Function derive_inverse_command 

pub fn derive_inverse_command(
    forward: &Command,
    step: &UnresolvedStep,
) -> Option<Command>

Map a forward Command to its compensating inverse, given the recorded step row (which carries the forward command’s emitted events in output_json, useful for Create* → extract-new-id → Delete*).

Returns None for commands whose inverse cannot be derived from the saga log alone (caller logs + skips). Documented limitations:

• MoveTab and MoveBlock: we don’t know the source’s dst_index the tab/block was originally at, so we can’t perfectly restore the prior order. We construct a swap that at least returns the tab/block to its source — index 0. This is incorrect for re-ordering inverses but acceptable for the common tear-off case (where the source workspace’s order is not the saga’s concern; the saga only cares the tab is back in src).
• Any Delete*: not invertible — un-deleting requires reconstructing the deleted entity’s full state, which is gone from the saga log by definition.
• Update*Meta, Rename*, SetActiveTab, etc: pure-state patches whose inverse needs the prior value. The saga log doesn’t capture pre-state today (deferred to a future spec bump).