feat(skirt-weights): inner-front anchor + import cache-bust

SKIRT_ANCHOR_IFP: pins the front-inner band of a garment to its thigh at
W=1.0 (asymmetric sector: 100deg inner / 135deg outer so back cloth never
pins to the thigh front) — the stitch answer to colliders being unable to
move strand root joints (probe-measured 32mm penetration at full stride).

save() now stamps asset.extras.skirt_weights_rev every run: weight-only
rewrites left the .gltf byte-identical, Godot's source_md5 check skipped
the reimport, and engines ran STALE weights (cost 2026-08-20 afternoon).

clothing/skirt_garment_weights.py

@@ -46,6 +46,7 @@ import math
 import os
 import struct
 import sys
+import time
 
 HERE = os.path.dirname(os.path.abspath(__file__))
 ANIM_ROOT = os.path.dirname(HERE)
@@ -139,6 +140,32 @@ PANTS_FROM = _envf("SKIRT_PANTS_FROM", 0.0)
 TUBE = os.environ.get("SKIRT_FOLLOW_TUBE") == "1"
 TUBE_FRONT = _envf("SKIRT_TUBE_FRONT", 45.0)   # half-angle of the full-follow front sector, degrees
 TUBE_BACK = _envf("SKIRT_TUBE_BACK", 0.25)     # follow multiplier directly behind the leg
+# INNER-FRONT ANCHOR (2026-08-20, Ozan watching the male run: "the front pugu can
+# go UNDER the balls — attach the clothing to the blue dots' furthest points;
+# as legs move, cloth stretches freely"). Push-only colliders can never stop the
+# panel sliding under the pusher balls — attachment can. The front panel's
+# front-INNER band (the diagonal the InnerFrontPush_* colliders ride) is pinned
+# to its thigh at SKIRT_ANCHOR_W, so the advancing leg CARRIES its cloth and
+# only the span between the two anchored bands stays spring-driven (the stretch
+# membrane). Requires SKIRT_FOLLOW_TUBE=1 (the anchor sector keys off tube_fwd).
+ANCHOR = os.environ.get("SKIRT_ANCHOR_IFP") == "1"
+ANCHOR_W = _envf("SKIRT_ANCHOR_W", 1.0)        # pin strength at the sector center
+ANCHOR_TOP = _envf("SKIRT_ANCHOR_TOP", 0.04)   # band, fraction of cloth drop
+ANCHOR_BOT = _envf("SKIRT_ANCHOR_BOT", 0.58)
+ANCHOR_FADE = _envf("SKIRT_ANCHOR_FADE", 0.06) # vertical edge fade (no hard step)
+ANCHOR_FRONT = _envf("SKIRT_ANCHOR_FRONT", 0.90)  # diagonal mix — matches SKIRT_IFP_*
+ANCHOR_INNER = _envf("SKIRT_ANCHOR_INNER", 0.45)
+# 2026-08-20 Ozan: "two legs work independently — stitch the cloth to the balls'
+# outer direction" + "the cloth trying to make an inner curve shows body —
+# disable it". Sector widened 55°→80°: each leg's whole front quadrant rides its
+# thigh rigidly; only the narrow midline strip stays spring (the stretch zone).
+ANCHOR_SECTOR = _envf("SKIRT_ANCHOR_SECTOR", 100.0)  # half-angle toward INNER, degrees
+# Probe finding (2026-08-20): the strand-top penetrations drive the panel's top
+# OUTER corners (110–135° from the diagonal — the hip/outer-front cloth), which
+# the symmetric sector rejected; those corners are what slid under the flexed
+# thigh. The outer side gets a wider gate; the inner side stays narrower so
+# BACK-flap verts (147°+ from the diagonal) are never pinned to the thigh front.
+ANCHOR_SECTOR_OUTER = _envf("SKIRT_ANCHOR_SECTOR_OUTER", 135.0)
 # Azimuth spread, in strand-gap units (2026-08-19, long tifi): the classic
 # 2-strand linear blend makes the hem fold PIECEWISE-LINEAR — mid-stride the
 # tube creases into a hard triangle where the front-leg cloth meets the
@@ -253,6 +280,12 @@ class Gltf:
 
