ffmpeg-v4l2-request-fourier: substitute H.264 luma-v deblock → daedalus-fourier

Cycle 8 of the libavcodec.so substitution arc (reauktion/daedalus-v4l2#11
step 2).  H264DSPContext.v_loop_filter_luma — non-intra bS<4 vertical
luma deblock, called per macroblock-row edge from the slice deblock
loop in libavcodec/h264_loopfilter.c — now dispatches through
daedalus_recipe_dispatch_h264_deblock_luma_v instead of
ff_h264_v_loop_filter_luma_neon.

## What

- Add 0005-h264-deblock-luma-v-daedalus-fourier.patch (in both arch/
  and debian/ ffmpeg-v4l2-request-fourier/).  Extends
  libavcodec/aarch64/h264_idct_daedalus.c with
  ff_h264_v_loop_filter_luma_daedalus (constructs a
  daedalus_h264_deblock_meta from FFmpeg's (alpha, beta, tc0[4]) and
  calls daedalus_recipe_dispatch_h264_deblock_luma_v with n_edges=1).
  Patches libavcodec/aarch64/h264dsp_init_aarch64.c to wire
  c->v_loop_filter_luma to the new shim.
- arch/PKGBUILD + debian/build-deb.sh: append patch + bump pkgrel/PKGREL
  to 8.
- No new build-deps, no Depends change, no daedalus-fourier rev — the
  d87239d pin already exposes daedalus_recipe_dispatch_h264_deblock_luma_v.

## Why

Cycle 8 is marked "CPU primary; QPU opportunistic" in the daedalus-
fourier API docstring.  Per the hybrid substrate philosophy
("if there's a coprocessor, use it") we eventually want the QPU
opportunism active here.  But the libavcodec.so context is
process-global and shared with cycles 6/7 via pthread_once, and it
uses daedalus_ctx_create_no_qpu deliberately to avoid implicit
Vulkan init in arbitrary host processes (Firefox content, mpv-fourier,
ffmpeg-fourier CLI, ...).  Switching to daedalus_ctx_create here
without a feature flag would be a footgun.

So cycle 8 lands as plumbing-only NEON-by-recipe substitution for
now; opportunistic QPU enablement is a separate follow-up that adds
a DAEDALUS_FOURIER_ENABLE_QPU env var or equivalent.

## Scope NOT covered

- Intra (bS=4) loop filter c->v_loop_filter_luma_intra — daedalus's
  daedalus_h264_deblock_meta only covers the non-intra path.
- Horizontal-edge variant c->h_loop_filter_luma — separate kernel
  (not yet in daedalus-fourier API).
- Chroma loop filters — separate kernels.
- Bulk batching — single-edge dispatch wastes the kernel's n_edges>1
  amortization.  Same caveat as cycles 6/7; follow-up.
- QPU opportunism — see "Why" above.

## SONAME

Unchanged.  libavcodec.so.62 / libavformat.so.62 / libavutil.so.60.

## Refs

- reauktion/daedalus-v4l2 issue #11: reauktion/daedalus-v4l2#11
- marfrit-packages PR #76 (cycle 6 IDCT 4×4)
- marfrit-packages PR #85 (cycle 7 IDCT 8×8)
- marfrit/daedalus-fourier cycle 8 close (deblock luma-v NEON green)

debian/ffmpeg-v4l2-request-fourier/build-deb.sh

@@ -33,11 +33,13 @@ FFMPEG_VERSION=8.1
 # epoch 2 matches Debian's stock ffmpeg (currently 7:7.1.x in trixie);
 # +rfourier suffix to avoid colliding with upstream/Debian rebuilds.
 PKGVER=2:${FFMPEG_VERSION}+rfourier+gb57fbbe
-PKGREL=7  # pkgrel=7 — H.264 IDCT 8x8 daedalus-fourier substitution
-          # (cycle 7).  Stacks on top of cycle-6 IDCT 4x4 (PR #76) and
-          # the libxml2-drop ABI-skew workaround (PR #78).  Wires
-          # H264DSPContext.idct8_add through
-          # daedalus_recipe_dispatch_h264_idct8.  (2026-05-22)
+PKGREL=8  # pkgrel=8 — H.264 luma-v deblock daedalus-fourier substitution
+          # (cycle 8, non-intra bS<4 vertical luma).  Stacks on cycles
+          # 6/7 (IDCT 4x4 + 8x8).  Wires H264DSPContext.v_loop_filter_luma
+          # through daedalus_recipe_dispatch_h264_deblock_luma_v.
+          # ctx stays no-QPU until a separate change gates Vulkan init
+          # on a feature flag; cycle-8 dispatch is NEON-by-recipe for
+          # now.  (2026-05-22)
 
 # daedalus-fourier pin — first kernel substitution in libavcodec (cycle 6
 # H.264 IDCT 4x4).  Same SHA as the daedalus-v4l2 daemon already ships
@@ -68,6 +70,7 @@ patch -Np1 -i "$HERE/0001-libudev-bypass-fallback.patch"
 patch -Np1 -i "$HERE/0002-nv15-to-p010-unpack.patch"
 patch -Np1 -i "$HERE/0003-h264-idct4-daedalus-fourier.patch"
 patch -Np1 -i "$HERE/0004-h264-idct8-daedalus-fourier.patch"
+patch -Np1 -i "$HERE/0005-h264-deblock-luma-v-daedalus-fourier.patch"
 
 # --- daedalus-fourier: fetch + build static .a with PIC, install to a
 # per-build prefix; libavcodec.so links it into the shared object so