fresnel-fourier iter4 Phase 6 commit B: NEW src/vp9.c + src/vp9.h + meson.build + context.h (vp9_lf) + surface.h (params.vp9)

VP9 codec dispatcher implementing 12 contract clauses against
V4L2_CID_STATELESS_VP9_FRAME (0xa40a2c) +
V4L2_CID_STATELESS_VP9_COMPRESSED_HDR (0xa40a2d). 2 batched
controls per frame; rkvdec on RK3399 mandatorily requires both
per drivers/staging/media/rkvdec/rkvdec-vp9.c::rkvdec_vp9_run_preamble:752.

Implementation:
- ~80 LOC VPX range coder (vp9_rac_*) — minimal port of FFmpeg
  vpx_rac.[ch] + vp89_rac.h. Stateless static helpers.
- inv_map_table[255] + read_prob_delta — verbatim copy from
  v4l2_request_vp9.c:44-97.
- vp9_parse_uncompressed_header_lf_quant — partial parse for the
  fields VAAPI doesn't expose: lf_delta_enabled / lf_delta_update /
  lf_ref_delta[4] / lf_mode_delta[2] / base_q_idx /
  delta_q_y_dc / delta_q_uv_dc / delta_q_uv_ac. ~120 LOC.
- vp9_fill_compressed_hdr — port of FFmpeg fill_compressed_hdr
  with Phase 5 C3 out_reference_mode parameter. ~140 LOC.
- vp9_set_controls — orchestrates Clauses 1+2+4+5+7+10+11+12.
  ~120 LOC.

Phase 5 amendments incorporated in code:
- C1: frame.interpolation_filter = direct from VAAPI's
  mcomp_filter_type (NO XOR; vaapi_vp9.c:62 already applied it
  before storing into VAAPI's mcomp_filter_type).
- C2: persistent vp9_lf state added to object_context (in
  context.h). Initialized to VP9 spec defaults
  {1,0,-1,-1,0,0} on keyframe / intra_only / error_resilient.
  Updated only when parser sees lf_delta.update=1. Always
  copied to kernel control.
- C3: vp9_fill_compressed_hdr takes uint8_t *out_reference_mode;
  threaded through call site. allowcompinter derived from VAAPI
  sign-bias bits.

Phase 5 S4: uv_mode memcpy from FFmpeg's fill_compressed_hdr
omitted — rkvdec reads uv_mode from kernel's persistent
probability_tables, NOT from prob_updates ctrl.

Clause 3 compile-time _Static_assert on struct sizes (168/2040)
matches Phase 3 empirical baseline; UAPI shifts will fail loudly.

surface.h: extends params union with vp9 { picture, slice }.
context.h: adds vp9_lf { ref_deltas[4], mode_deltas[2], initialized }.
meson.build: adds vp9.c + vp9.h.

Build: clean on fresnel (linux-fresnel-fourier 7.0-1, libva 1.23).
Runtime: not yet wired in picture.c — next commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/meson.build

@@ -48,7 +48,8 @@ sources = [
 	'request_pool.c',
 	'cap_pool.c',
 	'h265.c',
-	'vp8.c'
+	'vp8.c',
+	'vp9.c'
 ]
 
 headers = [
@@ -72,7 +73,8 @@ headers = [
 	'request_pool.h',
 	'cap_pool.h',
 	'h265.h',
-	'vp8.h'
+	'vp8.h',
+	'vp9.h'
 ]
 
 includes = [