     def save(self):
         self.d["buffers"][0]["byteLength"] = len(self.buf)
+        # CACHE-BUST (2026-08-20, cost an afternoon): weight-only rewrites leave the
+        # .gltf byte-identical → Godot's source_md5 check skips the reimport and the
+        # engine keeps running STALE weights. Stamp a changing extras token so the
+        # md5 moves every run and the importer always picks the new .bin up.
+        self.d.setdefault("asset", {})["extras"] = {
+            "skirt_weights_rev": time.time_ns()}
         with open(self.bin_path, "wb") as f:
             f.write(self.buf)
         with open(self.path, "w") as f:
@@ -413,7 +446,7 @@ def main():
         f"cloth hangs {span:.3f} below the ring top")
 
     out_j, out_w = [], []
-    stats = {"waistband": 0, "follow_sum": 0.0}
+    stats = {"waistband": 0, "follow_sum": 0.0, "anchored": 0}
     per_strand = {k: 0.0 for k in body_ring}
     thigh_total = 0.0
 
@@ -541,7 +574,39 @@ def main():
                              (slot["thigh_l"], (1.0 - pelvis_w) * f_l),
                              (slot["thigh_r"], (1.0 - pelvis_w) * (1.0 - f_l))):
                     w[j] = w.get(j, 0.0) + x * pants_mix
+            # ── inner-front anchor strength for this vertex (0 = free cloth) ──
+            anchor = 0.0
+            if (ANCHOR and tube_fwd is not None and near is not None
+                    and radial is not None and ANCHOR_TOP <= t <= ANCHOR_BOT):
+                rl = math.hypot(radial[0], radial[1])
+                if rl > 1e-6:
+                    sign_l = 1.0 if origin["thigh_l"][0] >= pelvis[0] else -1.0
+                    inner_x = -sign_l if near == "thigh_l" else sign_l
+                    dx = tube_fwd[0] * ANCHOR_FRONT + inner_x * ANCHOR_INNER
+                    dz = tube_fwd[1] * ANCHOR_FRONT
+                    dn = math.hypot(dx, dz)
+                    if dn > 1e-6:
+                        cos_d = (radial[0] * dx + radial[1] * dz) / (rl * dn)
+                        # Signed side of the diagonal: inner vs outer (mirrored
+                        # per leg — inner_x flips the 2D cross sign).
+                        cross = dx * radial[1] - dz * radial[0]
+                        lim = (ANCHOR_SECTOR if cross * (-inner_x) > 0.0
+                               else ANCHOR_SECTOR_OUTER)
+                        cos_sec = math.cos(math.radians(lim))
+                        if cos_d > cos_sec:
+                            af = smoothstep((cos_d - cos_sec) / max(1e-6, 1.0 - cos_sec))
+                            vf = (smoothstep((t - ANCHOR_TOP) / ANCHOR_FADE)
+                                  * (1.0 - smoothstep((t - (ANCHOR_BOT - ANCHOR_FADE))
+                                                      / ANCHOR_FADE)))
+                            anchor = ANCHOR_W * af * vf
             strand_scale = 1.0 - pants_mix
+            if ANCHOR and anchor > 0.0:
+                # Rigid pin of the front-inner band to its thigh; the ring keeps
+                # only what's left, so the panel between the bands is the stretch
+                # membrane (Ozan 2026-08-20).
+                w[slot[near]] = w.get(slot[near], 0.0) + anchor * strand_scale
+                stats["anchored"] += 1
+                strand_scale *= 1.0 - anchor
             if PANTS_SOLID4 and pants_mix > 0.0:
                 # exactly ONE strand bone: nearest strand by azimuth, its
                 # height-matched segment — total influence count stays at 4.
@@ -605,6 +670,9 @@ def main():
     log(f"waistband (pelvis only): {stats['waistband']} verts")
     log(f"mean thigh follow on panel verts: "
         f"{stats['follow_sum'] / max(1, n - stats['waistband']):.3f}")
+    if ANCHOR:
+        log(f"inner-front anchor: {stats['anchored']} verts pinned "
+            f"(band {ANCHOR_TOP:.2f}–{ANCHOR_BOT:.2f}, W={ANCHOR_W:.2f})")
     log("per-strand ring weight (must be non-zero everywhere):")
     for k in sorted(per_strand):
         peak = max(per_strand.values())