messagequeue

type Message struct {
	// ID uniquely identifies the message for deduplication and tracing.
	//
	// Deduplication is against every message the backend still holds for the
	// same topic and partition key — including ones already consumed, which are
	// reclaimed lazily and may outlive their delivery by an unbounded interval.
	// A publish whose ID collides is reported as a success and stores nothing.
	//
	// So the ID names the occasion to publish, not the entity published about.
	// Reusing an entity's own ID gives that entity one message for as long as
	// the backend remembers the first, and silently discards every later one.
	// Producers build IDs with platform/publish.IntentID rather than choosing
	// them by hand.
	ID string

	// Payload is the message body as raw bytes.
	Payload []byte

	// Metadata contains key-value pairs for headers and attributes.
	// Use for trace IDs, request IDs, and cross-service metadata.
	Metadata map[string]string

	// PartitionKey determines which partition/shard this message goes to.
	// Messages with the same PartitionKey are guaranteed ordered delivery.
	// Optional - if empty, backend may use round-robin distribution.
	PartitionKey string

	// PublishedAt is when the message was published (Unix milliseconds).
	PublishedAt int64
}