feat: built-in volume management

- Volume slider on every node (green bar, draggable)
- Mute toggle button (M/m) on every node
- Backend: read volume/mute from PipeWire node props
- Backend: POST /api/volume {node_id, volume} to set volume
- Backend: POST /api/mute {node_id, mute} to toggle mute
- Graph JSON includes volume and mute fields per node
- Slider supports drag-to-adjust with mouse

frontend/src/components/GraphCanvas.svelte

@@ -11,6 +11,7 @@
     setActivated, setExclusive,
     setAutoPin, setAutoDisconnect,
     saveProfile, loadProfile, deleteProfile,
+    setNodeVolume, setNodeMute,
   } from '../lib/stores';
   import type { Node, Port, Link } from '../lib/types';
 
@@ -166,7 +167,7 @@
       const headerH = 22;
       const portH = 16;
       const maxPorts = Math.max(allInPorts.length, allOutPorts.length, 1);
-      const height = headerH + maxPorts * portH + 4;
+      const height = headerH + maxPorts * portH + 20; // extra 20 for volume slider
       const width = 220;
 
       const portPositions = new Map<number, { x: number; y: number }>();
@@ -476,6 +477,48 @@
             <circle cx={nd.x + nd.width} cy={py} r="3" fill="#333" />
           {/if}
         {/each}
+
+        <!-- Volume slider + mute button at bottom of node -->
+        <!-- Mute button -->
+        <rect
+          x={nd.x + nd.width - 24} y={nd.y + nd.height - 17} width="16" height="12" rx="2"
+          fill={nd.mute ? '#a44' : '#2a2a3e'} stroke="#555" stroke-width="0.5"
+          style="cursor:pointer"
+          onclick={() => setNodeMute(nd.id, !nd.mute)}
+        />
+        <text
+          x={nd.x + nd.width - 16} y={nd.y + nd.height - 8}
+          font-size="8" font-family="monospace" fill={nd.mute ? '#fff' : '#888'}
+          text-anchor="middle" style="pointer-events:none"
+        >{nd.mute ? 'M' : 'm'}</text>
+        <!-- Volume bar background -->
+        <rect x={nd.x + 8} y={nd.y + nd.height - 12} width={nd.width - 36} height="3" rx="1.5" fill="#333" />
+        <!-- Volume bar fill -->
+        <rect x={nd.x + 8} y={nd.y + nd.height - 12} width={(nd.width - 36) * Math.min(nd.volume, 1)} height="3" rx="1.5" fill={nd.mute ? '#666' : '#4a9'} />
+        <!-- Volume slider hit area -->
+        <rect
+          x={nd.x + 8} y={nd.y + nd.height - 16} width={nd.width - 36} height="11"
+          fill="transparent" style="cursor:pointer"
+          onmousedown={(e) => {
+            e.stopPropagation();
+            const svgRect = svgEl?.getBoundingClientRect();
+            if (!svgRect) return;
+            const vbx = nd.x + 8;
+            const vbw = nd.width - 36;
+            const onMove = (ev: MouseEvent) => {
+              const ratio = (ev.clientX - svgRect.left - (vbx - viewBox.x) * svgRect.width / viewBox.w) / (vbw * svgRect.width / viewBox.w);
+              setNodeVolume(nd.id, Math.max(0, Math.min(1.5, ratio)));
+            };
+            const onUp = () => { window.removeEventListener('mousemove', onMove); window.removeEventListener('mouseup', onUp); };
+            window.addEventListener('mousemove', onMove);
+            window.addEventListener('mouseup', onUp);
+          }}
+        />
+        <!-- Volume % label -->
+        <text x={nd.x + 8} y={nd.y + nd.height - 14} font-size="7" font-family="monospace" fill="#666">
+          {Math.round(nd.volume * 100)}%
+        </text>
+
       </g>
     {/each}
   </svg>

frontend/src/lib/stores.ts

@@ -358,4 +358,29 @@ export function deleteProfile(name: string) {
   savePatchbayState();
 }
 
