Data Flow

This page keeps only the cross-capability view. Each authoritative capability page owns its complete sequence, state machine, and procedures.

Overview

Capability Handoffs

Handoff	Upstream delivers	Downstream owns	Authoritative pages
Command ingress	Command payload, target aggregate, request identity, and wait target	Validate and send a CommandMessage	Define Commands, Send Commands
Aggregate decision	Current sourced state and a command	Check invariants and produce domain events	Aggregate and Invariants, Aggregate Lifecycle
Authoritative history	Ordered DomainEventStream	Append under version constraints and support restoration	Event Sourcing
Event collaboration	Persisted domain events and state events	Dispatch to Processors, Sagas, Projections, and Snapshots	Event Dispatch Pipeline, Events and Collaboration
Derived processing	Matching event-function invocation	Complete a side effect, later command, projection, or snapshot	Event Processor, Saga, Snapshots
Caller observation	Stage signals from each processing chain	Select the earliest sufficient stage and handle unknown outcomes	Completion Semantics, Failures and Idempotency

A failure after EventStore append cannot roll back committed history. Transport redelivery, idempotency, event compensation, or replay owns later recovery; see Event Dispatch Pipeline and Event Compensation for the exact boundaries.

Read Paths

Aggregate-state reads and projection reads have different purposes:

• aggregate restoration reads snapshots plus EventStore for the next business decision;
• query APIs read projections, snapshots, or another query store for users.

A projection may still be stale immediately after PROCESSED. Target the exact PROJECTED function to observe completion of its returned reactive chain instead of sleeping for a fixed interval, then execute the actual query to prove visibility. Work outside that chain, caches, replicas, and unrelated query pipelines remain separate evidence. See Projection and Query.

Cross-Capability Failure Location

Observation	Enter the authoritative page
No SENT	Send Commands and Command Transport
SENT but no PROCESSED	Command Processing Pipeline and Failures and Idempotency
PROCESSED but no SNAPSHOT	Snapshots and Event Dispatch Pipeline
PROCESSED but no downstream function stage	Events and Collaboration and Event Compensation
Wait timeout followed by changed state	Completion Semantics and Failures and Idempotency

See Troubleshooting for production diagnosis and Observability for metric and trace mapping.