fix(host/serverinfo): don't advertise an empty codec mask when the VAAPI probe finds nothing

The Phase 3 GPU-aware codec mask (6922e1c) probes VAAPI on any non-NVIDIA host.
On a GPU-less box (CI container: no /dev/nvidia* -> `auto` picks VAAPI, but there's
no VA display) the probe returns all-false, so the mask was 0 -- the host
advertised NO codecs, and the serverinfo unit test failed.

Fall back to the static superset when the probe yields nothing (VAAPI wasn't
usable, not "the GPU encodes nothing"); quiet ffmpeg's expected "No VA display"
error during the probe; and assert the test against codec_mode_support() rather
than a hardcoded 65793 so it's deterministic regardless of the build host's GPU.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/punktfunk-host/src/encode/vaapi.rs

@@ -134,11 +134,19 @@ pub fn probe_can_encode(codec: Codec) -> bool {
         return false;
     }
     unsafe {
-        let hw = match VaapiHw::new(ffi::AVPixelFormat::AV_PIX_FMT_NV12, 640, 480, 2) {
+        // A missing VA device (non-VAAPI host, GPU-less CI) is an expected probe outcome — quiet
-            Ok(hw) => hw,
+        // ffmpeg's "No VA display found" error for the probe, then restore the level.
-            Err(_) => return false,
+        let prev = ffi::av_log_get_level();
+        ffi::av_log_set_level(ffi::AV_LOG_FATAL);
+        let ok = match VaapiHw::new(ffi::AVPixelFormat::AV_PIX_FMT_NV12, 640, 480, 2) {
+            Ok(hw) => {
+                open_vaapi_encoder(codec, 640, 480, 30, 2_000_000, hw.device_ref, hw.frames_ref)
+                    .is_ok()
+            }
+            Err(_) => false,
         };
-        open_vaapi_encoder(codec, 640, 480, 30, 2_000_000, hw.device_ref, hw.frames_ref).is_ok()
+        ffi::av_log_set_level(prev);
+        ok
     }
 }
 

crates/punktfunk-host/src/gamestream/serverinfo.rs

@@ -61,7 +61,13 @@ fn codec_mode_support() -> u32 {
         if caps.av1 {
             m |= SCM_AV1_MAIN8;
         }
-        return m;
+        // Only trust a probe that actually found an encoder. An empty result means VAAPI wasn't
+        // usable at probe time (no VA display — a GPU-less CI box, or a misconfigured host), NOT
+        // that the GPU encodes nothing; advertise the static superset (pre-probe behaviour) rather
+        // than claiming zero codecs.
+        if m != 0 {
+            return m;
+        }
     }
     SERVER_CODEC_MODE_SUPPORT
 }
@@ -99,6 +105,13 @@ mod tests {
             https_port: 47984,
         };
         let xml = serverinfo_xml(&host, false);
-        assert!(xml.contains("<ServerCodecModeSupport>65793</ServerCodecModeSupport>"));
+        // The mask is the GPU-aware value (NVENC/no-GPU → the static 65793; a VAAPI host →
+        // whatever it probes). Assert the XML embeds exactly what `codec_mode_support()` returns,
+        // so the test is deterministic regardless of the build host's GPU.
+        let mask = codec_mode_support();
+        assert!(mask != 0, "must advertise at least one codec");
+        assert!(xml.contains(&format!(
+            "<ServerCodecModeSupport>{mask}</ServerCodecModeSupport>"
+        )));
     }
 }