feat: save and restore virtual nodes (null-sinks, loopbacks) in profiles

- Add VirtualNodeDef type; track it in PatchbayState.virtual_nodes
- createNullSink/createLoopback now register the node in the global
  virtual_nodes registry on success
- Destroying a node via context menu removes it from the registry
- saveProfile snapshots virtual_nodes into the profile
- loadProfile recreates any missing virtual nodes before applying
  connections (waits 1.5s for graph to settle after creation)
- Backward compat: virtual_nodes defaults to [] for old save files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/GraphCanvas.svelte

@@ -12,7 +12,7 @@
     setAutoPin, setAutoDisconnect,
     saveProfile, loadProfile, deleteProfile,
     setNodeVolume, setNodeMute,
-    setAlias,
+    setAlias, removeVirtualNode,
     createNullSink, createLoopback, loadModule,
     getQuantum, setQuantum,
   } from '../lib/stores';
@@ -704,6 +704,7 @@
         nodeContextMenu = null;
       }}>Hide</button>
       <button onclick={() => {
+        removeVirtualNode(nodeContextMenu!.nodeName);
         fetch('/api/destroy-node', {
           method: 'POST',
           headers: { 'Content-Type': 'application/json' },

frontend/src/lib/stores.ts

@@ -1,5 +1,5 @@
 import { writable, derived } from 'svelte/store';
-import type { Node, Port, Link, GraphMessage, PatchbayState, PatchbayProfile, ConnectionRule } from './types';
+import type { Node, Port, Link, GraphMessage, PatchbayState, PatchbayProfile, ConnectionRule, VirtualNodeDef } from './types';
 import { subscribe, connectPorts, disconnectPorts } from './ws';
 
 // Raw graph stores
@@ -20,6 +20,7 @@ export const patchbay = writable<PatchbayState>({
   hide_rules: [],
   merge_rules: [],
   aliases: {},
+  virtual_nodes: [],
 });
 
 // Port/node lookups
@@ -83,7 +84,7 @@ export async function initGraph() {
     if (res.ok) {
       const data = await res.json();
       if (data && data.profiles) {
-        patchbay.set({ ...data, aliases: data.aliases ?? {} } as PatchbayState);
+        patchbay.set({ ...data, aliases: data.aliases ?? {}, virtual_nodes: data.virtual_nodes ?? [] } as PatchbayState);
       }
     }
   } catch {}
@@ -336,6 +337,7 @@ export async function saveProfile(name: string) {
     merge_rules: [...pb.merge_rules],
     volumes,
     mutes,
+    virtual_nodes: [...pb.virtual_nodes],
   };
 
   patchbay.update(pb => ({
@@ -346,6 +348,22 @@ export async function saveProfile(name: string) {
   savePatchbayState();
 }
 
+async function restoreVirtualNodes(defs: VirtualNodeDef[]) {
+  if (!defs.length) return;
+  const currentNodes = get_store_value(nodes);
+  const existingNames = new Set(currentNodes.map(n => n.name));
+  let created = false;
+  for (const vn of defs) {
+    if (!existingNames.has(vn.name)) {
+      if (vn.type === 'null-sink') await createNullSink(vn.name);
+      else if (vn.type === 'loopback') await createLoopback(vn.name);
+      created = true;
+    }
+  }
+  // Give the graph time to settle after creation before applying connections
+  if (created) await new Promise(r => setTimeout(r, 1500));
+}
+
 async function applyProfileVolumes(profile: PatchbayProfile) {
   if (!profile.volumes && !profile.mutes) return;
   const currentNodes = get_store_value(nodes);
@@ -370,13 +388,17 @@ async function applyProfileVolumes(profile: PatchbayProfile) {
   }
 }
 
-export function loadProfile(name: string) {
+export async function loadProfile(name: string) {
   patchbay.update(pb => ({ ...pb, active_profile: name }));
   const pb = get_store_value(patchbay);
-  // Always apply connections when explicitly loading a profile
-  applyPatchbay(pb);
   const profile = pb.profiles[name];
-  if (profile) applyProfileVolumes(profile);
+  if (!profile) { savePatchbayState(); return; }
+
+  // Recreate missing virtual nodes before restoring connections
+  await restoreVirtualNodes(profile.virtual_nodes ?? []);
+
+  applyPatchbay(pb);
+  applyProfileVolumes(profile);
   savePatchbayState();
 }
 
@@ -441,7 +463,15 @@ export async function createNullSink(name: string): Promise<number | null> {
       body: JSON.stringify({ name }),
     });
     const data = await res.json();
-    return data.module_id > 0 ? data.module_id : null;
+    const moduleId = data.module_id > 0 ? data.module_id : null;
+    if (moduleId) {
+      patchbay.update(pb => ({
+        ...pb,
+        virtual_nodes: [...pb.virtual_nodes.filter(v => v.name !== name), { type: 'null-sink', name }],
+      }));
+      savePatchbayState();
+    }
+    return moduleId;
   } catch (e) {
     console.error('[api] create-null-sink failed:', e);
     return null;
@@ -456,13 +486,29 @@ export async function createLoopback(name: string): Promise<number | null> {
       body: JSON.stringify({ name }),
     });
     const data = await res.json();
-    return data.module_id > 0 ? data.module_id : null;
+    const moduleId = data.module_id > 0 ? data.module_id : null;
+    if (moduleId) {
+      patchbay.update(pb => ({
+        ...pb,
+        virtual_nodes: [...pb.virtual_nodes.filter(v => v.name !== name), { type: 'loopback', name }],
+      }));
+      savePatchbayState();
+    }
+    return moduleId;
   } catch (e) {
     console.error('[api] create-loopback failed:', e);
     return null;
   }
 }
 
+export function removeVirtualNode(name: string) {
+  patchbay.update(pb => ({
+    ...pb,
+    virtual_nodes: pb.virtual_nodes.filter(v => v.name !== name),
+  }));
+  savePatchbayState();
+}
+
 export async function loadModule(module: string, args: string): Promise<number | null> {
   try {
     const res = await fetch('/api/load-module', {

frontend/src/lib/types.ts

@@ -57,6 +57,12 @@ export interface DisconnectMessage {
 
 export type WsMessage = ConnectMessage | DisconnectMessage;
 
+// Virtual device definition (user-created null-sinks, loopbacks, etc.)
+export interface VirtualNodeDef {
+  type: 'null-sink' | 'loopback';
+  name: string;
+}
+
 // Patchbay types
 export interface ConnectionRule {
   output_port_name: string;
@@ -75,6 +81,7 @@ export interface PatchbayProfile {
   merge_rules?: string[];
   volumes?: Record<string, number>;     // PW node name → volume (0..1)
   mutes?: Record<string, boolean>;      // PW node name → mute state
+  virtual_nodes?: VirtualNodeDef[];     // user-created virtual devices
 }
 
 export interface PatchbayState {
@@ -88,4 +95,5 @@ export interface PatchbayState {
   hide_rules: string[];
   merge_rules: string[];
   aliases: Record<string, string>;      // PW node name → custom display name
+  virtual_nodes: VirtualNodeDef[];      // user-created virtual devices (global registry)
 }