fix(client): cutaway cuts the camera-character sightline corridor, not a proximity dome (T-1088)

Live-session finding: the half-disc cut bit nearby side walls while leaving
the wall actually occluding the character at full height, with dome-contour
scallops across the two-row walls. Rewritten as a sightline corridor: walls
within CUT_CORRIDOR_HALF_W of the character's x, camera-side, out to a
pitch-derived reach (WALL_H / tan(pitch) — how far a wall can still occlude
in ortho; ~4.3 m at -30, breathes with the T-cycle tilt) drop to the stub.
FollowCamera3D exposes pitch_deg(); reach clamped 0.5-16 m.

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

client/shaders/sandbox/greybox_wall_cutaway.gdshader

@@ -5,33 +5,34 @@ render_mode diffuse_lambert, specular_disabled;
 // proto-production.
 //
 // COLOR-multiplied albedo (same four-state tint contract as the floor shader)
-// plus a smoothstep height cut: a half-disc of camera-side wall around the
-// character drops to a CUT_HEIGHT stub with smooth radial falloff — the
-// Xenonauts read, minus per-building logic the greybox doesn't have. The
-// cutaway cuts RENDER HEIGHT; the tint gates KNOWLEDGE — independent factors,
-// so remembered walls can be cut too (the player's camera doesn't care what the
-// character currently sees). Open box tops are acceptable greybox fidelity;
-// ghost band / dither / capping are named polish on this same shader.
+// plus a smoothstep height cut along the CAMERA->CHARACTER SIGHTLINE CORRIDOR:
+// walls inside the corridor drop to a CUT_HEIGHT stub — the Xenonauts read,
+// aligned to what actually occludes the character (the earlier proximity dome
+// bit side walls while leaving the occluding wall standing). The cutaway cuts
+// RENDER HEIGHT; the tint gates KNOWLEDGE — independent factors, so remembered
+// walls can be cut too. Open box tops are acceptable greybox fidelity; ghost
+// band / dither / capping are named polish on this same shader.
 //
-// u_char_pos_xz is the rig's INTERPOLATED world XZ, pushed once per frame
-// (GreyboxWorld.set_cutaway_char_pos) — the cut zone glides with the character,
-// so spatial smoothstep becomes temporal smoothness. Parked far away by default:
-// no cut until the first push.
+// Corridor geometry (world space — the camera has yaw 0 and looks world -Z;
+// the diamond view is WorldRoot's 45 deg rotation, never the camera's, D-148):
+// the ground projection of the camera->character sightline is the +Z half-line
+// at the character's x. A wall occludes the character only within
+// |to_wall.x| < corridor half-width AND 0 < to_wall.y < reach, where reach is
+// pitch-derived (a WALL_H wall can occlude someone at most WALL_H / tan(pitch)
+// away in ortho): ~4.3 m at the -30 deg gameplay preset, long at -5 frontal,
+// near-zero at -80 overhead. u_char_pos_xz + u_cut_reach are pushed per frame
+// (GreyboxWorld.set_cutaway_char_pos) so the corridor glides with the character
+// and breathes with the tilt. Parked far away by default: no cut until pushed.
 //
-// Camera-side predicate: the camera has yaw 0 and looks world -Z (the diamond
-// view is WorldRoot's 45 deg rotation, never the camera's — D-148), so camera
-// ground-forward is the constant vec2(0, -1) in world space. A wall fragment
-// sits between camera and character when to_wall.y > 0; the test runs in world
-// space, so it stays correct under the WorldRoot rotation.
-//
-// Geometry uniforms default to the SandboxConstants values; GreyboxWorld pushes
+// Static uniforms default to the SandboxConstants values; GreyboxWorld pushes
 // them at material build so SandboxConstants stays the single source (§12).
 
 uniform vec2 u_char_pos_xz = vec2(1000000.0, 1000000.0);
-uniform float u_wall_h = 2.5;       // SandboxConstants.WALL_H
-uniform float u_cut_height = 0.75;  // SandboxConstants.CUT_HEIGHT — the stub
-uniform float u_cut_radius = 5.0;   // SandboxConstants.CUT_RADIUS — half-disc radius
-uniform float u_cut_band = 1.5;     // SandboxConstants.CUT_BAND — radial falloff band
+uniform float u_wall_h = 2.5;            // SandboxConstants.WALL_H
+uniform float u_cut_height = 0.75;       // SandboxConstants.CUT_HEIGHT — the stub
+uniform float u_corridor_half_w = 1.4;   // SandboxConstants.CUT_CORRIDOR_HALF_W
+uniform float u_cut_band = 0.75;         // SandboxConstants.CUT_BAND — falloff band
+uniform float u_cut_reach = 4.4;         // per-frame: WALL_H / tan(camera pitch)
 uniform vec3 u_base_albedo : source_color = vec3(0.66, 0.64, 0.60);
 
 varying vec3 v_world_pos;
@@ -43,12 +44,13 @@ void vertex() {
 
 void fragment() {
     vec2 to_wall = v_world_pos.xz - u_char_pos_xz;
-    // Soft camera-side gate: fully cut from 0.75 m on the camera side of the
-    // character, fully solid from 0.25 m on the far side — no hard seam.
-    float side_f = smoothstep(-0.25, 0.75, to_wall.y);
-    // Radial falloff: full cut inside (radius - band), fading to none at radius.
-    float rad_f = 1.0 - smoothstep(u_cut_radius - u_cut_band, u_cut_radius, length(to_wall));
-    float allowed = mix(u_wall_h, u_cut_height, side_f * rad_f);
+    // Lateral gate: full cut inside (half_w - band), fading to none at half_w.
+    float lateral = 1.0 - smoothstep(u_corridor_half_w - u_cut_band, u_corridor_half_w, abs(to_wall.x));
+    // Near gate: soft start just behind the character (no hard seam at their feet).
+    float near_f = smoothstep(-0.25, 0.75, to_wall.y);
+    // Far gate: corridor ends where a WALL_H wall can no longer occlude.
+    float far_f = 1.0 - smoothstep(u_cut_reach, u_cut_reach + u_cut_band, to_wall.y);
+    float allowed = mix(u_wall_h, u_cut_height, lateral * near_f * far_f);
     if (v_world_pos.y > allowed) {
         discard;
     }