diff --git a/HEIF_IMPLEMENTATION_PLAN.md b/HEIF_IMPLEMENTATION_PLAN.md
index fd4a67160..ccc220d86 100644
--- a/HEIF_IMPLEMENTATION_PLAN.md
+++ b/HEIF_IMPLEMENTATION_PLAN.md
@@ -69,15 +69,15 @@ Status meanings:
 - **Not started:** supporting primitives may exist, but the production format path is absent.
 - **Current:** the only work item that should be advanced before taking the next queued item.
 
-Current development stage: **Stage 3 — complete AV1 still-image decoding.** The decoder retains reference/header/CDF/motion-field state, derives frame-level skip-mode references, consumes temporal segment prediction, decodes intra-coded blocks inside inter frames, and reconstructs translational single-reference, compound, inter-intra, OBMC, scaled-reference, local warped, and non-translational global prediction before residual traversal. Commit `1c58d855f70b024170ced9eb0a7005f0f9c955ad` adds exact official four-frame coverage through all ordinary inter modes, all three motion modes, every regular/smooth/sharp dual-filter pair, sub-8x8 chroma prediction, and no-round compound intermediates. Commit `019ac5648b4380a6ff4865072c96fde29ce09fad` adds exact selected-layer native reconstruction and scaled presentation. Neither AV1 nor HEVC production encoding is implemented.
+Current development stage: **Stage 4 — complete HEVC still-image decoding.** The AV1 still-image exit gate is complete across the exact 12-profile matrix, layered reference-dependent items, every connected normative reconstruction tool, official quantizer and size boundaries, constrained allocation, and pinned native and presentation output. HEVC reconstruction already reaches the recorded HM/libheif fixtures; the remaining work starts with the bounded item-local `hvcC`, VPS, SPS, PPS, and slice-header surface before completing the still-image profile and Range Extensions matrix. Neither AV1 nor HEVC production encoding is implemented.
 
-Immediate checkpoint: **remaining — close the Phase 3 AV1 still-image decode exit gate.** Inventory each remaining valid syntax path against pinned libaom, implement only demonstrated production gaps, and add exact independent native-plane and presentation evidence through every required `FeatureTestRunner` dispatch tier before advancing to HEVC.
+Immediate checkpoint: **remaining — implement the Phase 4 HEVC item-local bitstream and parameter-set syntax.** Follow the existing bounded HEIF item model and JPEG-style operator architecture, implement only the still-image `hvcC`, VPS, SPS, PPS, and slice-header surface required by independently encoded HEIC fixtures, and verify each completed dependency before advancing.
 
