feat(opstack C3): TunnelNetwork + Underwater in the ported list -- 8 of 8

UsesOperatorStackForChunk now returns true for both, so the archetype switch has a complete
operator-stack twin: per-strate opt-in, every archetype equivalence-tested bit for bit against its
original function.

This changes nothing by itself. The flag still requires bUseOperatorStack ticked on a strate asset,
which is Jahni's call and was deliberately NOT done. What HAS changed is that the flag is no longer
a no-op anywhere: ticking it on any strate now really switches that strate onto the stack.

Not done, and it is the next real prize: ClassifyTile still uses hand-written guards and does not
consume ClassifyBox. That is where measured tile-skipping becomes frames.

DOCS
- CODEMAP 3.2d: ported list 6 of 8 -> 8 of 8; the BuildTunnelNetworkStack row rewritten (19 ops, one
  builder for two archetypes); six new rows for the detail modifiers, each carrying the thing a
  reader would otherwise have to rediscover -- roughness reads STRATE params, terrace re-queries the
  SDF, the cliff's comment disagrees with its code, columns have no strate parameter at all, and
  LocalParams() is the override whose EffectOverBox is too optimistic on a strate with an op pool.
  Also corrected the stale "never compare the two paths" line: C10 is closed and all eight
  equivalence tests compare bit for bit.
- CODEMAP 3.3 UsesOperatorStackForChunk row: same list, plus the warning that the flag is now a real
  switch rather than a harmless tick.
- OPSTACK-PLAN: status header and the Phase 2 order both updated; the three-stage TunnelNetwork
  breakdown and the calls-not-transcribes rule recorded there rather than only in the code.
- OPSTACK-PROGRESS: the closing entry for this unattended run -- every commit in order, the five
  original-code findings ported as-is, the two decisions that are not reversible by taste, the
  ClassifyBox optimism C1 introduced and that must be fixed before ClassifyTile consumes it, what
  breaks first per group, and the likely compile-error spots.

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

CODEMAP.md

@@ -121,11 +121,15 @@ stack share ONE copy. `VoxelGenerator.cpp` keeps same-named `static FORCEINLINE`
 ⚠️ **Feeds the game, behind a per-strate opt-in** (Phase 1 step 3). `GetDensityAt` builds the stack
 in its per-chunk refetch block and evaluates it *instead of* the `switch` only when
 `UVoxelStrateManager::UsesOperatorStackForChunk` says so — strate ticked `bUseOperatorStack` **and**
-archetype in the ported list (**Maze, FlatPlain, CrystalChamber, SurfaceWorld, VerticalShafts,
-FloatingIslands** — 6 of 8). Everything else still takes the `switch`, unchanged.
-**`ClassifyTile` is NOT wired** — still hand-written guards, not `ClassifyBox`. That is Phase 2.
-⛔ Never run both paths in one world, and never compare them for equality: the ~1 ULP residue is
-inherent (AUDIT §C10). The acceptance bar is visual (OPSTACK-PLAN §2.6).
+archetype in the ported list, which is now **all 8 of 8**: Maze, FlatPlain, CrystalChamber,
+SurfaceWorld, VerticalShafts, FloatingIslands, TunnelNetwork, Underwater. A strate that has not
+ticked the box still takes the `switch`, unchanged — the flag is the only thing that switches paths.
+**`ClassifyTile` is NOT wired** — still hand-written guards, not `ClassifyBox`. That is the next
+piece, and it is where the measured tile-skipping turns into frames.
+⛔ Never run both paths in one world. **Comparing them IS legitimate now** — the ~1 ULP residue of
+AUDIT §C10 is gone since `FPSemantics = Precise`, and all eight equivalence tests compare bit for
+bit. They are port-correctness oracles, not fidelity checks: the acceptance bar is §2.6.1 (same seed
+⇒ same world on every peer), which does not require resembling the pre-refactor world.
 
