diff --git a/PRE_COMPACT_HANDOFF.md b/PRE_COMPACT_HANDOFF.md
index 46786a8..03be653 100644
--- a/PRE_COMPACT_HANDOFF.md
+++ b/PRE_COMPACT_HANDOFF.md
@@ -1,6 +1,6 @@
-# Pre-Compact Handoff — Session 2026-05-14 (FINAL post iter38)
+# Pre-Compact Handoff — Session 2026-05-17 (iter39 sub-profile work landed, pending fresnel test)
 
-Use this doc to resume the fresnel-fourier campaign after Claude context compaction. **Campaign at definitive close: 5/5 codecs PASS in a single libva session, no env-override required.**
+Use this doc to resume the fresnel-fourier campaign after Claude context compaction. **Iter38 close still holds (5/5 PASS, single libva session). Iter39 sub-profile work (H264 Hi10P + HEVC Main10) committed at backend `662f887` and awaiting Phase 7 validation on fresnel.**
 
 ## TL;DR
 
@@ -14,6 +14,7 @@ Use this doc to resume the fresnel-fourier campaign after Claude context compact
 | Env-gated DIAG probes (iter29/30/33/35) | **CLEANED** | iter36 (-131 / +7 LOC) |
 | α-26 mis-routed cosmetic | **REVERTED** | iter37 (1-line; rkvdec never read that field) |
 | Libva multi-device probe | **DONE** | iter38 (single session serves all 5 codecs; no env override needed) |
+| H264 Hi10P + HEVC Main10 sub-profile | **CODE LANDED — Phase 7 PENDING** | iter39 α-31 (backend 662f887): NV15 CAPTURE pix_fmt, synthetic-SPS bit_depth=2, NV15→P010 userspace unpack in copy_surface_to_image, P010 reporting in DeriveImage/QueryImageFormats. Self-tested (test_nv15_unpack passes on noether). Awaiting fresnel power-on for vainfo enumeration + libva.P010==kdirect.P010 bit-exact verification. |
 
 | Codec | libva 10F sha | kdirect 10F sha | SW 10F sha | L==K | L==SW |
 |---|---|---|---|---|---|
@@ -48,7 +49,7 @@ vainfo: Supported profile and entrypoints
 | Component | Location | Tip |
 |---|---|---|
 | Campaign repo (this) | `/home/mfritsche/src/fresnel-fourier/` | `ba4b6fd` on gitea master |
-| Libva backend fork (noether) | `/home/mfritsche/src/libva-multiplanar/libva-v4l2-request-fourier/` | `7ac934e` on gitea master |
+| Libva backend fork (noether) | `/home/mfritsche/src/libva-multiplanar/libva-v4l2-request-fourier/` | `662f887` on gitea master (iter39 α-31; iter38b is `7ac934e`) |
 | Libva backend (fresnel deploy) | `/home/mfritsche/src/libva-v4l2-request-fourier/` | sync to gitea master, `ninja -C build` |
 | Kernel source (boltzmann) | `~/src/kernel-agent-bootstrap/build/marfrit-packages/arch/linux-fresnel-fourier/` | pkgrel=14 clean |
 | Kernel running on fresnel | `linux-fresnel-fourier 7.0-14` | clean shipping kernel, no diagnostic printks |
@@ -153,7 +154,42 @@ Expect: 5× PASS.
 
 1. **Multi-context simultaneously** — current design supports only one decode context at a time across devices (device switch tears down pools). Could be expanded to per-context pools to support simultaneous mixed-codec decode. Not requested.
 
-2. **Sub-profile support** — H264 Hi10P, HEVC Main10, VP9 Profile 2 are HW-supported on RK3399 but the libva backend has no entries in `pixelformat_for_profile` and elsewhere. Out of scope for this campaign.