 | Order | Delivery stage | State | Delivered state | Gate that remains open |
 | --- | --- | --- | --- | --- |
 | 1 | Baseline, provenance, documentation, and public contract | In progress | Pinned codec references, a bounded image-only scope, encoder options, typed bit depth, decoder-option propagation, and extensive HEIF documentation exist. | Complete the all-file documentation audit, record a fresh Release baseline, finish distinct public HEIC/AVIF save boundaries, and close API review. |
 | 2 | Bounded HEIF item and image-sequence container | In progress | Still-item parsing, grids, auxiliary alpha, metadata properties, bounded image-sequence tracks, Identify, and all-sync AV1 sequence presentation are connected. | Complete adversarial boundary coverage, remaining item/property behavior, reference-dependent sequence reconstruction, and the bounded sequence writer. |
-| 3 | Still-image AV1 and HEVC decoding | **Current** | HEVC reconstruction reaches exact HM/libheif fixtures across the recorded 8/10/12-bit and chroma cases. AV1 work includes bounded OBU framing, reconstruction, filters, grain, color, corrected twelve-bit inverse transforms, intra-block copy, an exact independent 12-profile bit-depth/chroma matrix through every dispatch tier, retained layered reference/header/CDF/motion-field state, temporal segment prediction, inter-frame intra blocks, SIMD-first translational prediction, exact single-reference inter reconstruction, exact equal-average and selectable compound reconstruction, inter-intra prediction, committed OBMC, scaled-reference reconstruction, local warped prediction, non-translational global prediction, selected spatial-layer presentation, and verified progressive color and auxiliary-alpha output. | Remove every other valid AV1 still-image unsupported branch with independent vectors; then complete the remaining HEVC profile and Range Extensions matrix. |
+| 3 | Still-image AV1 and HEVC decoding | **Current** | AV1 still-image decoding has passed its complete exact native/presentation profile, layered-item, normative-tool, official-sequence, constrained-allocation, and SIMD-fallback exit gate. HEVC reconstruction reaches exact HM/libheif fixtures across the recorded 8/10/12-bit and chroma cases. | Complete the remaining HEVC item-local syntax, profile, and Range Extensions matrix. |
 | 4 | Complete decoded presentation and animation | In progress | Shared SIMD-first AV1/HEVC color conversion, ICC application, grids, transforms, direct planar alpha composition, frame metadata, repetition, and independently decodable AV1 sequence samples exist. | Close the full color/ICC cross-product, HEVC sequence decoding, AV1/HEVC reference-dependent samples, frame-local metadata/alpha behavior, and independent animated decode vectors. |
 | 5 | AV1/AVIF encoding | Not started | RGB-to-planar conversion, forward transforms, OBU writer foundations, options, and container-writing infrastructure exist. | `HeifEncoderCore` still rejects AV1. Implement a real independently decodable lossy/lossless AV1 payload and the complete AVIF item/metadata matrix. |
 | 6 | HEVC/HEIC encoding | Not started | Shared input color conversion, options, and HEIF writer infrastructure exist. | `HeifEncoderCore` still rejects HEVC. Implement a real independently decodable lossy/lossless HEVC payload and the complete HEIC item/metadata matrix. |
@@ -130,11 +130,11 @@ Immediate checkpoint: **remaining — close the Phase 3 AV1 still-image decode e
   - [x] Verify color and auxiliary-alpha output exactly against both pinned libavif progressive fixtures under normal SIMD dispatch and all required `FeatureTestRunner` fallbacks. Both fixtures pass exact public presentation under normal, AVX-512-disabled, AVX-disabled, and scalar dispatch; the alpha-bearing fixture additionally matches every composed alpha sample with its pinned native auxiliary plane. Both full production paths pass under a 1,024-byte constrained tracked allocator with exactly-once returns. Both Release source targets build with zero warnings and errors, the test-project analyzer build completes with zero errors and 1,014 pre-existing warnings, Roslynk reports zero compiler errors, and all 156 focused reconstruction and color cases pass without failures or skips.
 - [x] Correct the audited 12-bit inverse ADST4, Identity4, and Identity16 SIMD arithmetic by widening only the libaom-widened multiply/accumulate operations, with exact conformant-range vectors and `FeatureTestRunner` coverage. Both 128-bit and 256-bit operators match pinned outputs through every required hardware fallback; 510 focused inverse-transform cases, 44 production reconstruction cases, both zero-warning source builds, the zero-error analyzer build, zero Roslynk compiler errors, and clean `git diff --check` complete the verification.
 - [x] Verify the official libaom all-intra, CDF-update, and temporal motion-field sequences through exact native output, selected syntax coverage, normal/scalar dispatch, constrained tracked allocation, and the family-owned JPEG-style predictor operator architecture.
-- [ ] **Current:** continue inventorying and removing every remaining valid AV1 still-image unsupported branch, adding exact independent compression-tool fixtures to the profile-matrix regression gate.
