fix: narrow SHM cleanup in profile handler to client semaphore only; add DC-blocking HPF to pipeline input (60Hz hum fix)

src/web/server.py

@@ -1768,14 +1768,15 @@ class WebServer:
             # Clean stale client SHM before creating new JACK client.
             # The old process's jack.Client __del__ can recreate the
             # pi-multifx semaphore after stop_jack() cleaned it.
+            # IMPORTANT: Only target our client's semaphore, NOT the
+            # running JACK server's files (jack_sem.*_system, jack-shm-registry,
+            # jack_db-0/) — deleting those between start_jack() and
+            # jack_client.start() kills the JACK server socket and makes
+            # the client connection fail silently.
             try:
                 from pathlib import Path
-                import shutil
-                for p in Path("/dev/shm").glob("jack*"):
-                    if p.is_dir():
-                        shutil.rmtree(p, ignore_errors=True)
-                    else:
-                        p.unlink(missing_ok=True)
+                for p in Path("/dev/shm").glob("jack_sem.*.default_pi-multifx*"):
+                    p.unlink(missing_ok=True)
             except Exception:
                 pass