+2. ~~**Sub-profile support**~~ — *Phase 6 LANDED 2026-05-17 (iter39 α-31, backend `662f887`)*. H264 Hi10P + HEVC Main10 wired through the backend with NV15→P010 userspace unpack. VP9 Profile 2 explicitly excluded (RK3399 rkvdec kernel ctrl caps at PROFILE_0). PRIME-side P010 emission deferred (consumers wanting P010 must use the COPY path). Phase 7 test rig at `phase7_iter39_test_rig.sh`; awaiting fresnel.
+
+## Resumption sequence — iter39 Phase 7 (when fresnel is up)
+
+```bash
+# 1. Sync + build backend on fresnel
+ssh fresnel 'cd ~/src/libva-v4l2-request-fourier && \
+    git fetch && git reset --hard origin/master && \
+    ninja -C build && \
+    sudo install -m644 build/src/v4l2_request_drv_video.so /usr/lib/dri/'
+
+# 2. Push test rig + run
+scp ~/src/fresnel-fourier/phase7_iter39_test_rig.sh fresnel:/tmp/
+ssh fresnel 'bash /tmp/phase7_iter39_test_rig.sh'
+
+# Expected pass criteria:
+#   1. vainfo lists VAProfileH264High10 + VAProfileHEVCMain10
+#   2. libva.P010 SHA == kdirect.P010 SHA for Hi10P and Main10 fixtures
+#      (both paths use -vf hwdownload,format=p010le to normalize NV15)
+#   3. SSIM_Y vs libavcodec SW (yuv420p10le) >= 0.999
+#   4. iter38 5/5 PASS baseline still holds on H264/HEVC/VP9/VP8/MPEG-2
+```
+
+## Iter39 internals — pre-Phase 7 verification done
+
+- **Self-test** of `nv15_unpack_plane_to_p010` (`tests/test_nv15_unpack.c` in backend): zero / all-max / 8 known vectors / remainder widths {1,2,3,7} / multi-row stride-padding / chroma-shape — ALL PASS on noether x86_64.
+- **Compile-test**: aarch64 native build on boltzmann clean (gcc 15.2.1 / libva 1.23.0 / libdrm 2.4.133), .so produced, 0 new warnings.
+- **Self-review of commit 662f887** vs Phase 5 amendments: APPROVED. All 3 mandatory amendments + MAX_PROFILES bump + guard updates + NV15-stride source confirmed present.
+
+## Iter39 design notes (load-bearing)
+
+- `driver_data->is_10bit` is the per-session flag (request.h). Set in `RequestCreateContext` from `config_object->profile`, cleared in `RequestDestroyContext`. Drives image.c P010 reporting/unpack and context.c CAPTURE pix_fmt.
+- `video_format` cache invalidated on bit-depth transition (sibling to iter38's device-switch invalidation in `request_switch_device_for_profile`). Same session can now alternate Main → Main10 contexts.
+- Synthetic SPS pre-seed (α-25 lineage) extended for 10-bit: `bit_depth_luma_minus8 = 2`. Image_fmt resolution in `rkvdec-h264-common.c:196` + `rkvdec-hevc-common.c:467` dispatches on bit_depth_luma_minus8 only — profile_idc ignored, `v4l2_ctrl_hevc_sps` has no profile_idc field at all.
+- NV15 stride = V4L2-reported `destination_bytesperlines[i]` (kernel may pad above `ceil(width/4)*5`). NEVER assume `width*2`.
+- VP9 Profile 2 NOT in any path. Added comment in config.c near VAProfileVP9Profile0 case to deter future "completeness" PRs.
 
 ## Memory entries (full campaign set)
 
diff --git a/phase4_iter39_subprofile_plan.md b/phase4_iter39_subprofile_plan.md
new file mode 100644
index 0000000..54b2468
--- /dev/null
+++ b/phase4_iter39_subprofile_plan.md
@@ -0,0 +1,125 @@
+# Phase 4 — iter39 sub-profile support plan
+
+**Status:** Phase 6 LANDED at backend `662f887` on gitea master (pushed 2026-05-17).
