feat(composer): F1 -- the candidates are VISIBLE, and detail is invisible

PART B: the preview. Jahni, asked what "good" means for ranking a season:
"good is hard to describe, i believe it'll be easier once i'm able to see
the strates candidates." So the ranking policy was blocked on this, not on
more metrics. COMPOSER-NOTES §3.4 promised the preview comes nearly free
once the measurement exists; collected.

Per candidate, rendered from the grid the measurement ALREADY built (no
second sampling of the world): a vertical XZ section and a plan XY slice,
solid dark, air light, walkable cells highlighted, with a chunk scale bar
so a corridor is distinguishable from a cathedral. Plus a self-contained
index.html contact sheet of all 64 -- survivors first, outliers first
within them, recipes, metrics, and every rejected candidate labelled with
WHY (vacuous 3, fragmented 2, law failed 19).

  Saved/ComposerPreview/<runid>/index.html   64 candidates, 128 PNGs

Two honesty rules are on the page itself, not buried in a comment: every
number states the window that produced it (margin/step/Z span), and a
2D slice CANNOT show connectivity -- two regions that look joined in one
slice may not be.

Plan-Z is chosen by highest solid/air boundary-transition count, not
hardcoded mid-height; a slab strate would otherwise render as a blank
sheet. Codex flagged the ambiguity in my spec and picked correctly.

PART A: bootstrap jitter for zero-spread fields. ±25% of a field's own
magnitude when corpus spread is ~0, ±15% of measured spread otherwise,
clamps last. Marked in code as a BOOTSTRAP for a starved corpus that
promotion (Tier 5) should retire. 1,422 applications over 168 fields in
the parameter roll; 6,848 over 107 in the structure roll.

⚠️ AND IT DID NOT BROADEN THE DISTRIBUTIONS. Feature scale 0-376 either
way; walkable actually NARROWED (.389 -> .287). Codex's conclusion, and I
agree: the measurement is INSENSITIVE to these fields, not merely
corpus-starved.

The reason is now obvious and worth writing down: the grid samples every
4 voxels, and cave DETAIL -- terraces, scallops, ribbing -- lives at 1-3
voxels. It is below the sampling resolution. A step-4 grid structurally
cannot see feel; it sees size. So "vary the detail" and "score the detail"
need different instruments, and the preview images inherit the same limit.

Box proofs stayed sound under wider jitter: parameter roll 1,204 proved /
1,602,524 voxels / 0 violations; structure roll 659 proved / 877,129 /
0 violations. §6.2 did not reopen.

fable-idea.md F1 ticked (measurement + preview).

Build clean, 25 succeeded / 0 failed, verified by me.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VJiTcTSDNkKBtnNdiBtdaU

CODEMAP.md

@@ -319,6 +319,8 @@ the inclusive/exclusive voxel Z window used, the exact sampled dimensions/bounds
 component's deterministic lowest-cell representative point, cell count, and count of components
 holding at least 1% of the air. The flood fill also retains component cell counts in discovery order,
 so diagnostics can classify small non-largest components without a second source sample.
+Callers may optionally receive that exact polarity grid as `FVoxelStrateSampleGrid`; the editor-only
+composer preview consumes this hand-off rather than sampling the world again.
 `VF_AreConnected` recovers a deterministic BFS parent path from the same kind of grid and checks
 candidate routes at full voxel resolution before returning `Connected`. When a candidate is
 refuted, its specific coarse cell edge is added to a deterministic array blocklist and BFS is
@@ -334,6 +336,7 @@ No UObject state, cache, actor, world, or PIE is required.
 | Symbol | Role |
 |--------|------|
 | `FVoxelStrateMeasureSettings` / `FVoxelStrateMetrics` | Plain settings/result structs for bounded strate sampling and derived measurements; callers may override the interior margin (including zero to sample the seal) or fit the XY window to two points with a margin, and results identify the resolved window/dimensions/Z range and deterministic component representatives/sizes. |
+| `FVoxelStrateSampleGrid` | Optional one-pass `density > 0` air/solid capture exported by the measurement functions; bounded by `MaxCells`, consumed by editor/automation previews, never retained on ordinary metrics calls. |
 | `VF_MeasureStrate` | One-grid/one-flood-fill strate metrics; resolves either the legacy centered square or the two-point fitted AABB, and refuses invalid bounds or a grid over `MaxCells`. |
 | `VF_AreConnected` | Coarse 6-connected BFS plus deterministic blocked-edge retries, with a full-resolution air recheck for every candidate route and explicit endpoint-solid, out-of-window, `NotConnectedAtThisResolution`, `CoarseLiedBudgetExhausted` (unknown), and connected outcomes; diagnostics include endpoint component facts and the retry count from that same grid. |
 | `VF_DiagnoseConnectivity` | The same query plus each mouth's air-component size/share and exact geometric distance to the nearest cell of the other component; proximity is measured in coarse-cell coordinates and does not claim a route through solid. |
@@ -453,7 +456,8 @@ remain excluded. Live fields receive one matching `UVoxelTerrainOpDefinition` he
 in addition to authored strate values, so an all-default strate corpus still has useful activation
 spread. Rolls are pure in `(corpus contents, seed, index)`: weighted 2–3-parent same-archetype
 selection → `FStrateGenerationParams::Lerp` or reflected native-family blend → ±15% of measured
-field range jitter → editor-reflection clamps → ordered-pair repair. Bool
+field range jitter (or the season-zero ±25% own-magnitude bootstrap for near-zero ranges) →
+editor-reflection clamps → ordered-pair repair. Bool
 `bTunnelsFlowTowardOrigin` inherits from the dominant parent; integer/enum SNAP fields are not
 jittered. This API is not called by runtime generation. The settings audit found **one unique path**,
 `/Game/VoxelForge/DA_Strate3`, which explains the old one-vector corpus; the project assets were
@@ -468,6 +472,13 @@ it. `RequiredResources` / `ProvidedResources` close the room-state hole that cha
 could not express. `VoxelForgeComposerStructureRollTest` rolls 64 candidates, measures them through
 the offline sampler, and brute-forces every uniform box verdict from the novel stack itself.
 
