passages: memoized exact MC midpoints + wider conservative sweep bounds (L101, exact vs L100)

Off-grid census by caller (MC midpoints, skirts, far shells); all 63.0M sweep misses accounted
(1.9M exact-route fallbacks, 61.1M counted bound skips). Exact MC midpoint queries memoized by
float bits (Unreal enables it too); feature bounds expanded. L100/L101 whole-view hashes equal in
all four strata (v216 unchanged); 0 added/removed crossings; 15 capture pairs pixel-identical.
Near-ready @W12 L100 -> L101: FI 1.77 -> 1.65, TN 1.66 -> 1.54, SW 0.85 -> 0.84, VS 1.03 -> 1.03 s
(L98 2.28/2.23/1.02/1.11). Fast tier PASS; Linux UE host builds. Unreal arrival traces not obtained
(the runner wrongly applied the 6 GiB address-space cap to Unreal).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Research/WorldAssemblerM3/Linux101/RunL101Captures.py

@@ -0,0 +1,602 @@
+#!/usr/bin/env python3
+"""Capture matched L100/L101 passage mouth and mid-route views."""
+from __future__ import annotations
+
+import json
+import math
+import struct
+import subprocess
+import time
+import zlib
+from array import array
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[4]
+OUT = ROOT / "Saved/Linux/l101/captures"
+IMAGE_DIR = Path(__file__).resolve().parent / "captures"
+DATA = ROOT / "Standalone/data/owner_world.json"
+LAYOUT_PATH = ROOT / "Saved/Linux/l99/resolved-sw.json"
+BINARIES = {
+    "before-l100": ROOT / "Saved/Linux/l100/bin/VoxelForgeCoreHeadless-l100-clang",
+    "after-l101": ROOT / "Saved/Linux/l101/bin/VoxelForgeCoreHeadless-l101-clang",
+}
+RENDERER = ROOT / "Saved/Linux/l101/bin/VoxelForgeOffscreenCapture-l101-clang"
+VOXEL_Q = 256.0
+CORE_UM_PER_VOXEL = 250_000.0
+ROUTE_POINTS = {}
+ROUTE_LENGTHS = {}
+
+
+def add(a, b):
+    return tuple(x + y for x, y in zip(a, b))
+
+
+def sub(a, b):
+    return tuple(x - y for x, y in zip(a, b))
+
+
+def mul(a, s):
+    return tuple(x * s for x in a)
+
+
+def dot(a, b):
+    return sum(x * y for x, y in zip(a, b))
+
+
+def norm(a):
+    length = math.sqrt(dot(a, a))
+    if length < 1.0e-8:
+        raise ValueError("degenerate capture direction")
+    return tuple(x / length for x in a)
+
+
+def fmt(values):
+    return ",".join(f"{value:.9f}" for value in values)
+
+
+def angles(camera, target):
+    delta = sub(target, camera)
+    return (math.degrees(math.atan2(delta[0], delta[1])),
+            math.degrees(math.atan2(delta[2], math.hypot(delta[0], delta[1]))))
+
+
+def interpolate(points, distance):
+    remaining = max(0.0, distance)
+    for a, b in zip(points, points[1:]):
+        delta = sub(b[0], a[0])
+        length = math.sqrt(dot(delta, delta))
+        if length < 1.0e-8:
+            continue
+        if remaining <= length:
+            t = remaining / length
+            return (tuple(a[0][i] + delta[i] * t for i in range(3)),
+                    a[1] + (b[1] - a[1]) * t)
+        remaining -= length
+    return points[-1]
+
+
+def route_frame(points, distance):
+    center, radius = interpolate(points, distance)
+    before, _ = interpolate(points, max(0.0, distance - 0.25))
+    after, _ = interpolate(points, min(sum(
+        math.sqrt(dot(sub(b[0], a[0]), sub(b[0], a[0])))
+        for a, b in zip(points, points[1:])), distance + 0.25))
+    tangent = norm(sub(after, before))
+    horizontal = norm((tangent[0], tangent[1], 0.0))
+    side = (-horizontal[1], horizontal[0], 0.0)
+    return center, radius, tangent, side
+
+
+def route_length(points):
+    return sum(math.sqrt(dot(sub(b[0], a[0]), sub(b[0], a[0])))
+               for a, b in zip(points, points[1:]))
+
+
+def nearest_route(points, point):
+    best = None
+    distance_along = 0.0
+    for a, b in zip(points, points[1:]):
+        delta = sub(b[0], a[0])
+        length_sq = dot(delta, delta)
+        if length_sq < 1.0e-10:
