The profile names the network manager that is running, and travels in every report (hq ADR 0161)

One capability per manager — uplink-networkmanager, uplink-systemd-networkd, uplink-dhcpcd — from
systemctl is-active, so the uplink seat's holder for a manager this machine does not run is refused
the way any missing capability is, naming it (issue 138). The apply that reports detects the profile
again and sends it, the same shape enrolment sends, so a machine that switched managers reaches the
mesh at its next push.

cmd/mesh-host/main.go

@@ -818,10 +818,7 @@ func enrol(ctx context.Context, opts options) error {
 	// control plane cannot decide what a node should run without it, so it travels with the
 	// request instead of being asked for in a second round trip.
 	detected := profile.Detect(ctx, profile.Default(nil), opts.timeout)
-	reported := map[string]any{}
-	if raw, err := json.Marshal(detected); err == nil {
-		_ = json.Unmarshal(raw, &reported)
-	}
+	reported := profileAsReported(detected)
 
 	// Signed with the identity just generated, so the mesh can tell this machine from anyone else
 	// who knows its public key (novox/hq issue 083).
@@ -1418,7 +1415,8 @@ func applyAndKeep(ctx context.Context, opts options, raw []byte, signed *store.D
 		sched.Sync(declared, held)
 	}
 
-	report := link.Report{Carried: carriedPorts(updated), Declared: digestOf(raw), Host: runningVersion()}
+	report := link.Report{Carried: carriedPorts(updated), Declared: digestOf(raw), Host: runningVersion(),
+		Profile: profileAsReported(profile.Detect(ctx, profile.Default(nil), opts.timeout))}
 	// Which of this machine's links face outside, for the filter the mesh writes around them
 	// (novox/hq ADR 0140). Reported whatever the node's mode: a converged node's filter needs it,
 	// and an adopted one becomes converged without a further round trip. A machine that cannot read
@@ -1630,3 +1628,13 @@ func refuseOlder(kept store.Declared, keptErr error, sequence int64) error {
 	}
 	return nil
 }
+
+// profileAsReported is the profile as the mesh reads it — the same bytes enrolment sends, so a
+// report's profile and an enrolment's are one shape on the controller's side (novox/hq ADR 0161).
+func profileAsReported(detected profile.Profile) map[string]any {
+	reported := map[string]any{}
+	if raw, err := json.Marshal(detected); err == nil {
+		_ = json.Unmarshal(raw, &reported)
+	}
+	return reported
+}

internal/link/messages.go

@@ -110,6 +110,11 @@ type Report struct {
 	// and the mesh's up in its place, and where the found configuration's original was kept.
 	Tunnel *CarriedTunnel `json:"tunnel,omitempty"`
 
+	// Profile is what this machine can do, detected again by the apply that reports (novox/hq
+	// ADR 0161) — the same shape enrolment sends — so a capability gained or lost since enrolment,
+	// a network manager switched, reaches the mesh at the next push rather than never.
+	Profile map[string]any `json:"profile,omitempty"`
+
 	// Host is the version of the host that produced this report (novox/hq ADR 0141).
 	//
 	// Without it nothing can say a machine is behind, so "every machine current with its source"

internal/profile/detectors.go

@@ -20,6 +20,14 @@ const (
 	// state: whether one IS running. Assignment needs the first.
 	CapSeat       = "seat"
 	CapPrivileged = "privileged"
+
+	// The network manager this machine runs, one capability per dialect (novox/hq ADR 0161): the
+	// uplink seat's holder declares its own, so the holder for a manager the machine does not run
+	// is refused the way any missing capability is, naming it. Active, not installed — a machine
+	// may have two of these on disk and runs one.
+	CapUplinkNetworkManager  = "uplink-networkmanager"
+	CapUplinkSystemdNetworkd = "uplink-systemd-networkd"
+	CapUplinkDhcpcd          = "uplink-dhcpcd"
 )
 
 // commandCapability is the shape most detectors take: run something, and treat a working
@@ -202,6 +210,21 @@ func Default(runner Runner) []Detector {
 			why:    "asks the kernel for interfaces — needs the module, not just the tool",
 			runner: runner,
 		},
+		commandCapability{
+			name: CapUplinkNetworkManager, command: "systemctl", args: []string{"is-active", "NetworkManager.service"},
+			why:    "asks the init whether NetworkManager is running — the dialect the uplink seat's holder must speak",
+			runner: runner,
+		},
+		commandCapability{
+			name: CapUplinkSystemdNetworkd, command: "systemctl", args: []string{"is-active", "systemd-networkd.service"},
+			why:    "asks the init whether systemd-networkd is running — the dialect the uplink seat's holder must speak",
+			runner: runner,
+		},
+		commandCapability{
+			name: CapUplinkDhcpcd, command: "systemctl", args: []string{"is-active", "dhcpcd.service"},
+			why:    "asks the init whether dhcpcd is running — the dialect the uplink seat's holder must speak",
+			runner: runner,
+		},
 	}
 }
 

internal/profile/uplink_test.go

@@ -0,0 +1,39 @@
+package profile
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+// The uplink seat's holder must be the dialect the machine runs (novox/hq ADR 0161): the profile
+// names the network manager found active, one capability per manager, and nothing for one that is
+// merely installed.
+func TestTheProfileNamesTheNetworkManagerThatIsRunning(t *testing.T) {
+	runner := func(_ context.Context, name string, args ...string) (string, error) {
+		if name == "systemctl" && len(args) == 2 && args[0] == "is-active" {
+			if args[1] == "NetworkManager.service" {
+				return "active\n", nil
+			}
+			return "inactive\n", errors.New("exit status 3")
+		}
+		return "", errors.New("not here")
+	}
+	var have []Detector
+	for _, d := range Default(Runner(runner)) {
+		switch d.Name() {
+		case CapUplinkNetworkManager, CapUplinkSystemdNetworkd, CapUplinkDhcpcd:
+			have = append(have, d)
+		}
+	}
+	if len(have) != 3 {
+		t.Fatalf("expected a detector per manager, found %d", len(have))
+	}
+	for _, d := range have {
+		v := d.Detect(context.Background())
+		want := d.Name() == CapUplinkNetworkManager
+		if v.Present != want {
+			t.Errorf("%s: present=%v, want %v (%s)", d.Name(), v.Present, want, v.Detail)
+		}
+	}
+}