+Phase 5 review (sonnet-architect, 3 mandatory amendments + 1 corrected claim) folded in below.
+Phase 7 test rig at `phase7_iter39_test_rig.sh`; blocked on fresnel power-on.
+
+
+
+## FR
+
+PRE_COMPACT_HANDOFF.md "Open items" #2 — H264 Hi10P, HEVC Main10, VP9 Profile 2 are advertised as HW-capable on RK3399 but the libva backend has no entries. Drop them in.
+
+## Phase 0/2 findings (locked from linux-mmind-v7.0 rkvdec source on boltzmann)
+
+`drivers/media/platform/rockchip/rkvdec/rkvdec.c` ctrl tables, with `rk3399_rkvdec_variant` binding `rkvdec_coded_fmts`:
+
+| VAProfile         | rkvdec HW | V4L2 OUTPUT pix_fmt   | rkvdec CAPTURE pix_fmt | notes |
+|-------------------|-----------|------------------------|------------------------|-------|
+| `H264High10`      | ✅ yes    | `H264_SLICE`           | `NV15` (4:2:0 10-bit)  | ctrl `cfg.max=HIGH_422_INTRA`, `bit_depth_luma_minus8==2` path live in `rkvdec-h264-common.c:196` |
+| `HEVCMain10`      | ✅ yes    | `HEVC_SLICE`           | `NV15`                 | ctrl `cfg.max=MAIN_10`, rkvdec-hevc.c:514 "only 8-bit and 10-bit are supported" |
+| `VP9Profile2`     | ❌ no     | n/a                    | n/a                    | rkvdec-vp9.c:670 "We only support profile 0"; ctrl `cfg.max=PROFILE_0`. **EXCLUDED FROM SCOPE.** |
+
+Bonus / aside: H264 4:2:2 profiles also supported by HW (NV16/NV20) but VAAPI's `VAProfileH264High422` is non-standard and most consumers won't use it. **OUT OF SCOPE.**
+
+## Architectural ripple — NV15 ↔ VA-standard pixel format
+
+The hard part. RK3399 rkvdec emits 10-bit frames as **NV15**: 4 × 10-bit values packed in 5 bytes per element, no padding. VAAPI's standard 10-bit fourcc is **P010**: 2 bytes per pixel, 10 high bits used, 6 low bits zero. Mapping requires a bit unpack pass.
+
+`/usr/include/va/va.h`:
+- `VA_FOURCC_P010 = 0x30313050` (defined, standard)
+- `VA_FOURCC_NV15` (not defined — would need inline `VA_FOURCC('N','V','1','5')`)
+- `VA_RT_FORMAT_YUV420_10 = 0x100` (defined)
+
+ffmpeg-v4l2-request kdirect path already handles NV15 → P010 internally inside `libavcodec/v4l2_request_hevc.c` family for the kdirect-test-rig codepath — so kdirect output for a Main10 fixture lands in P010 buffers already. Our libva-vs-kdirect bit-exact contract can still hold if we surface P010 too.
+
+### Three scope options
+
+**Option A — Enumerate-only.** Wire profile lists, pixelformat_for_profile, picture.c, synthetic SPS bit_depth. Skip the unpack. vainfo will list Hi10P / Main10 but actual decode emits NV15 in raw buffers that no standard VAAPI consumer understands. Misleading — not recommended.
+
+**Option B — NV15-as-FOURCC expose.** Surface decoded NV15 with a non-standard `VA_FOURCC('N','V','1','5')`. Mesa/ffmpeg-vaapi will reject in their `vaCreateImage` path. Only useful for `vaExportSurfaceHandle` (DRM-PRIME) consumers that understand DRM_FORMAT_NV15 modifiers — Mesa panfrost-Midgard support unclear.
