docs(lena): land pending stage-07 crotch-fill recipe

`07_fill_crotch.py` and its README autopsy were written in an earlier session
and had been sitting uncommitted. Committing them unchanged, separately from
today's hand-weight work, so neither is misattributed to the other.

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

characters/work/lena_leafbikini/README.md

@@ -28,6 +28,8 @@ of a 1.777 m body). Read-only, and re-hashed by every stage that opens it.
 | `03_render_leaves.py` | textured **and clay** turnaround of any mesh in the lane. The clay pass is what settled the question |
 | `04_leaf_mask.py` | builds and *proves* the leaf mask: hue key → component filter → close → hole fill → grow, baked to vertex colour and rendered |
 | `05_cut_leaves.py` | deletes the masked faces. Holes left open, on purpose |
+| `06_open_in_blender.py` | opens a lane mesh in the Blender GUI, framed on her front, Material Preview |
+| `07_fill_crotch.py` | **v02**: Barbie-fills the crotch — melts the briefs leaves into a smooth featureless surface, bust holes stay open. See below |
 
 ## What the leaves turned out to be
 
@@ -109,18 +111,63 @@ Stage 05's gates, all reported and the first two fatal:
 | surviving shells | 1 |
 | removed geometry's extent | z 0.455–0.755 of height (bust + briefs bands only) |
 
+## v02 — the Barbie crotch fill (stage 07)
+
+Target: "Barbie doll anatomy" — a completely smooth, undifferentiated pelvic surface, no
+cleft, no features, belly flowing into thighs. Jeremy's "take the distance and angle
+between the two sides" is precisely a bi-harmonic membrane: the rim supplies POSITION, the
+collar behind it supplies SLOPE through the second Laplacian application, and L²x = 0
+cannot invent detail. Bust holes stay cut open (v01 behaviour); only the briefs band gets
+the treatment.
+
+Getting there burned through roughly ten runs; the recipe header carries the full autopsy,
+the short version is:
+
+| attempt | verdict |
+|---|---|
+| triangle_fill the v01 holes + membrane | the briefs rim is ONE ~2,500-vert loop snaking front → between the legs → back; beauty triangulation bridges the WRONG BANKS at the bends, and the rim itself still carried leaf-root crumple the membrane faithfully anchored to |
+| + rim erosion + Delaunay flips + double solve | better rims, same disease — flips are local, the mis-bridging is global; sliver strands shot off the hips |
+| **melt instead of fill** (the pivot) | the leaf shell IS the disk that spans the hole — the scan's own manifold surface. Free its verts + a skin collar, solve; wrong-bank bridging becomes impossible. This produced the first genuinely smooth pelvis |
+| proudness detectors + deflation for the leftovers | fully-masked leaves are PENDANT BALLOONS — closed shells whose excess area the (no-maximum-principle) bi-harmonic parks as smooth raised caps. Smoothing-built references partially follow any bump wider than their radius, and **Taubin references are worse than useless here: shape-preserving by design, a 1.5 cm cap sits inside the passband and reads ~0** |
+| density excision + scar refill | catches the FLAT wads (the melted shell lies ~4 layers deep, and piles would z-fight) but not inflated caps, which sit BELOW the piled median. Scar refill needs: per-sweep densify scope with a floored target (a sliver scar once re-densified everything to 3.3M faces / 17 h), a slit weld first (scars meeting Tripo slits are ribbons, not loops — fill ops refuse them, and degenerate output crashed Blender once), and a >900-edge refusal |
+| occlusion / fin / diffusion detectors for the last four "caps" | all near-zero. A pixel-ray probe finally explained why: **the last bumps were not leaf debris at all — they are the melt web itself bridging taut over the inguinal hollow.** There was never skin under the vine, and every rim-anchored method spans its anchors by construction |
+| **+ the flow finish** (the guarantee) | damped pure-Laplacian flow over the whole changed region, no detector at all: the maximum principle sinks any pendant cap while the 5-10× wider pubic web barely moves. Ramp weight 0→1 over **3** rings — at 8 rings the hip-vine channel (10–20 rings wide) sat entirely in the damped zone |
+| **+ the solid-welt pass** | some leaf roots are SOLID skin-painted ridges, not shells — free them (0.5 mm proudness against a whole-band 400-sweep reference; honest skin reads p95 +0.13 mm) and re-solve locally; converges in 2 passes (5,375 verts, then 1) |
+
+Pipeline as shipped in `07_fill_crotch.py`: weld → cut bust open (+despike) → free briefs
+leaves + collar → remnant sweep (relaxed hue/blown-white key near the melt, no speckle
+filter) → bi-harmonic melt (matrix-free Jacobi-PCG, harmonic warm start) → solid-welt pass
+×2 → density excision of flat wads + occlusion pass → slit weld + degenerate dissolve →
+three scar-fill sweeps + patch solve → flow finish. Melted faces get one donor texel
+(thigh-band vertex nearest the band's median tone with the most neutral normal texel) —
+the atlas is Tripo chart soup, so interpolating UVs across the fill would sample garbage.
+
+```
+"$B" --background --factory-startup --python $L/07_fill_crotch.py -- \
+     characters/originals/female/female_lena_leafbikini_tripo.glb $L/leaf_mask.npz \
+     $L/v02/lena_leafbikini_crotchfill_sculpt_glb_v02.glb --free-rings 3
+```
+
 ## Open
 