 | Symbol | Role | Notes |
 |--------|------|-------|
@@ -145,7 +149,14 @@ inherent (AUDIT §C10). The acceptance bar is visual (OPSTACK-PLAN §2.6).
 | `VoxelDensityOps::BuildVerticalShaftStack` | — | 8 ops, and **three are Maze's reused unchanged** (`ConstantRock`, `SdfRoughness`, `SdfCarve`) with different tuning (freq 0.1 vs 0.12, window `rough+4` vs `R+rough+2`). The measured proof of `OPSTACK-PLAN §2.5`'s reuse claim. |
 | `FRoomGraphSource` (internal) | 1 | TunnelNetwork's SDF spine. **CALLS `BuildChunkCache`/`EvaluateSDFCached` — does not transcribe them**: that is where §8.4's two-region discipline lives and a copy would fork it. Owns the cave warp (scope = this op alone; pits/chimneys read *unwarped* coords, which is why no FRAME op was needed). Its cache key adds a **params CRC + LayoutVersion** that the original lacks — see the suspected staleness note in AUDIT §C2. `EffectOverBox` → `Both` for now (a real answer means building the cache for the queried box; only pays once `ClassifyTile` consumes `ClassifyBox`). |
 | `FWormFieldSource` (internal) | 1 | Fielded 3D-noise threshold carve, masked by distance to the room network (reads `InOut.Sdf` *after* pits/chimneys). `EffectOverBox` → **`CarveOnly` everywhere** — no spatial bound, so it kills `AllSolid` on every tile of every strate with worms on. `MaxCarveAmplitude()` holds the bound from DECOMPOSITION §0.2 that would recover it, waiting for a fold that carries numbers. |
-| `VoxelDensityOps::BuildTunnelNetworkStack` | — | **STAGE A of three — incomplete on purpose.** 6 ops: rock → room graph → carve → worms → structural ×3. The 13 detail modifiers (stage B) and the per-room op override (stage C) are missing, which is why TunnelNetwork is still **off** in `UsesOperatorStackForChunk`. Testable now because every detail modifier is amplitude-gated and defaults to 0. |
+| `VoxelDensityOps::BuildTunnelNetworkStack` | — | **COMPLETE, 19 ops** — the biggest port in the plugin (~1080 lines), done in three stages: SDF spine (A) → the twelve detail modifiers of 4b–4h (B) → the per-room op override (C). Serves **TunnelNetwork and Underwater** from one builder. Operator order is the original's, line for line, and it is load-bearing (`FFloorBiasMod` exists to undo what `FCaveRoughnessMod` did to floors). |
+| `FCaveRoughnessMod` (internal) | 3 | STEP 4b, **density space** — a different op from `MakeSdfRoughnessMod`: two octave sets, optional domain warp, four noise types, an anti-fill clamp inside definite air, quadratic fade. ⚠️ **Reads STRATE params, not the per-room copy** — the original's shadow is declared *after* step 4b. Eleven of twelve modifiers read the room copy; this one does not. |
+| `FCaveTerraceMod` (internal) | 3 | STEP 4c. The only modifier that **re-queries the SDF** (Z±1, through `FRoomGraphSource::ProbeSdfUnwarped`) for its horizontality gate — which is why the room source's cache is exposed at all. ⚠️ Those probes use unwarped X/Y and raw Z although the field was evaluated warped: transcribed as-is, see OPSTACK-PROGRESS. |
+| `FLayerLineMod` / `FRibbingMod` (internal) | 3 | The same sine along Z: cubed and subtracted (grooves) vs quarter-phase-shifted, squared and added (ribs). `CarveOnly` / `FillOnly` — two of the few detail modifiers that keep a usable direction for the fold. |
+| `FCaveOverhangMod` / `FCaveCliffMod` / `FScallopMod` (internal) | 3 | STEP 4c. ⚠️ The cliff's own comment promises a sampled vertical gradient; the **code** uses a Z-stretched Perlin as a proxy and samples nothing. Ported as written — fixing it would change the world. |
+| `FCaveArchMod` / `FDomeMod` / `FPinchMod` / `FFloorBiasMod` (internal) | 3 | Room-relative: they read `FRoomGraphSource::GetNearestRoomIdx()` and the cached room. Their gate is `SDF < SDFBlendRadius`, **not** the shared `·3` one — they live in the cave's void, not its wall. |
