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.

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)
+		}
+	}
+}