CommandBook

A collection of commands to be sent to aggregates. The CommandBook is the output of sagas and process managers.

Structure

message CommandBook {
  Cover cover = 1;           // Target aggregate identity
  repeated CommandPage pages = 2;  // Commands to execute
  SagaCommandOrigin saga_origin = 3;  // For compensation tracking
}

CommandPage

Each page contains:

Command payload: The actual command (Any type)
Sequence: Expected aggregate sequence (for concurrency)
Merge strategy: How to handle conflicts

Merge Strategies

Strategy	Behavior
`MERGE_STRICT`	Reject on sequence mismatch
`MERGE_COMMUTATIVE`	Allow if mutations don’t overlap
`MERGE_AGGREGATE_HANDLES`	Aggregate decides
`MERGE_MANUAL`	Route to DLQ for review

Saga Origin

Tracks the source of saga-issued commands for compensation:

Saga name
Triggering aggregate (domain, root)
Triggering event sequence

If the command is rejected, a RejectionNotification is sent back to the saga.