+**`Public/VoxelStratePreview.h` + `Private/VoxelStratePreview.cpp`** — editor/automation-only PNG
+renderer and self-contained contact sheet. It consumes `FVoxelStrateSampleGrid` from the measurement
+pass, emits deterministic centre-Y XZ and data-selected XY slices via `IImageWrapper`, caps each
+image at 512 pixels (including its scale footer), and sorts the 64-card sheet by survivor status then
+descending corpus-centroid distance. The page repeats each candidate's exact measurement window,
+marks rejection reasons, explains the 2D-connectivity limitation, and has no runtime generation hook.
+
 ### 3.9 Player edits — `Public/VoxelDiffLayer.h` + `.cpp`
 `UVoxelDiffLayer : UObject` (h:77). Stores `FVoxelModification` (h:43: Center/Radius/Strength;
 **negative Strength = carve, positive = fill**) grouped by chunk in `TMap ChunkMods`.
@@ -531,9 +542,9 @@ The plugin's first tests (`OPSTACK-PLAN.md` Phase 0.5). Run them from the editor
 | `VoxelForgeOpStackIslandTest.cpp` | `VoxelForge.OpStack.FloatingIslandEquivalence` | The port that runs the stack **backwards** — void + fill vs rock + carve, same classes with the opposite sign. Counts interior-solid and open-void samples separately (on this archetype an aggregate "N solid" is dominated by the seal bands and says nothing about the islands). Counts `AllSolid` and `AllAir` verdicts **separately** too: `AllAir` is the one no cave archetype could ever prove, and it is the entire perf argument here. |
 | `VoxelForgeOpStackMazeTest.cpp` | `VoxelForge.OpStack.MazeEquivalence` | **Phase 1's load-bearing test.** The 7-op Maze stack vs `GetMazeDensity` over 20k points (aiming for bit-identity; a side-of-iso disagreement is the hard fail), plus purity across workers and brute force on every box verdict the stack emits. Reports how many tiles the stack can prove uniform — today's `ClassifyTile` proves **zero** for any cave archetype. |
 | `VoxelForgeStrateParamCoverageTest.cpp` | `VoxelForge.Determinism.StrateParamBlendCoverage` | **The X-macro guard** (added 2026-08-17). `FStrateGenerationParams::Lerp` blends the hand-written `VF_STRATE_PARAM_FIELDS` list, **not** the struct — so a field added to one and not the other compiles, tests green, and silently takes its **default** inside every Gradient/Interleaved transition band. This expands the X-macro a **third** way (after LERP and SNAP), into a name list, and diffs it against the struct's UObject reflection. Pure shape test: no fixture, no world, instant. `GExemptFieldNames` is **empty** — every reflected field is covered today, and any exemption must be written down as a decision. Stakes rise with the world composer, which intends to invent parameter sets through this same `Lerp` (`COMPOSER-NOTES.md`). |
-| `VoxelForgeComposerParameterRollTest.cpp` | `VoxelForge.Composer.ParameterRoll` | Asset-Registry corpus audit + complete per-archetype spread/exclusion/clamp table; asserts bit-identical deterministic rerolls and same-archetype parents; measures 64 transient candidate strates with `VF_MeasureStrate` plus the exact unsnapped arrival→departure law; brute-forces every rolled production box verdict. Current detail-enabled run: **59/64 survival (92.2%)**, **1,332 Mixed + 553 AllSolid + 675 AllAir = 1,228 proved boxes**, **1,634,468 lattice voxels checked, 0 violations**, 113.317 s total. Feature scale **0→376**; walkable **0.000000→0.388506**; all 17 TunnelNetwork/Underwater candidates carried live detail activation. |
+| `VoxelForgeComposerParameterRollTest.cpp` | `VoxelForge.Composer.ParameterRoll` | Asset-Registry corpus audit + complete per-archetype spread/exclusion/clamp table; asserts bit-identical deterministic rerolls and same-archetype parents; measures 64 transient candidate strates with `VF_MeasureStrate` plus the exact unsnapped arrival→departure law; brute-forces every rolled production box verdict. Bootstrap follow-up: **1,422 applications / 168 distinct fields**; **38/64 survival**, feature scale **0→376**, walkable **0.000000→0.286766** (no broadening beyond the prior run); **1,356 Mixed + 608 AllSolid + 596 AllAir = 1,204 proved boxes**, **1,602,524 lattice voxels checked, 0 violations**, 146.250 s total in the final full-namespace run. |