+| `FRoomColumnMod` (internal) | 3 | STEP 4d, and **not** `MakeGridColumnMod`: it walks `SDFCache.Columns`, pre-baked per room. ⚠️ It has **no strate parameter at all** — neither the bake nor the loop reads `FStrateGenerationParams::ColumnDensity`. Columns exist only through a `Column` terrain-op asset in the strate's pool, and the only way to prove they fired is to look at `SDFCache.Columns.Num()`. |
+| `FRoomGraphSource::LocalParams()` | — | **The per-room op override** (DECOMPOSITION §2's "no clean home"). Strate params + the nearest room's `UVoxelTerrainOpDefinition::ApplyTo`, memoised once per voxel and read by eleven modifiers. One op owns the shared state, the rest read it — the same pattern as `FOverhangShelfMod` ← `FSurfaceColumnSource`. ⚠️ `EffectOverBox` still answers from STRATE params, so a box verdict can be **too optimistic** on a strate with a terrain-op pool; harmless until `ClassifyTile` consumes `ClassifyBox`, and it must be fixed before that. |
 | `FIslandBlobSource` (internal) | 1 | Hash-placed tapered flat-top blobs, `SmoothMin`'d, in a **domain-warped XY frame** (the warp stays inside the op — see the deviation note vs DECOMPOSITION §7). SDF channel only. `EffectOverBox` → `FillOnly` when a blob reaches the box, `Identity` otherwise; its pad must cover warp·**√2** (two independent noise axes), roughness, fill blend and the `SmoothMin` dip. **No lower Z bound exists** — a hairline thread of matter hangs below each island down its axis, so only the TOP may reject. |
 | `VoxelDensityOps::BuildFloatingIslandStack` | — | 7 ops, and **the stack runs backwards**: void source + fill instead of rock source + carve, using the *same* classes with the opposite sign. Only the blob source is new. Reuse by **inversion** — a stronger result than reuse by identity, since it says the abstract axis (the density sign) is the right one. |
 | `VoxelDensityOps::BuildMazeStack` | — | The 7-op Maze stack. If this ever becomes one op, the refactor failed its own test (§2.5). Callers must skip it on a **degenerate strate** (top−bottom ≤ 0): `GetMazeDensity` early-outs to air there and the stack has no such early-out by design — `GetDensityAt` falls back to the `switch`. |
@@ -327,7 +338,7 @@ Maps depth→strate at runtime; owns passages.
 | `GetLayoutVersion` | h:161 (inline) | Layout/passage generation counter (= `PassagesVersion`, bumped by every `Initialize`). Hot-path callers key `thread_local` memos on it (strate-index memo in `GetDensityWithParams`, passage shortlist) so editor rebuilds never serve stale data. |
 | `GetStrateForChunk` | 466 | Chunk → definition. |
 | `GetGeneratorTypeForChunk` | 476 | Chunk → generator type. |
-| `UsesOperatorStackForChunk` | 559 | Chunk → should `GetDensityAt` take the operator stack? `bUseOperatorStack` on the definition **AND** archetype in the ported list (Maze, FlatPlain, CrystalChamber, SurfaceWorld, VerticalShafts, FloatingIslands — 6 of 8; missing: TunnelNetwork, Underwater). **That list is written down here and nowhere else** — an unported archetype ignores the flag, so ticking the box anywhere is harmless. Add a row here when you port one. |
+| `UsesOperatorStackForChunk` | 559 | Chunk → should `GetDensityAt` take the operator stack? `bUseOperatorStack` on the definition **AND** archetype in the ported list — **now all 8 of 8** (Maze, FlatPlain, CrystalChamber, SurfaceWorld, VerticalShafts, FloatingIslands, TunnelNetwork, Underwater). **That list is written down here and nowhere else.** With every archetype ported the flag is now the *only* thing that decides the path, so ticking the box is no longer a no-op anywhere — it is a real switch onto the operator stack for that strate. |
 | `GetSlabParamsForChunk` | 490 | Slab params with runtime Z bounds (no blend — slabs use Hard). |
 | `GetBiomeContextForChunk` | — | Flatten the strate's `Biomes[]` + `BiomeMapParams` into a POD `FBiomeContext` for the biome field. Empty ⇒ biomes disabled. §8.14. |
 | `GetGenerationParams` | 515 | **Blended** TunnelNetwork params (handles Gradient/Hard/Interleaved transitions). |