+// Volume control
+export async function setNodeVolume(nodeId: number, volume: number) {
+  try {
+    await fetch('/api/volume', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ node_id: nodeId, volume }),
+    });
+  } catch (e) {
+    console.error('[api] volume failed:', e);
+  }
+}
+
+export async function setNodeMute(nodeId: number, mute: boolean) {
+  try {
+    await fetch('/api/mute', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ node_id: nodeId, mute }),
+    });
+  } catch (e) {
+    console.error('[api] mute failed:', e);
+  }
+}
+
 export { connectPorts, disconnectPorts };

frontend/src/lib/types.ts

@@ -16,6 +16,8 @@ export interface Node {
   media_name: string;
   mode: 'input' | 'output' | 'duplex' | 'none';
   node_type: string;
+  volume: number;
+  mute: boolean;
   port_ids: number[];
 }
 

src/graph_engine.cpp

@@ -3,6 +3,10 @@
 #include <pipewire/pipewire.h>
 #include <spa/utils/result.h>
 #include <spa/utils/list.h>
+#include <spa/param/props.h>
+#include <spa/pod/pod.h>
+#include <spa/pod/builder.h>
+#include <spa/pod/iter.h>
 
 #include <cstring>
 #include <algorithm>
@@ -65,16 +69,30 @@ static void on_node_info(void *data, const struct pw_node_info *info) {
     info = pw_node_info_update((struct pw_node_info*)obj->info, info);
     obj->info = (void*)info;
 
-    if (info && (info->change_mask & PW_NODE_CHANGE_MASK_PROPS)) {
     auto *nobj = static_cast<GraphEngine::NodeObj*>(obj);
+
+    if (info && (info->change_mask & PW_NODE_CHANGE_MASK_PROPS)) {
         if (info->props) {
             const char *media_name = spa_dict_lookup(info->props, PW_KEY_MEDIA_NAME);
             if (media_name && strlen(media_name) > 0)
                 nobj->node.media_name = media_name;
+
+            // Read volume from props
+            const char *vol_str = spa_dict_lookup(info->props, "volume");
+            if (vol_str) {
+                nobj->node.volume = pw_properties_parse_float(vol_str);
             }
+
+            // Read mute from props
+            const char *mute_str = spa_dict_lookup(info->props, "mute");
+            if (mute_str) {
+                nobj->node.mute = pw_properties_parse_bool(mute_str);
+            }
+        }
+    }
+
     nobj->node.changed = true;
     nobj->node.ready = true;
-    }
 }
 
 static const struct pw_node_events node_events = {
@@ -770,4 +788,65 @@ bool GraphEngine::disconnectPorts(uint32_t output_port_id, uint32_t input_port_i
     return found;
 }
 
+// ============================================================================
+// Volume control
+// ============================================================================
+
+bool GraphEngine::setNodeVolume(uint32_t node_id, float volume) {
+    if (!m_pw.loop) return false;
+
+    pw_thread_loop_lock(m_pw.loop);
+
+    NodeObj *nobj = findNode(node_id);
+    if (!nobj || !nobj->proxy) {
+        pw_thread_loop_unlock(m_pw.loop);
+        return false;
+    }
+
+    // Build Props param with volume
+    uint8_t buf[1024];
+    struct spa_pod_builder b = SPA_POD_BUILDER_INIT(buf, sizeof(buf));
+
+    struct spa_pod *param = (struct spa_pod*)spa_pod_builder_add_object(&b,
+        SPA_TYPE_OBJECT_Props, SPA_PARAM_Props,
+        SPA_PROP_volume, SPA_POD_Float(volume));
+
+    pw_node_set_param((pw_node*)nobj->proxy,
+        SPA_PARAM_Props, 0, param);
+
+    nobj->node.volume = volume;
+    nobj->node.changed = true;
+
+    pw_thread_loop_unlock(m_pw.loop);
+    return true;
+}
+
+bool GraphEngine::setNodeMute(uint32_t node_id, bool mute) {
+    if (!m_pw.loop) return false;
+
+    pw_thread_loop_lock(m_pw.loop);
+
+    NodeObj *nobj = findNode(node_id);
+    if (!nobj || !nobj->proxy) {
+        pw_thread_loop_unlock(m_pw.loop);
+        return false;
+    }
+
+    uint8_t buf[1024];
+    struct spa_pod_builder b = SPA_POD_BUILDER_INIT(buf, sizeof(buf));
+
+    struct spa_pod *param = (struct spa_pod*)spa_pod_builder_add_object(&b,
+        SPA_TYPE_OBJECT_Props, SPA_PARAM_Props,
+        SPA_PROP_mute, SPA_POD_Bool(mute));
+
+    pw_node_set_param((pw_node*)nobj->proxy,
+        SPA_PARAM_Props, 0, param);
+
+    nobj->node.mute = mute;
+    nobj->node.changed = true;
+
+    pw_thread_loop_unlock(m_pw.loop);
+    return true;
+}
+
 // end of graph_engine.cpp

src/graph_engine.h

@@ -44,6 +44,10 @@ public:
     bool connectPorts(uint32_t output_port_id, uint32_t input_port_id);
     bool disconnectPorts(uint32_t output_port_id, uint32_t input_port_id);
 