+            continue
+        segment_length = math.sqrt(length_sq)
+        t = max(0.0, min(1.0, dot(sub(point, a[0]), delta) / length_sq))
+        center = add(a[0], mul(delta, t))
+        tangent = norm(delta)
+        radial = sub(point, center)
+        radial = sub(radial, mul(tangent, dot(radial, tangent)))
+        distance = math.sqrt(dot(sub(point, center), sub(point, center)))
+        if best is None or distance < best[0]:
+            radius = a[1] + (b[1] - a[1]) * t
+            best = (distance, center, tangent, radial, radius,
+                    distance_along + t * segment_length)
+        distance_along += segment_length
+    if best is None:
+        raise ValueError("passage route has no non-degenerate segment")
+    return best
+
+
+def run(name, command, headless):
+    log = OUT / f"{name}.log"
+    wrapped = ["taskset", "-c", "0-11"]
+    if headless:
+        wrapped += ["prlimit", "--as=6442450944", "--"]
+    wrapped += ["timeout", "1740s", *map(str, command)]
+    started = time.monotonic()
+    with log.open("w", encoding="utf-8") as stream:
+        result = subprocess.run(wrapped, cwd=ROOT, stdout=stream,
+                                stderr=subprocess.STDOUT, check=False, timeout=1745)
+    row = {"name": name, "exit_code": result.returncode,
+           "wall_s": round(time.monotonic() - started, 3),
+           "log": str(log.relative_to(ROOT))}
+    print("[L101CaptureRun] " + json.dumps(row, sort_keys=True), flush=True)
+    if result.returncode != 0:
+        raise RuntimeError(f"capture step failed: {name}; see {log}")
+    return row
+
+
+def nearest_surface_anchor(mesh, point, tile_search_margin_m=20.0):
+    """Return the nearest surface vertex and outward mesh normal from a VFMSH scene."""
+    best_distance_sq = float("inf")
+    best_position = best_normal = None
+    with mesh.open("rb") as stream:
+        magic = stream.read(8)
+        has_materials = magic == b"VFMSH002"
+        if magic not in (b"VFMSH001", b"VFMSH002"):
+            raise RuntimeError(f"unsupported mesh scene header: {mesh}")
+        version, voxel_um, tile_count = struct.unpack("<3I", stream.read(12))
+        if version != (2 if has_materials else 1):
+            raise RuntimeError(f"mesh scene version mismatch: {mesh}")
+        stream.seek(40, 1)  # stored camera position, yaw, and pitch
+        for _ in range(tile_count):
+            key = struct.unpack("<4i", stream.read(16))
+            surface_count, _, vertex_count, index_count, mask_count = struct.unpack(
+                "<5I", stream.read(20))
+            extent = (32 << key[3]) * voxel_um / 1_000_000.0
+            origin = (key[0] * extent, key[1] * extent, key[2] * extent)
+            if any(point[axis] < origin[axis] - tile_search_margin_m or
+                   point[axis] > origin[axis] + extent + tile_search_margin_m
+                   for axis in range(3)):
+                stream.seek(vertex_count * 24 + (10 * vertex_count if has_materials else 0)
+                            + index_count * 4 + mask_count, 1)
+                continue
+            positions = array("f")
+            positions.frombytes(stream.read(vertex_count * 12))
+            normals = array("f")
+            normals.frombytes(stream.read(vertex_count * 12))
+            if has_materials:
+                stream.seek(vertex_count * 10, 1)
+            stream.seek(index_count * 4 + mask_count, 1)
+            if struct.pack("=I", 1) != struct.pack("<I", 1):
+                positions.byteswap()
+                normals.byteswap()
+            for index in range(min(surface_count, vertex_count)):
+                offset = index * 3
+                # VFMSH stores vertex coordinates in world space; tile origin
+                # is metadata for edge rendering and must not be added again.