-- **The holes are not filled, by request.** Filling is a separate and harder decision:
-  the crotch/gusset history in `work/lena/06*.py` is what happens when a membrane spans a
-  wide footprint — it flattens the anatomy it spans, which is why the nude lane only ever
-  faired a narrow rim band. Whatever fills these has to rebuild bust and crotch anatomy,
-  not just span them.
-- The base-colour map still carries the leaves and their baked contact shadows. The rim of
-  each hole is skin painted with leaf shadow, so it reads darker than her surrounding tone.
-- **The cut is unrigged**, because it was authored on the pristine original. It transfers
-  to the shipped body for free: `01_graft.py` moved the mesh 0.000000 mm, so
-  `lena_leafbikini_base_v01` carries the *same* 1,029,360 vertices in the same order and
-  `leaf_mask.npz` indexes it directly. Cutting the shipped GLB is running stage 05 with a
-  different first argument — but the result is a new ship folder, never an edit to the
-  frozen one.
+- **The hip-side shelf bulges are a known consequence, not a bug to chase further.** Where
+  the vine crossed the inguinal crease there was never skin underneath, and "take the
+  distance and angle between the two sides" — the membrane — spans its anchors by
+  construction. Any method anchored at the rims produces the same taut bridge (harmonic,
+  bi-harmonic, and flow all agree; the maximum principle *protects* a two-sided span).
+  Killing them means SCULPTING the crease through the strip — invented anatomy, its own
+  decision, its own stage. Ten runs of detector archaeology confirmed there is nothing
+  foreign left there to remove.
+- **The bust holes are not filled, by request** (v01 deliverable; v02 fills the crotch
+  only). Whatever fills the bust has to rebuild breast anatomy, not just span it — see
+  `tools/make_lena_nude_body.py` for how the nude lane sculpted hers procedurally.
+- The base-colour map still carries the leaves and their baked contact shadows. Around the
+  v01 holes and the v02 fill alike, the surviving skin reads darker than her surrounding
+  tone — an albedo re-author job for a later stage (the nude lane's harmonic refill is the
+  template).
+- **Both artifacts are unrigged**, because they were authored on the pristine original.
+  They transfer to the shipped body's frame for free: `01_graft.py` moved the mesh
+  0.000000 mm, so `lena_leafbikini_base_v01` carries the *same* 1,029,360 vertices in the
+  same order and `leaf_mask.npz` indexes either mesh. Re-running 05/07 against the shipped
+  GLB is a first-argument change — but the result is a new ship folder, never an edit to
+  the frozen one.