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+## Iteration 36 — Phase 8 (close): Remove env-gated DIAG probes
+
+Closes 2026-05-14, seventh campaign-day milestone after iter35 (MPEG-2 verification). User requested "clean up the env-gated diagnostics".
+
+### Removed (env-gated, no behavior change with env unset)
+
+- **iter29** `LIBVA_HEVC_DUMP_SLICE_TAIL` in `src/h265.c` — refuted 40-byte slice_data inflation theory before α-29 fix
+- **iter30** `LIBVA_TS_SCALE` in `src/picture.c` — refuted timestamp magnitude theory before α-29 fix
+- **iter33** `LIBVA_VP8_DUMP_FRAME` in `src/vp8.c` — led to discovering α-30 fix (header strip)
+- **iter35** `LIBVA_MPEG2_DUMP_FRAME` in `src/mpeg2.c` — confirmed libva MPEG-2 ctrls are semantically correct
+
+Total: **-131 lines / +7 lines** (one α-7 comment refresh to remove the iter30 reference).
+
+### Retained (framework-level, preexisting before this campaign)
+
+- `LIBVA_V4L2_DUMP_OUTPUT` (picture.c α-16) — bitstream OUTPUT dump; useful for future debugging, was instrumental in α-30 discovery
+- `LIBVA_V4L2_DUMP_CAPTURE` (surface.c) — sibling CAPTURE dump
+- `LIBVA_V4L2_ZERO_CAPTURE` (picture.c) — debugging knob to zero CAPTURE buffers
+- `LIBVA_V4L2_REQUEST_VIDEO_PATH` / `MEDIA_PATH` / `NO_AUTODETECT` (request.c) — required env config for device override
+
+### Regression test post-cleanup (kernel 7.0-14)
+
+| Codec | libva sha-16 | kdirect sha-16 | Status |
+|---|---|---|---|
+| H.264 | dd4f5f2d552c07bc | same | PASS |
+| HEVC  | 108f925bb6cbb6c9 | same | PASS |
+| VP9   | cf35908ae0f9ab60 | same | PASS |
+| VP8   | d3231e5b6c0ee10b | same | PASS |
+| MPEG-2| 95c5905890c937d4 | same | PASS |
+
+5/5 PASS. Identical hashes to pre-cleanup. No regressions.
+
+### Substrate state
+
+- Backend fork tip `7db15a5` (load-bearing fixes α-25 + α-29 + α-30 retained; env-gated DIAG probes removed)
+- Kernel `linux-fresnel-fourier 7.0-14` clean (unchanged)
+
+### Open items remaining (post-iter36)
+
+1. α-26 cosmetic revert — `decode_params->short_term_ref_pic_set_size = picture->st_rps_bits` is mis-routed (rkvdec doesn't use that field). Could revert to 0. Cosmetic; no behavior change.
+2. Libva multi-device probe — architectural change in libva backend (~200-400 LOC). Single-session H.264/HEVC/VP9 (rkvdec) + VP8/MPEG-2 (hantro) without `LIBVA_V4L2_REQUEST_VIDEO_PATH` override per codec. Design judgment from user welcome.
+
+Campaign in clean ship state. No urgent work.