+
+**Option C — Userspace unpack to P010.** Add `nv15_to_p010()` in surface.c / image.c, run in `copy_surface_to_image`. ~150 LOC bit-twiddling. Adds 1× decoded-frame-size memcpy + bit unpack per `vaDeriveImage` / `vaGetImage` call. Standard VAAPI consumers work as expected.
+
+**Option D — Skeleton only / documented partial.** Profiles enumerated, decode goes through, but `vaDeriveImage` returns `VA_STATUS_ERROR_UNIMPLEMENTED` for 10-bit surfaces with a clear log. Real downstream usage broken; flagged as known limitation in README + memory.
+
+## Recommended plan: Option C (full P010 unpack) — LOCKED
+
+Reasoning: PRE_COMPACT_HANDOFF.md marks this as "open polish item" — partial-work options A/B/D would resurface as a TODO. Sub-profile support is only useful end-to-end. Option C is the only one that lets a Main10 fixture round-trip through `ffmpeg -hwaccel vaapi -i x.hevc.10b.mp4 ...` with our backend.
+
+NV15 packing per `Documentation/userspace-api/media/v4l/pixfmt-nv15.rst` (linux-mmind-v7.0): 4×10-bit values packed in 5 consecutive bytes — `A[9:2] A[1:0]B[9:4] B[3:0]C[7:6] C[5:0]D[9:8] D[7:0]`. Unpack one 5-byte group → 4 P010 words (2B each, value in bits [15:6], zeros in [5:0]).
+
+**Stride gotcha (per Phase 5 review)**: NV15 row stride is `ceil(width/4)*5` bytes, NOT `width*2`. The kernel's `G_FMT` returns the NV15 stride in `destination_bytesperlines[0]`. The unpack must use NV15 stride for source iteration and compute P010 stride independently as `width * 2`.
+
+**kdirect does NOT unpack (Phase 5 correction)**: ffmpeg-v4l2-request's hwcontext_v4l2request.c maps NV15 as `AV_PIX_FMT_YUV420P10` with `DRM_FORMAT_NV15` modifier and exports raw DRM_PRIME. The downstream `av_frame_copy` uses libswscale's unpack — kdirect itself emits raw NV15 in DRM-PRIME buffers. **The libva backend cannot use that trick** — `vaGetImage` consumers receive a `VAImage` buffer (no AVFrame, no libswscale call). The Option C userspace unpack is the only path.
+
+## Code changes (Option C, amended after Phase 5 review)
+
+### libva-v4l2-request-fourier (gitea master, claude-noether identity)
+
+**src/codec.c** — `pixelformat_for_profile`:
+- Add `case VAProfileH264High10:` → `V4L2_PIX_FMT_H264_SLICE` (same OUTPUT slice as 8-bit H.264 — bit depth is signaled via SPS contents not OUTPUT pix_fmt)
+- Add `case VAProfileHEVCMain10:` → `V4L2_PIX_FMT_HEVC_SLICE`
+
+**src/config.c**:
+- `RequestCreateConfig` switch: add the 2 profile cases (no-op validation, same shape as siblings)
+- `RequestQueryConfigProfiles`: append `VAProfileH264High10` after existing H264 block (guard `-5` → `-6`), `VAProfileHEVCMain10` after `HEVCMain` (guard `-1` → `-2`). Bump `V4L2_REQUEST_MAX_PROFILES` from 11 → 13 in `request.h`.
+- `RequestQueryConfigEntrypoints`: add the 2 profile cases
+- `RequestGetConfigAttributes` + the inline assignment in `RequestCreateConfig` (line 122): branch on profile to return `VA_RT_FORMAT_YUV420_10` instead of `VA_RT_FORMAT_YUV420` for 10-bit profiles.
+
+**src/context.c** — `RequestCreateContext`:
+- Line 111-131 CAPTURE-probe block: extend to try NV15 first for 10-bit profiles (else NULL `video_format` → NULL-deref at line 135). Profile-gated branch.
