feat(k8s): Longhorn Platform component (F1) (#147)

Add `longhorn` to the opt-in Platform component set (chart `longhorn`
from charts.longhorn.io, namespace longhorn-system): replicated block
storage — RWO volumes with node-to-node replication + snapshots, the
tier NFS/local-path don't cover.

#Platform.longhorn? schema entry + unit test (chart/ns defaults, values
thread-through). Every node needs open-iscsi, installable via a k3s
worker pool's nodePrep.packages (E2) — documented in the component
comment and schema — or Longhorn's iscsi-installer DaemonSet as a
fallback. Opt-in like every component: platform.longhorn.enabled: true.

Author: astrojerms

ROADMAP.md

@@ -184,10 +184,16 @@ prerequisite (Longhorn); the rest are convenience + robustness.
       the prereqs. **Makes F1 (Longhorn) usable.**
 
 ### F. Storage
-- [ ] **F1 — Longhorn Platform component.** Add `longhorn` to the opt-in
-      Platform set (replicated block storage, the tier NFS/local-path don't
-      cover). Depends on E1 (open-iscsi on nodes); document the
-      iscsi-installer DaemonSet as the interim fallback.
+- [x] **F1 — Longhorn Platform component.** `longhorn` added to the opt-in
+      Platform set (chart `longhorn` from `charts.longhorn.io`, ns
+      `longhorn-system`) — replicated block storage (RWO volumes with
+      node-to-node replication + snapshots), the tier NFS/local-path don't
+      cover. `#Platform.longhorn?` schema entry + unit test (chart/ns defaults,
+      values thread-through). Every node needs `open-iscsi`: install it via a
+      k3s worker pool's `nodePrep.packages` (**E2**, now shipped) — documented in
+      both the component comment and schema — or Longhorn's own iscsi-installer
+      DaemonSet as the interim fallback. Enabling is `platform.longhorn.enabled:
+      true`.
 
 ### G. Public exposure
 - [ ] **G1 — expose-app convenience.** A composite (or documented pattern)

plugins/k8s/internal/provider/platform.go

@@ -52,6 +52,12 @@ var platformComponents = []component{
 	// persistent volumes on request. Set nfsProvisioner.values.nfs.{server,path}
 	// to the NAS export.
 	{"nfsProvisioner", "https://kubernetes-sigs.github.io/nfs-subdir-external-provisioner", "nfs-subdir-external-provisioner", "nfs-provisioner"},
+	// longhorn is replicated block storage — the tier NFS/local-path don't
+	// cover (RWO volumes with node-to-node replication + snapshots). Every node
+	// needs `open-iscsi` installed; provision it via a k3s worker pool's
+	// nodePrep (E2) — e.g. nodePrep.packages: ["open-iscsi"] — or Longhorn's
+	// own iscsi-installer DaemonSet as an interim fallback.
+	{"longhorn", "https://charts.longhorn.io", "longhorn", "longhorn-system"},
 }
 
 // releaseCoord locates an installed component release for Get/Delete/prune.

plugins/k8s/internal/provider/platform_test.go

@@ -71,6 +71,33 @@ func TestEnabledComponents_NfsProvisioner(t *testing.T) {
 	}
 }
 
+func TestEnabledComponents_Longhorn(t *testing.T) {
+	comps := enabledComponents(map[string]any{
+		"longhorn": map[string]any{
+			"enabled": true,
+			"values":  map[string]any{"defaultSettings": map[string]any{"defaultReplicaCount": 2}},
+		},
+	})
+	if len(comps) != 1 {
+		t.Fatalf("enabled = %d, want 1 (longhorn)", len(comps))
+	}
+	c := comps[0]
+	if c.comp.name != "longhorn" {
+		t.Errorf("component = %q", c.comp.name)
+	}
+	if c.chart.Repo != "https://charts.longhorn.io" || c.chart.Name != "longhorn" {
+		t.Errorf("chart defaults wrong: %+v", c.chart)
+	}
+	if c.opts.namespace != "longhorn-system" {
+		t.Errorf("default namespace = %q, want longhorn-system", c.opts.namespace)
+	}
+	// User values (e.g. replica count) thread through to the chart.
+	ds, _ := c.values["defaultSettings"].(map[string]any)
+	if ds["defaultReplicaCount"] != 2 {
+		t.Errorf("longhorn values not threaded: %+v", c.values)
+	}
+}
+
 func TestEnabledComponents_NvidiaDevicePlugin(t *testing.T) {
 	comps := enabledComponents(map[string]any{
 		"nvidiaDevicePlugin": map[string]any{"enabled": true},

plugins/k8s/internal/provider/schema.go

@@ -112,6 +112,11 @@ const platformSchema = `
 		// nfsProvisioner gives a dynamic NFS-backed StorageClass for persistent
 		// volumes (e.g. a Synology share). Set values.nfs.server + values.nfs.path.
 		nfsProvisioner?: {...}
+		// longhorn is replicated block storage (RWO volumes with node-to-node
+		// replication + snapshots). Every node needs open-iscsi — install it via
+		// a k3s worker pool's nodePrep.packages, or Longhorn's iscsi-installer
+		// DaemonSet as a fallback.
+		longhorn?: {...}
 	}
 	...
 }