feat(atlas): hybrid substrate — live specs for cluster nodes, authored rest

MergeSubstrate overlays live node specs onto the authored machine list by name:
cluster nodes (koala) get fresh live specs, non-cluster machines (iguana/flamingo/
piguard) stay authored, new live nodes are appended. Test-first. Restores the full
homelab machine list while keeping cluster nodes truthful.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/atlas/cluster.go

@@ -52,6 +52,33 @@ func HostsFromNodes(nodesJSON []byte) ([]Host, error) {
 	return hosts, nil
 }
 
+// MergeSubstrate overlays live node specs onto the authored substrate: an
+// authored host is replaced by the live node of the same name (fresh specs),
+// authored-only machines (non-cluster: iguana/flamingo/piguard) are kept, and
+// live-only nodes (new to the cluster) are appended.
+func MergeSubstrate(authored, live []Host) []Host {
+	liveByName := make(map[string]Host, len(live))
+	for _, h := range live {
+		liveByName[h.Name] = h
+	}
+	seen := make(map[string]bool, len(authored))
+	out := make([]Host, 0, len(authored)+len(live))
+	for _, a := range authored {
+		if l, ok := liveByName[a.Name]; ok {
+			out = append(out, l)
+		} else {
+			out = append(out, a)
+		}
+		seen[a.Name] = true
+	}
+	for _, l := range live {
+		if !seen[l.Name] {
+			out = append(out, l)
+		}
+	}
+	return out
+}
+
 // memGi converts a Kubernetes memory quantity in Ki (e.g. "67108864Ki") to a
 // rounded Gi string. Returns "" if unparseable.
 func memGi(ki string) string {

internal/atlas/cluster_test.go

@@ -31,6 +31,37 @@ func TestHostsFromNodes_DerivesSpecFromNodeStatus(t *testing.T) {
 	}
 }
 
+func TestMergeSubstrate_LiveOverridesAuthoredKeepsRestAppendsNew(t *testing.T) {
+	authored := []atlas.Host{
+		{Name: "koala", Spec: "RTX 5070 · authored"},
+		{Name: "iguana", Spec: "M2 Ultra · Ollama / mlx"},
+		{Name: "piguard", Spec: "NGINX reverse-proxy · ntfy"},
+	}
+	live := []atlas.Host{
+		{Name: "koala", Spec: "amd64 · 16 cpu · 60Gi · 1× GPU · k3s v1.34.5"},
+		{Name: "worker9", Spec: "arm64 · 4 cpu"},
+	}
+
+	got := atlas.MergeSubstrate(authored, live)
+	want := []atlas.Host{
+		{Name: "koala", Spec: "amd64 · 16 cpu · 60Gi · 1× GPU · k3s v1.34.5"}, // live wins
+		{Name: "iguana", Spec: "M2 Ultra · Ollama / mlx"},                     // authored kept
+		{Name: "piguard", Spec: "NGINX reverse-proxy · ntfy"},                 // authored kept
+		{Name: "worker9", Spec: "arm64 · 4 cpu"},                              // live-only appended
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("merge = %+v\nwant   %+v", got, want)
+	}
+}
+
+func TestMergeSubstrate_NoLiveReturnsAuthored(t *testing.T) {
+	authored := []atlas.Host{{Name: "koala", Spec: "authored"}}
+	got := atlas.MergeSubstrate(authored, nil)
+	if !reflect.DeepEqual(got, authored) {
+		t.Fatalf("merge with no live = %+v, want %+v", got, authored)
+	}
+}
+
 func TestHostsFromNodes_ErrorsOnBadJSON(t *testing.T) {
 	if _, err := atlas.HostsFromNodes([]byte("{not json")); err == nil {
 		t.Fatal("expected error on bad JSON, got nil")

internal/web/handler.go

@@ -38,7 +38,7 @@ func NewHandler() http.Handler {
 			return
 		}
 		if live := liveSubstrate(); len(live) > 0 {
-			a.Substrate = live
+			a.Substrate = atlas.MergeSubstrate(a.Substrate, live)
 		}
 		w.Header().Set("Content-Type", "application/json; charset=utf-8")
 		_ = json.NewEncoder(w).Encode(a)