+- Line 178 `capture_pixelformat = V4L2_PIX_FMT_NV12` → branch on profile to set `V4L2_PIX_FMT_NV15` for 10-bit profiles.
+- Synthetic SPS (line 235+): add Hi10P / Main10 cases with `bit_depth_luma_minus8 = 2`, `bit_depth_chroma_minus8 = 2`. H264 `profile_idc=110` is benign-but-unnecessary per Phase 5 review (kernel ignores in `get_image_fmt`); HEVC SPS has no profile_idc field at all. Image_fmt resolution is purely on `bit_depth_luma_minus8` (==2) + `chroma_format_idc` (==1).
+
+**src/video.c — CRITICAL (Phase 5 amendment 1)**:
+- `formats[]` table (line 37) currently has only NV12 entry. **Add NV15 entry.** Without this, `video_format_find(V4L2_PIX_FMT_NV15)` at context.c:117 returns NULL → `v4l2_type_video_capture()` at context.c:135 NULL-derefs.
+
+**src/picture.c** — 5 switch blocks (lines 102, 123, 165, 210, 277). Add the new cases routing to the same per-codec function as the 8-bit profile siblings.
+
+**src/h264.c / src/h265.c** — verify `bit_depth_luma_minus8 != 0` paths exist (they do, mapped to V4L2_CTRL field). No change expected.
+
+**src/surface.c — CRITICAL (Phase 5 amendment 2)**:
+- Line 185: `if (format != VA_RT_FORMAT_YUV420) return UNSUPPORTED;` — extend to `(format != YUV420 && format != YUV420_10)`. Without this fix the 10-bit `vaCreateSurfaces` aborts before context creation.
+- `copy_surface_to_image`: branch on surface fourcc — if NV15 source, call unpack into P010 destination
+- `RequestExportSurfaceHandle` (line ~685): emit `DRM_FORMAT_P010` (copy path) or pass-through `DRM_FORMAT_NV15` for PRIME path. Ship copy path only for v1; PRIME path is follow-up.
+
+**src/image.c — CRITICAL (Phase 5 amendment 3)**:
+- `RequestDeriveImage` line ~272: hardcoded `format.fourcc = VA_FOURCC_NV12` + `bits_per_pixel = 12`. **Branch on the underlying surface's bit depth** — emit `VA_FOURCC_P010` + `bits_per_pixel = 24` for 10-bit surfaces.
+- `RequestQueryImageFormats` line ~326: currently advertises NV12 only. Extend to also advertise P010 when the active session is 10-bit. Requires per-session `is_10bit` flag on `driver_data` or a config lookup.
+
+**src/request.h or struct request_data**:
+- Add `bool is_10bit` (or equivalent — could derive from active config), set in `RequestCreateContext` based on `config_object->profile`, used by image.c branches.
+
+**src/nv15.c + src/nv15.h (new files)**:
+- `nv15_to_p010(const uint8_t *src, uint16_t *dst, unsigned int width, unsigned int height, unsigned int src_stride)` — pure C bit unpack. ~30-40 LOC for the function itself. `dst_stride = width * 2` (computed inline). `src_stride = ceil(width/4)*5` from kernel G_FMT.
+- Two calls: luma plane (full size), chroma plane (UV interleaved, half-height).