+                position = tuple(float(positions[offset + axis]) for axis in range(3))
+                delta = sub(position, point)
+                distance_sq = dot(delta, delta)
+                if distance_sq >= best_distance_sq:
+                    continue
+                raw_normal = tuple(float(normals[offset + axis]) for axis in range(3))
+                if dot(raw_normal, raw_normal) < 1.0e-10:
+                    continue
+                best_distance_sq = distance_sq
+                best_position = position
+                best_normal = norm(raw_normal)
+    if best_position is None:
+        raise RuntimeError(f"no nearby surface vertices in mesh scene: {mesh}")
+    return {"position_m": best_position, "normal": best_normal,
+            "distance_m": math.sqrt(best_distance_sq)}
+
+
+def make_passages(layout):
+    q_to_m = layout["core_voxel_size_um"] / (VOXEL_Q * 1_000_000.0)
+    passages = []
+    all_routes = []
+    for passage in layout["passages"]:
+        controls = [(tuple(float(q) * q_to_m for q in p["position_q"]),
+                     float(p["radius_q"]) * q_to_m)
+                    for p in passage["control_points"]]
+        upper = tuple(float(q) * q_to_m for q in passage["upper_mouth_q"])
+        lower = tuple(float(q) * q_to_m for q in passage["lower_mouth_q"])
+        ui = min(range(len(controls)), key=lambda i: dot(sub(controls[i][0], upper),
+                                                        sub(controls[i][0], upper)))
+        li = min(range(len(controls)), key=lambda i: dot(sub(controls[i][0], lower),
+                                                        sub(controls[i][0], lower)))
+        points = controls[ui:li + 1]
+        if len(points) < 2:
+            raise RuntimeError(f"invalid mouth path: {passage['stable_id']}")
+        upper_offset = math.sqrt(dot(sub(points[0][0], upper), sub(points[0][0], upper)))
+        lower_offset = math.sqrt(dot(sub(points[-1][0], lower), sub(points[-1][0], lower)))
+        length = route_length(points)
+        passage_views = []
+        for endpoint, distance, camera_distance, outward_sign in (
+                ("upper-mouth", 0.0, min(length, 7.4), -1.0),
+                ("lower-mouth", length, max(0.0, length - 5.5), 1.0)):
+            center, _, tangent, side = route_frame(points, distance)
+            camera_center, _, _, camera_side = route_frame(points, camera_distance)
+            camera = (camera_center[0] + camera_side[0] * 2.5,
+                      camera_center[1] + camera_side[1] * 2.5, camera_center[2])
+            outward = mul(tangent, outward_sign)
+            target = (center[0] + outward[0] * 8.0 + side[0] * 2.5,
+                      center[1] + outward[1] * 8.0 + side[1] * 2.5, center[2])
+            yaw, pitch = angles(camera, target)
+            passage_views.append({"name": f"{passage['stable_id']}-{endpoint}",
+                "kind": "mouth", "focus": center, "camera": camera, "target": target,
+                "yaw": yaw, "pitch": pitch, "clip": None, "fov": 80.0,
+                "focus_radius": 20.0, "passage": passage["stable_id"],
+                "camera_location": "passage-air"})
+        for fraction in (0.25, 0.50, 0.75):
+            distance = length * fraction
+            center, radius, _, side = route_frame(points, distance)
+            camera = (center[0] + side[0] * 0.75,
+                      center[1] + side[1] * 0.75,
+                      center[2] - radius + 1.6)
+            target_pos, target_radius = interpolate(
+                points, min(length, distance + 14.0))
+            target = (target_pos[0] + side[0] * 2.35,
+                      target_pos[1] + side[1] * 2.35,
+                      target_pos[2] - target_radius + 1.8)
+            yaw, pitch = angles(camera, target)
+            pct = int(round(fraction * 100))
+            passage_views.append({"name": f"{passage['stable_id']}-mid-{pct:02d}",
+                "kind": "mid-tunnel", "route_fraction": fraction,
+                "focus": center, "camera": camera, "target": target,
+                "yaw": yaw, "pitch": pitch, "clip": None,
+                "fov": 78.0, "focus_radius": 24.0,
+                "passage": passage["stable_id"]})
+        passages.append({"stable_id": passage["stable_id"], "route_length_m": length,
+                         "control_points": len(points), "upper_mouth_anchor_offset_m": upper_offset,
+                         "lower_mouth_anchor_offset_m": lower_offset, "views": passage_views})
+        all_routes.append((passage["stable_id"], points))
+    return passages, all_routes
+
+
+def make_hotspot_views(routes, reach_summary):
+    views = []
+    for series, rows, value_key, location_key, region_key in (
+        ("displacement", reach_summary["top_displacement_tiles"],
+         "max_displacement_cm", "displacement_location_metres", "displacement_region"),
+        ("normal", reach_summary["top_normal_tiles"],
+         "max_normal_degrees", "normal_location_metres", "normal_region"),
+    ):
+        for index, row in enumerate(rows, 1):
+            point = tuple(row[location_key])
+            candidates = [(nearest_route(route, point), name, route)
+                          for name, route in routes]
+            (distance, center, tangent, radial, radius, along), nearest_id, route = min(
+                candidates, key=lambda item: item[0][0])
+            if math.sqrt(dot(radial, radial)) < 0.25:
+                horizontal = norm((tangent[0], tangent[1], 0.0))
+                radial = (-horizontal[1], horizontal[0], 0.0)
+            outward = norm(radial)
+            camera = add(point, mul(outward, 20.0))
+            target = point
+            plane = None
+            yaw, pitch = angles(camera, target)
+            views.append({"name": f"top-{series}-{index:02d}", "kind": f"top-{series}",
+                "focus": point, "camera": camera, "target": target,
+                "yaw": yaw, "pitch": pitch, "clip": plane, "fov": 68.0,
+                "focus_radius": 18.0, "strate": row["strate"],
+                "value": row[value_key], "region": row[region_key],
+                "camera_anchor": "nearest-surface-l100-v1", "nearest_passage": nearest_id,
+                "route_distance_m": distance})
+    return views
+
+
+def decode_png(path):
+    """Decode 8-bit RGB/RGBA PNG pixels using only the Python standard library."""