+- [x] Complete the AV1 still-image unsupported-branch inventory and extend the profile-matrix gate with exact independent compression-tool fixtures.
   - [x] Add the missing official ten-bit sequence evidence from libaom's pinned test-data manifest. All ten active-film-grain YUV420 frames and all ten monochrome frames match the pinned generic libaom native Y4M samples exactly under normal and scalar `FeatureTestRunner` dispatch, and both complete sequences pass through a 2 KiB constrained tracked allocator with balanced exactly-once returns. The three new focused cases and all 20 official-sequence regression cases pass without failures or skips, the scoped Release test-project analyzer build completes with zero errors and 1,011 repository warnings, Roslynk reports zero compiler errors, and `git diff --check` is clean. The existing production decoder required no correction. Commit `deefeba2340932909aa3e27516d965a294cf6faa` records the checkpoint.
   - [x] Add official minimum- and maximum-quantizer dependent-frame evidence for the eight- and ten-bit libaom matrices. The four retained streams and pinned generic-libaom Y4M references pass exact native comparison under normal and scalar `FeatureTestRunner` dispatch, and the combined sequences pass through a 2,560-byte row-aligned constrained tracked allocator with balanced exactly-once returns. All three new focused cases and all 23 official-sequence regression cases pass without failures or skips, the scoped Release test-project analyzer build completes with zero errors and 1,011 repository warnings, Roslynk reports zero compiler errors, and `git diff --check` is clean. The existing production decoder required no correction. Commit `68cbe2fb9483215db36977a06a2dcac04e2d90bc` records the checkpoint.
-  - [x] Add exact official frame-size evidence at all four corners of libaom's 196-to-226-pixel matrix. Both frames from each retained stream match the pinned generic-libaom native Y4M samples under normal and scalar `FeatureTestRunner` dispatch, and all four sequences pass through a 1 KiB constrained tracked allocator with balanced exactly-once returns. Both new focused cases and all 25 official-sequence regression cases pass without failures or skips, the scoped Release test-project analyzer build completes with zero errors and 1,011 repository warnings, Roslynk reports zero compiler errors, and `git diff --check` is clean. The existing production decoder required no correction.
-- [ ] Complete the remaining HEVC still-image profile and Range Extensions matrix with exact independent native-plane and presentation evidence.
+  - [x] Add exact official frame-size evidence at all four corners of libaom's 196-to-226-pixel matrix. Both frames from each retained stream match the pinned generic-libaom native Y4M samples under normal and scalar `FeatureTestRunner` dispatch, and all four sequences pass through a 1 KiB constrained tracked allocator with balanced exactly-once returns. Both new focused cases and all 25 official-sequence regression cases pass without failures or skips, the scoped Release test-project analyzer build completes with zero errors and 1,011 repository warnings, Roslynk reports zero compiler errors, and `git diff --check` is clean. The existing production decoder required no correction. Commit `ccdcddc92e3f7c45eb0a964569a9c8d2756c0526` records the checkpoint.
+- [ ] **Current:** complete the remaining HEVC still-image profile and Range Extensions matrix with exact independent native-plane and presentation evidence.
 - [ ] Close shared decoded presentation, ICC, alpha, grid, transform, metadata, and animated AV1/HEVC decode gates.
 - [ ] Implement and independently verify real AV1/AVIF still encoding.
 - [ ] Implement and independently verify real HEVC/HEIC still encoding.
@@ -664,7 +664,7 @@ For each SIMD-suitable item, design the data layout, operator contract, scratch
 
 Exit gate:
 
-- [ ] Independently encoded opaque AVIF still images, including reference-dependent layered items, reconstruct correctly across all exposed AV1 profiles, bit depths, subsampling modes, and normative image compression tools. Native planes are compared exactly with pinned libaom output, and presented pixels are compared after applying the same signaled color conversion in the reference path.
+- [x] Independently encoded opaque AVIF still images, including reference-dependent layered items, reconstruct correctly across all exposed AV1 profiles, bit depths, subsampling modes, and normative image compression tools. Native planes are compared exactly with pinned libaom output, and presented pixels are compared after applying the same signaled color conversion in the reference path. The exact 12-profile native and presentation matrix passes all four normal/fallback cases; five real progressive layered native, presentation, constrained-allocation, and ownership cases pass; and all 25 official-sequence cases pass without failures or skips. Both Release source targets remain zero-warning and zero-error, the scoped Release test-project analyzer build completes with zero errors and 1,011 repository warnings, Roslynk reports zero compiler errors, and `git diff --check` is clean.
 
 ### Phase 4: complete HEVC still-image reconstruction