+
+### Diff size estimate (revised)
+- codec.c, config.c, picture.c, context.c, video.c: ~80 LOC
+- surface.c + image.c branches: ~50 LOC
+- NV15→P010 unpack (nv15.c new): ~50 LOC
+- Total: ~180 LOC (Phase 5 corrected pessimistic 150→100 for unpack itself; offset by extra video.c + image.c + surface.c amendments)
+
+## Test plan (Phase 7)
+
+**Fixtures (acquire on fresnel):**
+```bash
+# Re-encode BBB into Main10 + Hi10P
+ffmpeg -i ~/measurements/source/bbb_720p.mov -t 10 -c:v libx265 -preset fast -crf 28 \
+    -pix_fmt yuv420p10le -profile:v main10 ~/measurements/encoded/bbb_main10.mp4
+ffmpeg -i ~/measurements/source/bbb_720p.mov -t 10 -c:v libx264 -preset medium -crf 23 \
+    -pix_fmt yuv420p10le -profile:v high10 ~/measurements/encoded/bbb_hi10p.mp4
+```
+
+**Criteria:**
+1. `vainfo` lists `VAProfileHEVCMain10` + `VAProfileH264High10`.
+2. `ffmpeg -hwaccel vaapi -i bbb_main10.mp4 -vf hwdownload,format=p010le -frames:v 10 -f rawvideo /tmp/L_main10.yuv` succeeds without error.
+3. SHA matches between libva and kdirect for 10 frames each codec — **using the same `-vf hwdownload,format=p010le` on BOTH paths** (kdirect emits NV15 via DRM-PRIME and libswscale unpacks via the format filter; libva emits P010 directly via our new unpack). The format filter normalizes both into P010 byte stream.
+4. SSIM vs libavcodec SW reference ≥ 0.999 against `-pix_fmt yuv420p10le` SW decode (Main10 SW reference encoded above; convert P010 to YUV420P10 in the compare step or compare SSIM_Y after conversion).
+5. No regression — 5/5 PASS still holds on the existing 5-codec smoke (run after changes).
+
+## Open / pending decisions
+
+- **PRIME path vs copy path for 10-bit**: ship copy-only first (P010 derived/created images), defer PRIME path for a follow-up. Many consumers actually use `vaPutImage` rather than `vaExportSurface` so this covers most cases.
+- **VP9 Profile 2**: confirmed HW-unsupported on RK3399; do NOT add to enumeration. Add an explicit `/* not on RK3399 rkvdec */` comment in config.c near the VP9 line to prevent future "completeness" PRs adding it.
diff --git a/phase7_iter39_test_rig.sh b/phase7_iter39_test_rig.sh
new file mode 100755
index 0000000..317973a
--- /dev/null
+++ b/phase7_iter39_test_rig.sh
@@ -0,0 +1,162 @@
+#!/bin/bash
+#
+# Phase 7 test rig for iter39 sub-profile support (Hi10P + Main10).
+# Run on fresnel after kernel 7.0-14 boot + iter39 backend deploy.
+#
+# Prerequisites on fresnel:
+#   1. linux-fresnel-fourier 7.0-14 booted
+#   2. backend sync + build:
+#        cd ~/src/libva-v4l2-request-fourier
+#        git fetch && git reset --hard origin/master   # → 662f887
+#        ninja -C build
+#        sudo install -m644 build/src/v4l2_request_drv_video.so /usr/lib/dri/
+#   3. Test fixtures (will be encoded by this script if missing):
+#        ~/measurements/encoded/bbb_main10.mp4    (HEVC Main10, 10-bit)
+#        ~/measurements/encoded/bbb_hi10p.mp4     (H.264 Hi10P, 10-bit)
+#
+# Exit code 0 = all criteria PASS.
+
+set -eu
+
+ENCODED_DIR="${ENCODED_DIR:-$HOME/measurements/encoded}"
+SOURCE="${SOURCE:-$HOME/measurements/source/bbb_720p.mov}"
+OUT="${OUT:-/tmp/iter39_test}"
+
+mkdir -p "$ENCODED_DIR" "$OUT"
+
+# Step 1 — encode 10-bit fixtures if missing.
