ampere-av1 Phase 3: SEQUENCE byte-equal kdirect; 3/10 frames PASS bit-exact

Three more fixes after strace-diff localization vs kdirect.

Fix 6 — fill_sequence ENABLE_SUPERRES: gate on
picture->pic_info_fields.bits.use_superres instead of unconditional
set-true. VAAPI doesn't expose enable_superres at sequence level; per
strace diff kdirect clears the flag for streams not using superres
(byte 1 of flags was the only SEQUENCE diff). After this fix,
SEQUENCE ctrl byte-equal kdirect on every call.

Fix 7 — refresh_frame_flags = 0xff (was 0): VAAPI doesn't expose
refresh_frame_flags. Default 0xff = "refresh all DPB slots" matches
kdirect's submission and AV1 spec default for KEY/SWITCH frames; for
inter frames simple P-frame chains naturally tolerate this.

Fix 8 — surface_object->av1_order_hint per-surface tracking. Set in
av1_set_controls from picture->order_hint of the current frame. Also
propagated to the linked display surface (when apply_grain=1 →
cur_frame != cur_display) so future frames referencing the display
surface find the order_hint via the linked_decode_surface_id.

Tried + reverted: ref-name iteration of reference_frame_ts / order_hints
via picture->ref_frame_idx[i-1] → DPB slot (Kwiboo's convention via
FFmpeg's s->ref[i]). Empirically regressed 3/10 → 1/10. V4L2 uAPI's
indexing here looks DPB-slot-direct despite the AV1 spec lexicon —
needs kernel-side disambiguation to settle.

Verification on ampere (av1_larger.ivf 352x288, 10 frames):
  Frames 0, 2, 4: PASS bit-exact (apply_grain=1, grain HW path)
  Frames 1, 3, 5-9: DIFF (apply_grain=0)
  3/10 PASS (was 1/10 after iter checkpoint).
  test_av1.ivf 208x208: unchanged bit-exact PASS sha 029ee72c214b37c1

Remaining open: frame 1 (apply_grain=0, first inter) submits IDENTICAL
FRAME ctrl bytes to kdirect (verified strace-diff post-fix), yet
decoded output diverges. That means the divergence is no longer in
control submission — points at OUTPUT-side bitstream differences
between ffmpeg-vaapi and ffmpeg-v4l2request, or at DPB CAPTURE buffer
state (grain-applied data being used as reference vs pre-grain).

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

src/surface.h

@@ -106,6 +106,16 @@ struct object_surface {
 	 */
 	VASurfaceID linked_decode_surface_id;
 
+	/*
+	 * AV1 Phase 3: AV1 order_hint of the frame currently decoded into
+	 * this surface. VAAPI's VADecPictureParameterBufferAV1.order_hint
+	 * is per-frame; kernel's v4l2_ctrl_av1_frame.order_hints[8] is
+	 * per-reference. We track each decoded frame's order_hint here so
+	 * the next frame's av1_set_controls can populate order_hints[i]
+	 * from ref_frame_map[i] → SURFACE → av1_order_hint.
+	 */
+	uint8_t av1_order_hint;
+
 	union {
 		struct {
 			VAPictureParameterBufferMPEG2 picture;