+    // Volume control
+    bool setNodeVolume(uint32_t node_id, float volume);
+    bool setNodeMute(uint32_t node_id, bool mute);
+
     // PipeWire internal data (exposed for C callbacks)
     struct PwData {
         pw_thread_loop *loop;

src/graph_types.h

@@ -63,10 +63,15 @@ struct Node {
     bool        ready;
     bool        changed;
 
+    // Volume
+    float       volume;     // 0.0 - 1.0 (linear)
+    bool        mute;
+
     std::vector<uint32_t> port_ids;  // child port IDs
 
     Node() : id(0), mode(PortMode::None), node_type(NodeType::None),
-             mode2(PortMode::None), ready(false), changed(false) {}
+             mode2(PortMode::None), ready(false), changed(false),
+             volume(1.0f), mute(false) {}
 };
 
 struct Link;

src/web_server.cpp

@@ -109,6 +109,8 @@ std::string WebServer::buildGraphJson() const {
              << ",\"media_name\":\"" << escapeJson(n.media_name) << "\""
              << ",\"mode\":\"" << portModeStr(n.mode) << "\""
              << ",\"node_type\":\"" << nodeTypeStr(n.node_type) << "\""
+             << ",\"volume\":" << n.volume
+             << ",\"mute\":" << (n.mute ? "true" : "false")
              << ",\"port_ids\":[";
         bool first_p = true;
         for (uint32_t pid : n.port_ids) {
@@ -403,6 +405,47 @@ void WebServer::setupRoutes() {
         res.set_content(buf, "application/json");
         res.set_header("Access-Control-Allow-Origin", "*");
     });
+
+    // Volume: POST /api/volume {"node_id": N, "volume": 0.0-1.0}
+    m_http.Post("/api/volume", [this](const httplib::Request &req, httplib::Response &res) {
+        uint32_t node_id = 0;
+        float volume = 0;
+        if (sscanf(req.body.c_str(),
+                "{\"node_id\":%u,\"volume\":%f}", &node_id, &volume) == 2 ||
+            sscanf(req.body.c_str(),
+                "{\"node_id\":%u, \"volume\":%f}", &node_id, &volume) == 2)
+        {
+            if (volume < 0) volume = 0;
+            if (volume > 1.5) volume = 1.5;
+            bool ok = m_engine.setNodeVolume(node_id, volume);
+            if (ok) broadcastGraph();
+            res.set_content(ok ? "{\"ok\":true}" : "{\"ok\":false}", "application/json");
+        } else {
+            res.status = 400;
+            res.set_content("{\"error\":\"invalid json\"}", "application/json");
+        }
+        res.set_header("Access-Control-Allow-Origin", "*");
+    });
+
+    // Mute: POST /api/mute {"node_id": N, "mute": true/false}
+    m_http.Post("/api/mute", [this](const httplib::Request &req, httplib::Response &res) {
+        uint32_t node_id = 0;
+        if (sscanf(req.body.c_str(), "{\"node_id\":%u", &node_id) == 1 ||
+            sscanf(req.body.c_str(), "{\"node_id\": %u", &node_id) == 1)
+        {
+            bool mute = req.body.find("true") != std::string::npos;
+            bool ok = m_engine.setNodeMute(node_id, mute);
+            if (ok) broadcastGraph();
+            res.set_content(ok ? "{\"ok\":true}" : "{\"ok\":false}", "application/json");
+        } else {
+            res.status = 400;
+            res.set_content("{\"error\":\"invalid json\"}", "application/json");
+        }
+        res.set_header("Access-Control-Allow-Origin", "*");
+    });
+
+    m_http.Options("/api/volume", cors_handler);
+    m_http.Options("/api/mute", cors_handler);
 }
 
 // end of web_server.cpp