb: the CLI expresses it as strata branch fork <SOURCE> <BRANCH> --version <VERSION> (one shared branch fork verb routes to all three fork commands, so only branch.fork owns the CLI path). It remains fully reachable through the generic wire surface — strata command run, MCP, and SDKs.

Successful mutations return an acknowledgement that identifies the affected target, the mutation effect, and commit facts when the operation changed stored state.

Examples

Fork a branch at an earlier commit version — a snapshot of history.

CLI

$ strata kv put greeting original  # The receipt carries this commit's version.
$ strata kv put greeting updated
$ strata command run --command-json '{"branch":"snapshot","source":"default","type":"branch_fork_at_version","version":3}'  # snapshot forks default's history at that version.
$ strata kv get greeting --branch snapshot

Wire

{"key":"Z3JlZXRpbmc=","type":"kv_put","value":"b3JpZ2luYWw="}
{"key":"Z3JlZXRpbmc=","type":"kv_put","value":"dXBkYXRlZA=="}
{"branch":"snapshot","source":"default","type":"branch_fork_at_version","version":3}
{"branch":"snapshot","key":"Z3JlZXRpbmc=","type":"kv_get"}

Parameters

Name	Type	Required	Description
source	string	yes	Source branch name.
version	integer	yes	Source version.

Plus the optional scope: branch and space (default to the session branch and the "default" space).

Returns

MutationAck<BranchItem>.

Errors

• failed_precondition.engine.runtime_closed
• not_found.engine.branch
• invalid_argument.engine.branch_name
• invalid_argument.engine.branch_name_reserved
• already_exists.engine.branch
• history_unavailable.engine.persistence_history

Invocation

• CLI: via strata command run (no dedicated verb)
• Wire type: branch_fork_at_version