Fix Bluetooth bonding and record verified headphone relay fix

One-shot bluetoothctl pairing exited before SSP finished, leaving the
headphone paired but not bonded, so it was lost on reboot. Pair inside a
single bluetoothctl session with a persistent agent, and clear temporary
pairings first. Document that SBC medium + 500 ms buffer removed the
iPhone -> Radxa -> headphone dropouts, verified by listening and logs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/radxa-audio.py

@@ -269,12 +269,13 @@ def pair(addr, output=False, bond=False):
         raise ValueError('장비 주소 형식이 잘못됐습니다.')
     info = run('bluetoothctl', 'info', addr, check=False, capture=True).stdout
     if 'Paired: yes' not in info or (bond and 'Bonded: yes' not in info):
-        # Outgoing pairing agent lives only for this operation.
         controller = run('bluetoothctl', 'show', capture=True).stdout
         was_pairable = 'Pairable: yes' in controller
-        run('bluetoothctl', 'pairable', 'on')
+        if 'Paired: yes' in info:
+            # A temporary (unbonded) pairing blocks a new link key; start clean.
+            run('bluetoothctl', 'remove', addr, check=False, capture=True)
         try:
-            run('bluetoothctl', '--agent', 'NoInputNoOutput', '--timeout', '25', 'pair', addr, check=False)
+            agent_pair(addr)
         finally:
             if not was_pairable:
                 run('bluetoothctl', 'pairable', 'off', check=False)
@@ -294,6 +295,29 @@ def pair(addr, output=False, bond=False):
     print('페어링/신뢰 등록 완료:', addr)
 
 
+def agent_pair(addr, scan_seconds=12, pair_seconds=20):
+    """Pair inside one bluetoothctl session so the agent stays registered.
+
+    A one-shot `bluetoothctl --agent ... pair` can exit before Secure Simple
+    Pairing finishes, which leaves the device paired but not bonded.
+    """
+    import time
+    proc = subprocess.Popen(['bluetoothctl'], stdin=subprocess.PIPE, text=True)
+    steps = [('agent NoInputNoOutput', 1), ('default-agent', 1), ('pairable on', 1),
+             ('scan on', scan_seconds), ('scan off', 1), ('pair ' + addr, pair_seconds)]
+    try:
+        for command, wait in steps:
+            proc.stdin.write(command + '\n')
+            proc.stdin.flush()
+            time.sleep(wait)
+        proc.stdin.write('quit\n')
+        proc.stdin.flush()
+        proc.wait(timeout=10)
+    except (OSError, subprocess.TimeoutExpired):
+        proc.kill()
+        proc.wait()
+
+
 def main():
     p = argparse.ArgumentParser(description='Radxa AirPlay + Bluetooth 믹서 관리')
     sub = p.add_subparsers(dest='cmd', required=True)