The node-engine reports reads-wants; a failed apply is said; the have's fingerprint and digest follow its health (R6-A A6)

internal/agent/agent.go

@@ -491,6 +491,7 @@ func (a *Agent) apply(ctx context.Context, module string, w wantNow, comp compNo
 	if res.Failed {
 		a.attempt[module] = attempt{FP: fp, Composed: dig, WantRev: w.Rev, CompRev: comp.Rev}
 		a.mu.Unlock()
+		a.env.Say(fmt.Sprintf("applying %s at %s failed: %s", module, fp, res.Detail))
 		a.env.Haves.Write(ctx, Have{Module: module, FP: fp, Composed: dig, Phase: string(delivery.PhaseFailed), Detail: res.Detail})
 		return
 	}

internal/link/have_test.go

@@ -461,3 +461,40 @@ func TestTheFirstHaveWrittenIsToldToTheProof(t *testing.T) {
 		t.Fatal("a have already saying the same was not told")
 	}
 }
+
+// R6-A AC6: an applied module's have names its fingerprint and the digest of the composition applied; a health check that
+// fails after the module's start window gives health failed, and the have keeps both.
+func TestAnAppliedModulesHaveNamesTheFingerprintAndTheDigestAndFollowsItsHealth(t *testing.T) {
+	l := newHaveLink()
+	q, _ := aHaveQueue(l)
+	fp := "src2:" + strings.Repeat("a", 64)
+	dig := "sha256:" + strings.Repeat("b", 64)
+	q.NoteModule(context.Background(), ModuleFact{Module: "web", FP: fp, Composed: dig})
+	h := l.have(t, "n1.web")
+	if h.FP != fp || h.Composed != dig || h.Phase != delivery.PhaseRunning || h.Health != delivery.HealthUnknown {
+		t.Fatalf("the have after the apply: %+v", h)
+	}
+	// Starting: it waits. Past its start window the check fails: failed.
+	q.SayHealth(context.Background(), *healthOf(map[string]string{"web": StateStarting}))
+	if got := l.have(t, "n1.web"); got.Health != delivery.HealthWaits || got.FP != fp || got.Composed != dig {
+		t.Fatalf("while it starts: %+v", got)
+	}
+	q.SayHealth(context.Background(), *healthOf(map[string]string{"web": StateUnhealthy}))
+	if got := l.have(t, "n1.web"); got.Health != delivery.HealthFailed || got.FP != fp || got.Composed != dig {
+		t.Fatalf("a failing check after the start window: %+v", got)
+	}
+
+	// A module held for a failed backup says so and what it keeps running; removed is written once, over its key.
+	q.NoteModule(context.Background(), ModuleFact{Module: "web", FP: fp, Composed: dig, Phase: string(delivery.PhaseHeld), Detail: "the repository is locked"})
+	if got := l.have(t, "n1.web"); got.Phase != delivery.PhaseHeld || got.Detail == "" {
+		t.Fatalf("held: %+v", got)
+	}
+	q.NoteRemoved(context.Background(), "web", "")
+	if got := l.have(t, "n1.web"); got.Phase != delivery.PhaseRemoved {
+		t.Fatalf("removed: %+v", got)
+	}
+	q.NoteNode(context.Background(), dig)
+	if n, err := delivery.DecodeHaveNode(l.kv["n1.node"].value); err != nil || n.Composed != dig {
+		t.Fatalf("the node key: %+v %v", n, err)
+	}
+}

internal/profile/detectors.go

@@ -40,6 +40,11 @@ const (
 	// controller sends the field only to a node that reports it, since an older node-engine refuses the key.
 	CapContainerGroups = "container-groups"
 
+	// CapReadsWants says this node-engine follows its wants (novox/hq ADR 0539 §9): it watches `want.<node>.>` and its
+	// compositions and applies one module at a time, and hears no declaration. A fact about the program: the controller
+	// stops sending a node declarations only once it reports it.
+	CapReadsWants = "reads-wants"
+
 	// 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
@@ -190,6 +195,20 @@ func (containerGroups) Detect(context.Context) Verdict {
 	}
 }
 
+// readsWants reports that this node-engine follows its wants. True of the program that is running, so it is always
+// present: its absence on a node is what tells the controller the node-engine still waits for declarations.
+type readsWants struct{}
+
+func (readsWants) Name() string { return CapReadsWants }
+
+func (readsWants) Detect(context.Context) Verdict {
+	return Verdict{
+		Name: CapReadsWants, Present: true,
+		Detail: "follows its wants and applies one module's composition at a time; hears no declaration",
+		How:    "a fact about this program, not probed: the node-engine that answers follows its wants",
+	}
+}
+
 // graphicalSession reports whether anything could display a window here.
 //
 // Environment rather than a probe, because a display server is reachable through a socket a
@@ -230,6 +249,7 @@ func Default(runner Runner) []Detector {
 		privileged{},
 		fileReferences{},
 		containerGroups{},
+		readsWants{},
 		graphicalSession{},
 		seat{},
 		battery{},

internal/profile/reads_wants_test.go

@@ -0,0 +1,22 @@
+package profile
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+// R6-A: the node's profile carries the capability that says the node-engine follows its wants, which the controller
+// checks before it stops sending the node declarations (novox/hq ADR 0539 §9).
+func TestTheProfileSaysTheNodeEngineReadsItsWants(t *testing.T) {
+	got := Detect(context.Background(), Default(func(context.Context, string, ...string) (string, error) {
+		return "", nil
+	}), time.Second)
+	v := verdictOf(t, got, CapReadsWants)
+	if !v.Present || v.Detail == "" || v.How == "" {
+		t.Errorf("reads-wants = %+v, want present with a detail and a method", v)
+	}
+	if CapReadsWants != "reads-wants" {
+		t.Errorf("the capability is named %q", CapReadsWants)
+	}
+}