fresnel-fourier iter3 Phase 6 commit D: buffer.c whitelist for

VAProbabilityBufferType

Phase 2 source-read assumed buffer.c was type-agnostic ("the buffer
registry is type-agnostic" per phase2_iter3_situation.md non-bugs
list). FALSE. RequestCreateBuffer at buffer.c:59-70 has an explicit
allow-list switch:

  case VAPictureParameterBufferType:
  case VAIQMatrixBufferType:
  case VASliceParameterBufferType:
  case VASliceDataBufferType:
  case VAImageBufferType:
      break;
  default:
      return VA_STATUS_ERROR_UNSUPPORTED_BUFFERTYPE;

Without VAProbabilityBufferType in the allow-list, the consumer gets
VA_STATUS_ERROR_UNSUPPORTED_BUFFERTYPE on vaCreateBuffer for the
probability buffer, BEFORE codec_store_buffer is ever reached.
ffmpeg-vaapi log:

  [vp8] Failed to create parameter buffer (type 13): 15
        (the requested VABufferType is not supported).

Same iter1 Commit D pattern: Phase 2 grep didn't find this, runtime
enumerated authoritatively. Per memory feedback_header_deletion_
check.md ("let the compiler enumerate them") — but extended here:
runtime enumerates allow-list violations the same way the compiler
enumerates include-site violations.

Fix: add `case VAProbabilityBufferType:` to the buffer.c allow-list.
+1 line, mechanical.

Refs:
  ../fresnel-fourier/phase2_iter3_situation.md (incorrect non-bug
                                                 claim about buffer.c)
  ../fresnel-fourier/phase4_iter3_plan.md (Commit D placeholder for
                                            fix-forward — used)

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

src/buffer.c

@@ -62,6 +62,7 @@ VAStatus RequestCreateBuffer(VADriverContextP context, VAContextID context_id,
 	case VASliceParameterBufferType:
 	case VASliceDataBufferType:
 	case VAImageBufferType:
+	case VAProbabilityBufferType:
 		break;
 
 	default: