fix: scanner catalog empty + left column blank

Scanner: new instance with existing sf_scan_state.json
did not populate in-memory _catalog. Now re-inspects
unchanged files to fill catalog on first scan.
Frontend: left column reads instrumentSelectorData.
soundfonts instead of sfPresets (null when no presets).
Click SF in left column triggers on-demand fetch.

app/core/soundfont_scanner.py

@@ -50,6 +50,22 @@ class SoundFontAutoScanner:
                 out.append((fname, os.path.join(directory, fname)))
         return out
 
+    def _inspect_single(self, fname: str, full: str, inspector) -> dict:
+        if fname.lower().endswith(".sf2"):
+            sf_info = inspector.inspect_sf2_file(full) or {}
+        else:
+            sf_info = {}
+        if not sf_info.get("soundfont_id"):
+            sf_id = os.path.splitext(fname)[0].lower()
+            sf_info = {
+                "soundfont_id": sf_id,
+                "filename": fname,
+                "total_instruments": 0,
+                "instruments": [],
+                "_sf3": True
+            }
+        return sf_info
+
     def scan_once(self) -> bool:
         from app.core.soundfont_inspector import SoundFontInspector
         inspector = SoundFontInspector(self.system_sf_dir, self.upload_sf_dir)
@@ -64,23 +80,19 @@ class SoundFontAutoScanner:
                 key = f"{source}:{sf_id}"
                 sig = _file_sig(full)
                 prev = self._state.get(key)
-                if prev and prev["size"] == sig[0] and prev["mtime"] == sig[1]:
+                unchanged = prev and prev["size"] == sig[0] and prev["mtime"] == sig[1]
+                if unchanged and sf_id in self._catalog:
+                    continue
+                if unchanged:
+                    with self._lock:
                         if sf_id in self._catalog:
                             continue
+                        sf_info = self._inspect_single(fname, full, inspector)
+                        self._catalog[sf_id] = sf_info
+                    continue
                 found_new = True
                 logger.info("New/changed SF detected: %s", fname)
-                if fname.lower().endswith(".sf2"):
-                    sf_info = inspector.inspect_sf2_file(full) or {}
-                else:
-                    sf_info = {}
-                if not sf_info.get("soundfont_id"):
-                    sf_info = {
-                        "soundfont_id": sf_id,
-                        "filename": fname,
-                        "total_instruments": 0,
-                        "instruments": [],
-                        "_sf3": True
-                    }
+                sf_info = self._inspect_single(fname, full, inspector)
                 with self._lock:
                     self._catalog[sf_id] = sf_info
                     self._state[key] = {"size": sig[0], "mtime": sig[1], "file": fname}

app/static/js/app.jsx

@@ -17704,15 +17704,29 @@ const App = () => {
           onClick: () => { setSelectedSoundFontId(null); setSynthCategory(null); },
           className: "w-full text-left px-3 py-2 text-sm rounded " + (!selectedSoundFontId ? "bg-amber-700 text-white" : "bg-zinc-800 hover:bg-zinc-700 text-zinc-300")
         }, "All Instruments"),
-        sfPresets === null ? (
-          /*#__PURE__*/React.createElement("p", { className: "text-sm text-zinc-500 py-2" }, "Loading...")
-        ) : (
-          [...new Map(sfPresets.map(p => [p._sfId, p])).values()].map(sf => /*#__PURE__*/React.createElement("button", {
-            key: sf._sfId,
-            onClick: () => setSelectedSoundFontId(sf._sfId),
-            className: "w-full text-left px-3 py-2 text-sm rounded " + (selectedSoundFontId === sf._sfId ? "bg-amber-700 text-white" : "bg-zinc-800 hover:bg-zinc-700 text-zinc-300")
-          }, sf._sfName))
-        )
+        (instrumentSelectorData?.soundfonts || []).map(sf => {
+          const sfId = sf.id.startsWith('sf_') ? sf.id : 'sf_' + sf.id;
+          const sfName = sf.display || sf.name || sf.id;
+          return /*#__PURE__*/React.createElement("button", {
+            key: sfId,
+            onClick: () => {
+              setSelectedSoundFontId(sfId);
+              // Fetch instruments on demand if not yet loaded
+              if (!sf.presets && window.SonicAPI) {
+                const baseId = sfId.replace('sf_', '');
+                window.SonicAPI.listSoundfontInstruments(baseId).then(data => {
+                  if (data && data.presets) {
+                    const mapping = data.presets.map(p => ({ ...p, _sfId: sfId, _sfName: sfName, _sfDisplay: sfName.substring(0, 30) }));
+                    setSfPresets(prev => prev ? [...prev, ...mapping] : mapping);
+                    // Also update instrumentSelectorData cache
+                    setInstrumentSelectorData(prev => prev ? { ...prev, soundfonts: (prev.soundfonts || []).map(s => s.id === sf.id ? { ...s, presets: data.presets } : s) } : prev);
+                  }
+                }).catch(() => {});
+              }
+            },
+            className: "w-full text-left px-3 py-2 text-sm rounded " + (selectedSoundFontId === sfId ? "bg-amber-700 text-white" : "bg-zinc-800 hover:bg-zinc-700 text-zinc-300")
+          }, sfName);
+        })
       ),
       /*#__PURE__*/React.createElement("div", { className: "flex-1 overflow-y-auto space-y-0.5" },
         /*#__PURE__*/React.createElement("button", {