Let a module declare a stream of its own and restrict who hears it by a trusted config value (hq issue 718, ADR 0363)

mesh-mail's events must live on a stream of their own and reach only the modules the operator granted
an account (ADR 0359 §2, §4). The controller now creates a module's declared stream, publishes its events
on mesh.stream.<module>.event.<event>, and composes a consumer's durable consumer, filters and bus grants
on a restricted stream only where its consumes asks and the provider's trusted value names it; a consumer
that loses its grant has its consumer removed on the next assertion. Nothing changes while no manifest
declares a stream.

internal/broker/users.go

@@ -40,6 +40,13 @@ type Declared struct {
 	State []Bucket
 	// Logs are the logs it keeps, each a stream its instances append to (novox/hq ADR 0297).
 	Logs []Log
+	// Streams are the streams it owns, each its events' one place (novox/hq ADR 0363).
+	Streams []ModuleStream
+	// Hears are the module streams it hears on this machine, each with the subjects it was granted
+	// (novox/hq ADR 0363 §5); HearsAStream says its `consumes` names a module that owns a stream, granted
+	// or not, so its membership is issued again when a grant changes.
+	Hears        []Heard
+	HearsAStream bool
 	// Reads are other modules' state it reads, each `<module>.<name>` (novox/hq ADR 0201).
 	Reads []string
 	// KeyedReads are keys of other modules' state it reads, each one key alone: what a seat's holder is
@@ -129,7 +136,7 @@ func Users(r Records) ([]Principal, error) {
 				Holds: d.Holds, Uses: d.Uses, Watches: d.Watches, Invokes: d.Invokes,
 				State: stateNames(d.State), Reads: d.Reads, SnapshotsTheBus: d.SnapshotsTheBus,
 				PerMachine: perMachineNames(d.State), KeyedReads: d.KeyedReads,
-				Logs: logNames(d.Logs),
+				Logs: logNames(d.Logs), Streams: d.Streams, Hears: d.Hears,
 			})
 		}
 		if runtimeHere {