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

fable-idea.md

@@ -91,7 +91,14 @@ tiles.) In a tall multi-strate world most chunks in the desired set are full bed
 
 ### A. Tooling first — force multipliers for everything after
 
-**F1 — 2D world-preview editor tool.** ★ my top pick. An editor utility that samples `f_XY` (terrain height, relief M, water mask — later the biome map) over an N×N window into a `UTexture2D`, with the Surface|Macro knobs live. Tuning ReliefStrength/biome layout becomes seconds instead of regen-and-fly. Directly addresses the standing "hard to dial blind" pain (Worm passages, today's Stage 0 knobs). Extend with a top-view passage-path overlay (the data exists in `bDebugDrawPassages`).
+**F1 — 2D world-preview editor tool. ✅ BUILT 2026-09-04 (measurement + preview).** ★ my top pick. The
+editor/automation pass captures the exact coarse measurement grid, writes deterministic PNG XZ and
+XY slices plus a self-contained 64-candidate contact sheet, and labels walkable cells, scale, metric
+windows, rejection reasons, and the 2D-connectivity caveat. Output is under
+`Saved/ComposerPreview/<runid>/`; no runtime generation path is involved. The original idea remains:
+sample `f_XY` (terrain height, relief M, water mask — later the biome map) over an N×N window with
+the Surface|Macro knobs live, then extend with a top-view passage-path overlay (the data exists in
+`bDebugDrawPassages`).
 
 **F2 — Determinism validator button.** ✅ DONE 2026-07-04 (`AVoxelWorld::ValidateDeterminism`,
 Live Edit category). CallInEditor: sample a band of densities from two different chunk-window alignments, diff, report max delta. Turns the scariest invariant (§8.4 — window invariance) into a one-click regression test *before* biome code starts landing.