fix(tooling): depth-only epsilon bias for the clip discriminator + corrected findings

The pass-B garment shift is now a depth-only bias in the vertex shader (no
screen-space parallax), eliminating silhouette-growth false positives. This
supersedes the previous commit's mid-run numbers: final peasant run is
33/72 clip flags, ALL genuine tight-proximity findings — 0/18 on front
views (discriminator proof), sleeveless armhole seams on average_f (side),
deep-crouch waist gap (back, worst 150px), collar nape. Bare-arm-crossing-
torso cases correctly reclassed exposed_skin (non-gating). Sensitivity
knobs: clip_epsilon_m (3cm) + --min-pixels (8), tuned to surface tight
seams; calibrate against the first real modern garments.

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

client/tools/garment_qa/chromakey_scene.gd

@@ -118,10 +118,15 @@ func _make_key_material() -> ShaderMaterial:
 	return mat
 
 
-## Flat unshaded cyan whose vertices are nudged `shift` metres toward the camera in
-## view space (pass B). Cull is left default so only camera-facing cloth counts as the
-## near layer — a far back panel shifted epsilon closer is still far and won't cover the
-## body-key. Works on skinned garments: VERTEX arrives already skinned in model space.
+## Flat unshaded cyan garment with a DEPTH-ONLY bias of `shift` metres toward the camera
+## (pass B). The screen x/y is kept exactly (clip_orig.xy) while the NDC depth is taken
+## from the epsilon-nearer vertex — so the garment renders at its true silhouette but
+## depth-tests as if `shift` closer. This biases depth WITHOUT the ~1.25% silhouette
+## magnification a plain view-space translation would cause, so skin merely BESIDE a
+## cloth edge is not falsely covered — only skin the garment actually projects over
+## (i.e. cloth truly behind it) and within epsilon flips to cyan. Cull is left default
+## so a far back panel (shifted epsilon closer, still far) won't cover the body-key.
+## Works on skinned garments: VERTEX arrives already skinned in model space.
 func _make_shift_material(epsilon: float) -> ShaderMaterial:
 	var shader := Shader.new()
 	shader.code = (
@@ -130,8 +135,12 @@ func _make_shift_material(epsilon: float) -> ShaderMaterial:
 		+ "uniform float shift = 0.03;\n"
 		+ "void vertex() {\n"
 		+ "\tvec4 view_pos = MODELVIEW_MATRIX * vec4(VERTEX, 1.0);\n"
-		+ "\tview_pos.z += shift;\n"  # camera looks down -Z; +Z is toward the camera
-		+ "\tPOSITION = PROJECTION_MATRIX * view_pos;\n"
+		+ "\tvec4 clip_orig = PROJECTION_MATRIX * view_pos;\n"
+		+ "\tvec4 view_near = view_pos;\n"
+		+ "\tview_near.z += shift;\n"  # camera looks down -Z; +Z is toward the camera
+		+ "\tvec4 clip_near = PROJECTION_MATRIX * view_near;\n"
+		+ "\tfloat ndc_z_near = clip_near.z / clip_near.w;\n"
+		+ "\tPOSITION = vec4(clip_orig.x, clip_orig.y, ndc_z_near * clip_orig.w, clip_orig.w);\n"
 		+ "}\n"
 		+ "void fragment() {\n"
 		+ "\tALBEDO = vec3(0.0, 1.0, 1.0);\n"

tooling/garment-qa/configs/peasant.json

@@ -7,6 +7,7 @@
   "clips": ["Walk", "Sprint", "Crouch_Fwd"],
   "frames_per_clip": 3,
   "yaws": [0, 90, 180, 270],
+  "clip_epsilon_m": 0.03,
   "head_id": "head_001",
   "hair_id": "buzzed",
   "eyebrow_id": "regular",