docs: progress log — batch A+B landed, build gate reached

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

OPSTACK-PROGRESS.md

@@ -34,3 +34,88 @@ C4 `GetPlayerPosition` zero-vector sentinel · C5 unbounded-join-on-shutdown ·
 Then STOP for a build. See `OPSTACK-PROMPT.md` → `WHAT TO DO`.
 
 ---
+
+## 2026-07-27 — Q4 done: the design docs are in git
+
+**What:** `.gitignore` replaced the single `!CODEMAP.md` exception with `!*.md`, and committed
+`ARCHITECTURE.md`, `AUDIT-2026-07.md`, `CLAUDE.md`, `OPSTACK-PLAN.md`, `OPSTACK-PROGRESS.md`,
+`OPSTACK-PROMPT.md`, `REVIEW_FINDINGS.md`, `fable-idea.md` (commit `3128852`). `CODEMAP.md.bak` stays
+ignored (`.bak` doesn't match `*.md`).
+
+**Why first, out of queue order:** every `*.md` was ignored, so a `git commit` of this progress file
+would have silently recorded nothing. The whole unattended crash-safety discipline depends on this
+file being committable, so it had to lead.
+
+**Believed true / verified:** verified — `git ls-files "*.md"` now lists all nine.
+
+**UNVERIFIED:** nothing (no C++ touched).
+
+**Next single action:** Phase 0.5 tests + the Phase 1 skeleton header.
+
+---
+
+## 2026-07-27 — starting Phase 0.5 (tests) + Phase 1 skeleton header
+
+**Plan for this batch, written before doing it** (so an abrupt end leaves a marker):
+
+1. `Source/VoxelForge/Private/Tests/VoxelForgeDeterminismTest.cpp` — density purity, shuffled order,
+   multi-threaded (`ParallelFor`), bit-equality.
+2. `Source/VoxelForge/Private/Tests/VoxelForgeClassifyTileTest.cpp` — `ClassifyTile` verdict vs a
+   brute-force sweep of the exact mesher lattice.
+3. `Source/VoxelForge/Private/Tests/VoxelForgeDiffLayerTest.cpp` — N readers + 1 writer, monotonic
+   version, no crash.
+4. `Public/VoxelDensityOp.h` — the Phase 1 contract. HEADER ONLY, nothing wired into `GetDensityAt`.
+
+**Known design constraint found while reading:** `ClassifyTile` and `GetDensityAt`'s per-chunk caches
+need a live `UVoxelStrateManager`, whose only entry point is
+`Initialize(UVoxelSettings*, int32)` reading `TSoftObjectPtr` pools. Tests therefore build transient
+`UVoxelStrateDefinition` objects and point soft pointers at them. **If that resolve turns out not to
+work headless, test 2 self-skips rather than failing** — noted here because a skip that looks like a
+pass is exactly the kind of thing that hides a bug.
+
+**UNVERIFIED:** everything below this line until Jahni builds. No test has ever been compiled in this
+plugin — `Private/Tests/` is a new directory and the module has never pulled in `AutomationTest.h`.
+
+**Next single action:** write the three test files.
+
+---
+
+## 2026-07-27 — batch A+B landed, BUILD GATE reached
+
+**Commits, oldest first:**
+
+| Commit | What | Risk |
+|---|---|---|
+| `3128852` | `.gitignore !*.md` + the eight design docs into git (Q4) | none |
+| `6eec796` | the three Phase 0.5 tests + `VoxelForgeTestFixture.h` | new files only |
+| `d41d34e` | `Public/VoxelDensityOp.h` + `EVoxelTileClass` moved to `VoxelTypes.h` | header-only |
+| `73f6b26` | **AUDIT C2 fix** — five caches now key on `GetLayoutVersion()` | ⚠️ the only commit that touches a hot path |
+| `b4d13e0` | regression test for C2 | new file only |
+
+**Believed true:** `73f6b26` is behaviour-neutral at a static layout — the layout version only
+moves on `Initialize`, so a running world sees the same keys it saw before, plus one `uint32`
+compare per chunk-change. It changes behaviour only after a `RebuildStrates` / editor live edit,
+which is the bug.
+
+**Design decision worth not re-litigating:** `ClassifyBox` in `VoxelDensityOp.h` is deliberately
+NOT source-only. `ApplyBoundarySeal` does `Max(D, SealFactor·BaseDensity)` inside its band — it
+*forces* solid regardless of input, and pure direction (`FillOnly`) cannot express that. Over a box
+sitting entirely in the top seal band the source says AllAir, `FillOnly` kills AllAir, both
+hypotheses die → Mixed, whereas `ClassifyTile` returns AllSolid there today. Not a hole, but a
+silent loss of exactly the trivial tiles T1.d exists to skip. So forcing ops reset the fold, and
+ops after them still apply. The full mapping from the fold to today's `ClassifyTile` is written out
+in the header.
+
+**Deliberately NOT done, and why:** AUDIT **C1** (unbounded `SeedF`) is a one-line fix at six
+sites, and `OPSTACK-PLAN §8` lists it first. I left it. It is dormant at small seeds, and applying
+it changes `SeedF` from `Seed` to `hash(Seed)&0x3FFF` — i.e. it re-rolls the whole world's noise
+even at today's seed, forcing a re-tune. Doing that in the same build Jahni is using to judge four
+other unverified changes costs him attribution for no present-day benefit. It should land on its
+own, deliberately, when he has an hour to re-tune. **It is still a real bug — do not lose it.**
+
+**UNVERIFIED — everything above.** None of it has been compiled. In particular the test fixture's
+`TSoftObjectPtr` → transient-object resolve has never run.
+
+**Next single action:** build-free queue. Q1 (`OPSTACK-DECOMPOSITION.md`), then Q2, then Q3.
+
+---