feat(streams): run live streams under the xc_fanout monitor, copy-only ones on its native remuxer

With fanout_supervise on, StreamProcess::startMonitor() no longer spawns a
PHP watchdog. It builds the stream's commands and hands them to the
daemon's supervisor (PUT /monitor/<id>), which starts, watches and
restarts them: failover, priority backup, forced source, stalled output,
audio loss, frame-rate drop and scheduled restart. PHP still builds every
command and makes every database write.

A copy-only live stream's command is the daemon's native remuxer,
`xc_fanout remux`, composed by the new buildNativeLive() exactly as
buildLive() composes an ffmpeg line. It reads the source natively and
writes the same on-disk HLS and daemon feed as the ffmpeg -f tee output,
with no ffmpeg process. fanout_source_backend decides: auto = remuxer with
the ffmpeg command as fallback_cmd (taken when the remuxer exits 3,
"cannot serve this source": fMP4 or encrypted HLS, rtmp, no keyframes),
native = remuxer only, ffmpeg = ffmpeg only. Eligibility is explicit
(isNativeEligible / isNativeSource): no transcode, custom ffmpeg, custom
map, RTMP output, external push, timestamp repair, read-native or forced
input codec; http(s)/udp/rtp sources only.

The rest of the panel learns who owns the producer:

- superviseStream() asks the daemon first and touches nothing unless it
  is accepting; without a restart it adopts a running encoder, so
  cron:streams moves PHP-monitored streams over with no blip. A producer
  the daemon cannot adopt (PHP LLOD, PHP loopback) is replaced, never left
  beside the new one. The row is marked watched before the hand-over, so
  the reconcile cannot release a stream mid-start.
- reconcileSupervised() copies the daemon's state (status, pid, source,
  codecs, resolution, measured bitrate) into streams_servers: every
  cron:streams pass and every 5 s from the signals daemon. Supervised
  streams whose row is gone or stopped are released.
- stopStream() and the on-demand reaper release before killing anything;
  killing the producer first is what the supervisor restarts.
- isWatched() replaces bare isMonitorAlive() checks in live.php,
  admin/live.php, rtmp.php and cron:streams: a supervised stream's
  monitor_pid is the daemon's. MonitorCommand stands down for supervised
  streams; startMonitor() releases one before falling back to PHP, so
  turning supervision off does bring streams back on their next restart.
- force_stream goes through the daemon for a supervised stream (the .force
  file is only read by the PHP monitor).
- ProcessManager::isStreamRunning() recognises the remuxer, so the
  archive, thumbnail and delay workers follow it like ffmpeg.
- A supervised loopback child tees into the daemon (the supervisor judges
  a stream by the bytes it receives); legacy loopback is unchanged.

Delay streams, created channels and yt-dlp platform sources stay on the
PHP monitor. A daemon without /monitors/state (older than this) is never
handed a stream, so the panel is safe against an un-upgraded node.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012QL93N6dzGkmKoQgA4oh16

tests/Unit/StreamProcessBuildLiveTest.php

@@ -120,6 +120,30 @@ final class StreamProcessBuildLiveTest extends TestCase {
 		$this->assertStringContainsString('echo $! > ' . STREAMS_PATH . '42_.pid', $out);
 	}
 
+	// ── supervised (launched by the fanout daemon) ─────────────
+
+	/** The daemon is the parent: the shell's redirect/background/pid tail must go. */
+	public function testSupervisedOmitsTheLaunchTail(): void {
+		$out = $this->build(['supervised' => true]);
+		$this->assertStringNotContainsString('>/dev/null', $out);
+		$this->assertStringNotContainsString('echo $!', $out);
+		$this->assertStringNotContainsString(' & ', $out);
+		$this->assertStringContainsString(STREAMS_PATH . '42_.m3u8', $out, 'still names its playlist (adopt_match)');
+	}
+
+	/** A supervised loopback feeds the daemon, which confirms and judges it by those bytes. */
+	public function testSupervisedLoopbackTeesIntoTheDaemon(): void {
+		$out = $this->build(['loopback' => true, 'ingestSock' => '/run/ingest/42.sock', 'supervised' => true]);
+		$this->assertStringContainsString('-f tee', $out);
+		$this->assertStringContainsString('unix:/run/ingest/42.sock', $out);
+		$this->assertStringContainsString('-map 0 -copy_unknown', $out);
+	}
+
+	/** The legacy path registers no ingest for loopback and must stay on-disk only. */
+	public function testLegacyLoopbackStaysOnDiskOnly(): void {
+		$this->assertStringNotContainsString('-f tee', $this->build(['loopback' => true]));
+	}
+
 	// ── custom_ffmpeg branch ───────────────────────────────────
 
 	public function testCustomFfmpegBypassesTemplate(): void {