fix(quickemu): detect audio backends via sockets, not pidof

[flexiondotorg]

• Replace process checks (pidof pipewire / pidof pulseaudio) with socket existence checks to determine functional audio services.
• PipeWire detection checks $PIPEWIRE_REMOTE or $XDG_RUNTIME_DIR/pipewire-0.
• PulseAudio detection checks $PULSE_SERVER or $XDG_RUNTIME_DIR/pulse/native.
• Change default audio driver from pa to alsa as a safer fallback on headless hosts.
• Set detection priority: PipeWire (if QEMU >= 8.1) → PulseAudio → ALSA.
• Reason: a listening socket indicates a working service; pidof can be misleading on headless servers and caused QEMU "Failed to initialize PW context" errors.

Fixes #1838

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have performed a self-review of my code

[cubic-dev-ai]

1 issue found across 1 file

Confidence score: 4/5

• This PR looks safe to merge overall; the main concern is a single medium‑severity check around PulseAudio configuration handling.
• In quickemu, the -S check can reject valid PULSE_SERVER values (e.g., unix:/path or tcp:host:port), which may cause an unnecessary ALSA fallback for users relying on custom PulseAudio servers.
• Pay close attention to quickemu - ensure PULSE_SERVER string values are honored even when they are not filesystem sockets.

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="quickemu">

<violation number="1" location="quickemu:1278">
P2: `PULSE_SERVER` can be a server string (e.g., `unix:/path` or `tcp:host:port`), so the `-S` check will fail for valid PulseAudio configurations and force an ALSA fallback. Consider honoring `PULSE_SERVER` when set and only socket-checking the `unix:` variant.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P2: PULSE_SERVER can be a server string (e.g., unix:/path or tcp:host:port), so the -S check will fail for valid PulseAudio configurations and force an ALSA fallback. Consider honoring PULSE_SERVER when set and only socket-checking the unix: variant.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At quickemu, line 1278:

<comment>`PULSE_SERVER` can be a server string (e.g., `unix:/path` or `tcp:host:port`), so the `-S` check will fail for valid PulseAudio configurations and force an ALSA fallback. Consider honoring `PULSE_SERVER` when set and only socket-checking the `unix:` variant.</comment>

<file context>
@@ -1266,15 +1266,17 @@ function check_cocoa_gl_es_support() {
-    elif ! pidof pulseaudio >/dev/null 2>&1; then
-        AUDIO_DRIVER="alsa"
+        AUDIO_DRIVER="pipewire"
+    elif [ -S "${pa_socket}" ]; then
+        AUDIO_DRIVER="pa"
     fi
</file context>