Wayland: VAAPI H.264 + in-process HTTP server, drop ffmpeg

The previous ffmpeg-as-HTTP-server pipeline shape held back two
improvements at once. ffmpeg as the runtime server lost a one-shot
`-listen 1` accept to a probe-and-discard health check, and forced
us to size analyze/probe budgets carefully so ffmpeg would serve
before our deadline. Replacing it with a small tokio task that
accepts once, drains the HTTP request, writes a fixed 200 OK, then
`tokio::io::copy`s gst stdout to the socket removes all of that.

VAAPI H.264 (vah264enc) drops CPU encode from ~50% of a core to
single-digit %. An earlier attempt at vaav1enc had to be abandoned:
libavformat cannot demux AV1-in-MPEG-TS with the custom mapping
even with a 20MB probe budget — mpv reports video=eof. H.264 keeps
the hardware win on the well-trodden demuxer path.

scripts/smoke-pipeline.sh mirrors the runtime pipeline with
videotestsrc/audiotestsrc into a file and asserts that mpv reports
`video=playing` (not video=eof). The naive --frames=10 check was
a false positive when no video stream is recognized; the verbose
grep is the real gate.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/smoke-pipeline.sh

@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+# Pipeline-only smoke test: mirrors host/wayland.rs's gst pipeline but
+# substitutes videotestsrc/audiotestsrc for pipewiresrc/pulsesrc and writes
+# to a file instead of fdsink, so it runs without the portal/PipeWire and
+# without an HTTP/iroh client. Catches AV1 encode + mpegtsmux + AAC mux
+# regressions in ~5 seconds without any user interaction.
+#
+# Usage: scripts/smoke-pipeline.sh
+# Exits 0 on pass, non-zero with diagnostic on fail.
+
+set -euo pipefail
+
+OUT="${TMPDIR:-/tmp}/pixelpass-smoke-$$.ts"
+trap 'rm -f "$OUT"' EXIT
+
+echo "[smoke] running gst pipeline (videotestsrc + audiotestsrc, ~2s) -> $OUT"
+gst-launch-1.0 -q \
+    mpegtsmux name=mux \
+        ! queue ! filesink location="$OUT" \
+    videotestsrc num-buffers=60 is-live=false \
+        ! video/x-raw,width=640,height=360,framerate=30/1 \
+        ! videoconvert ! video/x-raw,format=NV12 \
+        ! vah264enc rate-control=cbr bitrate=2000 key-int-max=60 \
+        ! h264parse config-interval=-1 \
+        ! video/x-h264,stream-format=byte-stream,alignment=au \
+        ! mux. \
+    audiotestsrc num-buffers=94 is-live=false \
+        ! audioconvert ! audioresample \
+        ! audio/x-raw,rate=48000,channels=2 \
+        ! avenc_aac bitrate=128000 ! aacparse ! mux.
+
+[[ -s "$OUT" ]] || { echo "[smoke] FAIL: output file empty or missing"; exit 1; }
+echo "[smoke] output size: $(stat -c %s "$OUT") bytes"
+
+echo "[smoke] ffprobe stream listing"
+ffprobe -v error -show_entries stream=index,codec_type,codec_name "$OUT" \
+    | sed 's/^/        /'
+
+# Real gate: mpv must actually decode video. The previous --frames=10 check was
+# a false positive — if there's no video stream, --frames silently does nothing
+# and mpv exits 0 after playing the audio. We instead grep mpv -v output for
+# "video=playing"; "video=eof" means mpv saw no video track.
+echo "[smoke] mpv video-decode probe (-v, asserting 'video=playing')"
+MPV_LOG=$(mpv --no-config -v --vo=null --ao=null --frames=10 "$OUT" 2>&1)
+echo "$MPV_LOG" | grep -E 'video=(playing|eof)' | sed 's/^/        /'
+if echo "$MPV_LOG" | grep -q 'video=playing'; then
+    echo "[smoke] PASS — pipeline produces an mpv-decodable video + audio stream"
+else
+    echo "[smoke] FAIL: mpv did not decode video (saw video=eof or no video state)"
+    echo "[smoke] last 30 lines of mpv output:"
+    echo "$MPV_LOG" | tail -30 | sed 's/^/        /'
+    exit 1
+fi