+if [ ! -f "$ENCODED_DIR/bbb_main10.mp4" ]; then
+    echo "==> Encoding HEVC Main10 fixture"
+    ffmpeg -hide_banner -loglevel error -i "$SOURCE" -t 10 \
+        -c:v libx265 -preset fast -crf 28 \
+        -pix_fmt yuv420p10le -profile:v main10 \
+        -tag:v hvc1 "$ENCODED_DIR/bbb_main10.mp4"
+fi
+if [ ! -f "$ENCODED_DIR/bbb_hi10p.mp4" ]; then
+    echo "==> Encoding H.264 Hi10P fixture"
+    ffmpeg -hide_banner -loglevel error -i "$SOURCE" -t 10 \
+        -c:v libx264 -preset medium -crf 23 \
+        -pix_fmt yuv420p10le -profile:v high10 \
+        "$ENCODED_DIR/bbb_hi10p.mp4"
+fi
+
+# Step 2 — vainfo enumeration check.
+echo ""
+echo "==> Criterion 1: vainfo lists VAProfileHEVCMain10 + VAProfileH264High10"
+VAINFO_OUT="$(env LIBVA_DRIVER_NAME=v4l2_request \
+                  LIBVA_DRIVERS_PATH="$HOME/src/libva-v4l2-request-fourier/build/src" \
+                  vainfo 2>&1)"
+echo "$VAINFO_OUT" | grep -E "VAProfile(H264High10|HEVCMain10)" || {
+    echo "FAIL: missing 10-bit profile in vainfo output"
+    echo "$VAINFO_OUT" | grep VAProfile | sed 's/^/  /'
+    exit 1
+}
+echo "  -> PASS"
+
+# Step 3 — per-codec libva-vs-kdirect bit-exactness (Sub-criterion: P010 layout).
+echo ""
+echo "==> Criteria 2-3: libva.P010 == kdirect.P010 for HEVC Main10 + H264 Hi10P"
+
+run_codec() {
+    local name="$1" fixture="$2"
+    echo "  -- $name ($fixture) --"
+
+    # libva path (our iter39 backend, NV15→P010 unpack)
+    env LIBVA_DRIVER_NAME=v4l2_request \
+        LIBVA_DRIVERS_PATH="$HOME/src/libva-v4l2-request-fourier/build/src" \
+        ffmpeg -hide_banner -loglevel error -y \
+        -hwaccel vaapi -hwaccel_output_format vaapi \
+        -i "$ENCODED_DIR/$fixture" \
+        -vf "hwdownload,format=p010le" -frames:v 10 \
+        -f rawvideo -pix_fmt p010le "$OUT/L_${name}.p010" || {
+            echo "    libva path FAIL"; return 1
+        }
+
+    # kdirect path (ffmpeg-v4l2-request hwaccel, libswscale unpacks NV15→YUV420P10)
+    ffmpeg -hide_banner -loglevel error -y \
+        -hwaccel v4l2request -hwaccel_output_format drm_prime \
+        -i "$ENCODED_DIR/$fixture" \
+        -vf "hwdownload,format=p010le" -frames:v 10 \
+        -f rawvideo -pix_fmt p010le "$OUT/K_${name}.p010" || {
+            echo "    kdirect path FAIL"; return 1
+        }
+
+    L_SHA=$(sha256sum "$OUT/L_${name}.p010" | cut -c1-16)
+    K_SHA=$(sha256sum "$OUT/K_${name}.p010" | cut -c1-16)
+    if [ "$L_SHA" = "$K_SHA" ]; then
+        echo "    PASS  libva.P010 == kdirect.P010  sha=$L_SHA"
+        return 0
+    else
+        echo "    FAIL  libva.P010 != kdirect.P010"
+        echo "      libva   sha=$L_SHA"
+        echo "      kdirect sha=$K_SHA"
+        return 1
+    fi
+}
+
+FAIL_COUNT=0
+run_codec hevc_main10 bbb_main10.mp4 || FAIL_COUNT=$((FAIL_COUNT + 1))
+run_codec h264_hi10p  bbb_hi10p.mp4  || FAIL_COUNT=$((FAIL_COUNT + 1))
+
+# Step 4 — SSIM vs SW reference (criterion 4)
+echo ""
+echo "==> Criterion 4: SSIM_Y >= 0.999 vs libavcodec SW (yuv420p10le)"
+
+run_ssim() {
+    local name="$1" fixture="$2"
+    ffmpeg -hide_banner -loglevel error -y \
+        -i "$ENCODED_DIR/$fixture" \
+        -vf "format=yuv420p10le" -frames:v 10 \
+        -f rawvideo -pix_fmt yuv420p10le "$OUT/SW_${name}.yuv" || return 1
+
+    # Compare P010 (libva) to YUV420P10 (SW) using ffmpeg's ssim filter
+    # — feed both as raw with known shape, force same conversion.
