Keep what each machine says of what it runs, raise it, and gate on it (hq ADR 0240, to-be 48 Phase A)

The gate judged a module by what the mesh saw from outside, so a container that
crash-looped after it applied passed it. Each machine's node-engine now states
the health of every long-running resource it runs; the controller keeps the
newest statement per machine, raises module.<module>.<machine>.unhealthy on the
second statement in a row, clears it on the first that does not say it, and the
gate passes a module only when every long-running resource of it is stated
healthy since the send. An engine that states nothing is judged as before.

internal/link/protocol.go

@@ -262,6 +262,13 @@ type Report struct {
 	// `witness` and `not-reversible` are sent only to a machine whose report carries it.
 	Witness int `json:"witness,omitempty"`
 
+	// Health is the machine's word on every long-running resource it runs for a module (novox/hq ADR
+	// 0240, to-be 48 §4; mesh-host's internal/liveness): its state, since when, its failing streak and
+	// the restarts its node-engine counted. **Absent from an engine older than the judging**, which is
+	// read as "not known" — never as healthy, never as a reason to raise anything; present with no
+	// resources from a machine that runs nothing long-lived.
+	Health *Health `json:"health,omitempty"`
+
 	// Rekey is a node taking a found tunnel's key as its overlay key after enrolment (novox/hq
 	// ADR 0105). A report carrying one is not an account of the machine: it moves the node's
 	// overlay key and tunnel and nothing else.
@@ -404,3 +411,45 @@ func EnrolProof(secret string, public []byte, overlay, sealing, serving string)
 	return []byte("novox-mesh-enrol\x00" + secret + "\x00" + base64.StdEncoding.EncodeToString(public) +
 		"\x00" + overlay + "\x00" + sealing + "\x00" + serving)
 }
+
+// LivenessContract is the version of the health statement this controller reads (ADR 0240 Phase A).
+const LivenessContract = 1
+
+// Health is one statement of a machine's long-running resources (to-be 48 §4): in every report, as the
+// event HealthSubject between reports on each change, and again every minute while one is not healthy.
+// The node-engine's own (mesh-host internal/link Health); a test on each side holds the field names.
+type Health struct {
+	Contract int `json:"contract"`
+	// At is when the engine looked, on the machine's clock: the order of its statements.
+	At        time.Time        `json:"at"`
+	Resources []ResourceHealth `json:"resources"`
+}
+
+// The states a resource is said in (ADR 0240 §4).
+const (
+	StateHealthy   = "healthy"
+	StateUnhealthy = "unhealthy"
+	StateStarting  = "starting"
+	StateHeld      = "held"
+	StateUnknown   = "unknown"
+)
+
+// ResourceHealth is one long-running resource's state.
+type ResourceHealth struct {
+	Module   string    `json:"module"`
+	Resource string    `json:"resource"`
+	Kind     string    `json:"kind"`
+	Target   string    `json:"target"`
+	State    string    `json:"state"`
+	Reason   string    `json:"reason,omitempty"`
+	Since    time.Time `json:"since"`
+	Streak   int       `json:"streak,omitempty"`
+	Restarts int       `json:"restarts,omitempty"`
+}
+
+// HealthSaid is the health event's body: the machine and its statement. The machine is read from the
+// subject the bus let it publish on, never from here.
+type HealthSaid struct {
+	Node   string `json:"node"`
+	Health Health `json:"health"`
+}