initial seed: retrofit campaign lineage from local working trees

panvk-bifrost campaigns (r1..r4 Vulkan compositor + r5.video1 Vulkan
video decode) shipped before this repo existed; the deliverable
patches live in marfrit-packages, but the reasoning chain, phase docs,
and source-state evidence lived only in local working trees on the
development host.

This retrofit imports:
- mesa-panvk-bifrost/   — r1..r4 era phase docs (iter1..iter18)
                          (libmali stub blobs at iter18/blob/ excluded
                          — 109MB of RE artifacts replaced with a README
                          pointer)
- mesa-panvk-bifrost-video/ — sibling campaign phase docs + probe
- evidence/             — frozen .tgz source snapshots at each milestone
                          (basis for the 0005 patch diff generation)

Future iterations should branch off here from day one, so each iter is
a commit rather than a snapshot. See [[feedback-session-local-process-pins]]
for the process drift this retrofit closes.

Total: 1.9 MB across 124 files.

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

mesa-panvk-bifrost/phase0_findings_iter6.md

@@ -0,0 +1,63 @@
+# Phase 0 — substrate for iter6
+
+Opened **2026-05-19** after [iter5 close GREEN](phase8_iteration5_close.md).
+
+## Locked research question — iter6
+
+> **Render a depth-tested scene into a 128×128 RGBA8 color attachment + 128×128 D32_SFLOAT depth attachment via dynamic rendering:**
+>
+> - **Triangle A (red):** large, NDC (-0.8,-0.8), (0.8,-0.8), (0.0,0.8), all with z=0.7
+> - **Triangle B (green):** small, NDC (-0.4,-0.4), (0.4,-0.4), (0.0,0.4), all with z=0.3 — fully geometrically inside Triangle A
+> - Draw A first, then B. Depth test enabled (`VK_COMPARE_OP_LESS`).
+> - Triangle B's lower z should make it appear in front of A wherever they overlap.
+>
+> **Verify specific pixels:**
+> 1. `(0, 0)` — clear (outside both, top-left corner)
+> 2. `(127, 127)` — clear (outside both, bottom-right corner)
+> 3. `(64, 64)` — inside both, GREEN (B in front)
+> 4. `(64, 30)` — inside A only (above B's reach in pixel-y), RED
+> 5. `(64, 100)` — inside A only (below B's reach), RED
+
+## Why this shape
+
+iter5 closed all single-draw, no-depth, descriptor-binding paths. iter6 adds:
+
+- **Depth/stencil attachment** (D32_SFLOAT) — new image format, new aspect, new usage flag (DEPTH_STENCIL_ATTACHMENT)
+- **Depth test + depth write** in pipeline state (`VkPipelineDepthStencilStateCreateInfo`)
+- **Multi-draw within one render pass** — two `vkCmdDraw` calls between begin/end
+- **z-coordinate handling** in the vertex shader (gl_Position.z affects depth)
+- **128×128 image** instead of 64×64 (more tiles — 8×8 grid of 16×16 = 64 tiles)
+- **Depth attachment format** in `VkPipelineRenderingCreateInfoKHR.depthAttachmentFormat`
+- **Depth attachment** in `VkRenderingInfoKHR.pDepthAttachment`
+
+## Hypothesis space
+
+1. **D32_SFLOAT depth format on Bifrost.** Bifrost packs depth into tiles; the layout differs from color. First time we use a non-color attachment.
+2. **Depth-stencil image creation + layout (`DEPTH_STENCIL_ATTACHMENT_OPTIMAL`).** New layout never used.
+3. **Depth test plumbing.** PanVk-Bifrost's path from `VkPipelineDepthStencilStateCreateInfo` → tile descriptor depth-state fields.
+4. **Depth write back to depth attachment.** Mali stores depth in tile memory then flushes; per-tile flush + cache invalidation.
+5. **Multi-draw within one render pass.** Bifrost's binner may have bugs handling N>1 jobs per render pass — particularly around per-draw state changes.
+6. **z-coordinate from vertex shader.** Vertex output position.z passes through to rasterizer.
+7. **Tile binning at 128×128** (64 tiles vs. iter3's 16). More potential for binner state bugs.
+
+## In-scope (LOCKED 2026-05-19 for iter6)
+
+- 128×128 RGBA8 color + 128×128 D32_SFLOAT depth attachment.
+- 6 vertices (2 triangles) in one vertex buffer, vec3 pos + vec3 color.
+- Depth test enabled, depth write enabled, compare LESS.
+- Two `vkCmdDraw(3, 1, *, 0)` calls within one render pass.
+- 5-point pixel-level verification.
+
+## Out-of-scope (LOCKED 2026-05-19 for iter6)
+
+- Stencil (D32_SFLOAT has no stencil aspect anyway).
+- D24_UNORM_S8_UINT or other depth formats (iter would explore if iter6 fails).
+- Depth clear via load-op only (no separate clear-image).
+- Front-face culling, polygon-mode lines.
+- Indexed draws.
+- More than 2 triangles.
+- WSI / surface — still off-screen attachment + buffer readback.
+
+## Reference
+
+- Prior closes: [iter1](phase8_iteration1_close.md) — [iter5](phase8_iteration5_close.md).