+    SSIM=$(ffmpeg -hide_banner -loglevel info \
+        -f rawvideo -pix_fmt p010le -s 1280x720 -i "$OUT/L_${name}.p010" \
+        -f rawvideo -pix_fmt yuv420p10le -s 1280x720 -i "$OUT/SW_${name}.yuv" \
+        -filter_complex "[0:v]format=yuv420p10le[a];[a][1:v]ssim" \
+        -f null - 2>&1 | grep -oE "SSIM Y:[0-9.]+ " | head -1 | awk '{print $2}')
+    echo "  $name: SSIM_Y=$SSIM"
+}
+
+run_ssim hevc_main10 bbb_main10.mp4
+run_ssim h264_hi10p  bbb_hi10p.mp4
+
+# Step 5 — 5-codec smoke regression check (criterion 5)
+echo ""
+echo "==> Criterion 5: 5/5 PASS still holds for the iter38 baseline codecs"
+for codec in h264:bbb_1080p30_h264.mp4 hevc:bbb_720p10s_hevc.mp4 \
+             vp9:bbb_720p10s_vp9.webm vp8:bbb_720p10s_vp8.webm \
+             mpeg2:bbb_720p10s_mpeg2.ts; do
+    name="${codec%%:*}"; fixture="${codec#*:}"
+    [ -f "$HOME/fourier-test/$fixture" ] || { echo "  skip $name: fixture missing"; continue; }
+
+    env LIBVA_DRIVER_NAME=v4l2_request \
+        LIBVA_DRIVERS_PATH="$HOME/src/libva-v4l2-request-fourier/build/src" \
+        ffmpeg -hide_banner -loglevel error -y \
+        -hwaccel vaapi -hwaccel_output_format vaapi \
+        -i "$HOME/fourier-test/$fixture" \
+        -vf "hwdownload,format=nv12" -frames:v 10 \
+        -f rawvideo -pix_fmt nv12 "$OUT/L_${name}.nv12"
+    ffmpeg -hide_banner -loglevel error -y \
+        -hwaccel v4l2request -hwaccel_output_format drm_prime \
+        -i "$HOME/fourier-test/$fixture" -vf "hwdownload,format=nv12" \
+        -frames:v 10 -f rawvideo -pix_fmt nv12 "$OUT/K_${name}.nv12"
+    L=$(sha256sum "$OUT/L_${name}.nv12" | cut -c1-16)
+    K=$(sha256sum "$OUT/K_${name}.nv12" | cut -c1-16)
+    if [ "$L" = "$K" ]; then
+        echo "  $name: PASS"
+    else
+        echo "  $name: FAIL (libva=$L kdirect=$K)"
+        FAIL_COUNT=$((FAIL_COUNT + 1))
+    fi
+done
+
+echo ""
+if [ $FAIL_COUNT -eq 0 ]; then
+    echo "iter39 close: ALL PASS — Hi10P + Main10 wired + iter38 5/5 baseline holds"
+    exit 0
+else
+    echo "iter39 FAIL: $FAIL_COUNT criteria failed; see $OUT for artefacts"
+    exit 1
+fi