 | ″ | `VoxelForge.Composer.TerrainDetailLiveness` | Fixed 4,096-point `GetDensityAt` lattice, legacy and operator-stack paths; changes one terrain-detail group at a time with an empty terrain-op pool. Proves 9 live groups / 23 fields and 3 dead groups / 11 fields; all 24 rows match. |
-| `VoxelForgeComposerStructureRollTest.cpp` | `VoxelForge.Composer.StructureRoll` | Rolls root polarity → legal shape source → polarity-derived conversion → 4–8 declaration-legal modifiers → mandatory structural posts; blends the six native parameter families independently, measures 64 novel stacks, checks exact arrival→departure connectivity, rerolls every recipe/stack for determinism, and brute-forces every uniform box verdict. Focused run: **46/64 survival (71.9%)**, **64 distinct recipes**, **RoomGraph 15 / Lattice 19 / Shaft 8 / Island 14 / Noise 8**, **k=4:11 / 5:13 / 6:11 / 7:10 / 8:19**, **489 proved boxes / 650,859 voxels / 0 violations**. |
+| `VoxelForgeComposerStructureRollTest.cpp` | `VoxelForge.Composer.StructureRoll` | Rolls root polarity → legal shape source → polarity-derived conversion → 4–8 declaration-legal modifiers → mandatory structural posts; blends the six native parameter families independently, measures 64 novel stacks, captures the same grid for the deterministic XZ/XY preview, checks exact arrival→departure connectivity, rerolls every recipe/stack for determinism, and brute-forces every uniform box verdict. Focused run: **42/64 survival (65.6%)**, **64 distinct recipes**, **6,848 bootstrap applications / 107 distinct fields**, **659 proved boxes / 877,129 voxels / 0 violations**, **64 rendered pairs + index.html**. |
 | `VoxelForgeLayoutOrderIndependenceTest.cpp` | `VoxelForge.Determinism.LayoutOrderIndependence` | Builds a known transient soft-pointer pool, then rebuilds it in original, reversed, and swapped orders. Requires a non-empty layout and passage set, and compares every slot's definition/Z/height plus passage endpoints, radius, type, control geometry, and bounds bit-for-bit. |
 | `VoxelForgePassageOpenSpaceTest.cpp` | `VoxelForge.Determinism.PassageLandsInOpenSpace` | Uses the real fixture density path to check every generated inter-strate passage whose destination query answers: a 16-point ring outside the mouth's carve/blend band has at least half its samples in destination air, and the endpoint matches the pure open-point result within the mouth's float envelope. This is a connectivity proxy, not a flood-fill proof. Reports checked passages and false/unanswerable archetypes; fails if it inspects zero passages. |
 | `VoxelForgeStrateConnectivityTest.cpp` | `VoxelForge.Generation.StrateConnectivity` / `VoxelForge.Generation.StrateConnectivityRefinement` / `VoxelForge.Generation.VerticalShaftSeamFreedom` | Bounded strate metrics with density-polarity and solid-gap controls, deterministic route rechecks, and refinement sweeps. The refinement test fits the measurement AABB to each arrival/departure mouth pair, reports exact before/after seed-6 cell counts, reruns every negative with doubled margin, measures tree orphan candidates/path reachability and roughness-bubble proxies, asserts axis landings, checks source/mirror physical paths, and requires 16/16 effective arrival→departure results across the 16 VerticalShafts seeds. Margin-binding negatives are reported as measurement limits, never as gap findings. The seam test re-evaluates cell-boundary positions after warming distinct neighbouring chunk contexts in both legacy and operator-stack paths. |