+    data = path.read_bytes()
+    if data[:8] != b"\x89PNG\r\n\x1a\n":
+        raise RuntimeError(f"not a PNG: {path}")
+    width = height = bit_depth = color_type = interlace = None
+    compressed = bytearray()
+    offset = 8
+    while offset < len(data):
+        length = struct.unpack_from(">I", data, offset)[0]
+        kind = data[offset + 4:offset + 8]
+        chunk = data[offset + 8:offset + 8 + length]
+        if kind == b"IHDR":
+            width, height, bit_depth, color_type, compression, filtering, interlace = \
+                struct.unpack(">IIBBBBB", chunk)
+            if compression or filtering or interlace:
+                raise RuntimeError(f"unsupported PNG coding in {path}")
+        elif kind == b"IDAT":
+            compressed.extend(chunk)
+        elif kind == b"IEND":
+            break
+        offset += 12 + length
+    if bit_depth != 8 or color_type not in (2, 6):
+        raise RuntimeError(f"expected 8-bit RGB/RGBA PNG: {path}")
+    channels = 3 if color_type == 2 else 4
+    stride = width * channels
+    encoded = zlib.decompress(compressed)
+    pixels = bytearray(height * stride)
+    source_offset = 0
+    for y in range(height):
+        filter_type = encoded[source_offset]
+        source_offset += 1
+        row = bytearray(encoded[source_offset:source_offset + stride])
+        source_offset += stride
+        prior_offset = (y - 1) * stride
+        for index in range(stride):
+            left = row[index - channels] if index >= channels else 0
+            above = pixels[prior_offset + index] if y else 0
+            upper_left = pixels[prior_offset + index - channels] \
+                if y and index >= channels else 0
+            if filter_type == 1:
+                row[index] = (row[index] + left) & 255
+            elif filter_type == 2:
+                row[index] = (row[index] + above) & 255
+            elif filter_type == 3:
+                row[index] = (row[index] + ((left + above) >> 1)) & 255
+            elif filter_type == 4:
+                estimate = left + above - upper_left
+                left_distance = abs(estimate - left)
+                above_distance = abs(estimate - above)
+                upper_left_distance = abs(estimate - upper_left)
+                if left_distance <= above_distance and left_distance <= upper_left_distance:
+                    predictor = left
+                elif above_distance <= upper_left_distance:
+                    predictor = above
+                else:
+                    predictor = upper_left
+                row[index] = (row[index] + predictor) & 255
+            elif filter_type != 0:
+                raise RuntimeError(f"unsupported PNG filter {filter_type}: {path}")
+        start = y * stride
+        pixels[start:start + stride] = row
+    if channels == 3:
+        return width, height, pixels
+    rgb = bytearray(width * height * 3)
+    rgb[0::3] = pixels[0::4]
+    rgb[1::3] = pixels[1::4]
+    rgb[2::3] = pixels[2::4]
+    return width, height, rgb
+
+
+def image_geometry_metrics(path):
+    width, height, rgb = decode_png(path)
+    color_counts = {}
+    for offset in range(0, len(rgb), 3):
+        color = (rgb[offset], rgb[offset + 1], rgb[offset + 2])
+        color_counts[color] = color_counts.get(color, 0) + 1
+    total = width * height
+    visible = total - max(color_counts.values())
+    return {"width": width, "height": height, "unique_rgb": len(color_counts),
+            "visible_geometry_pixels": visible,
+            "visible_geometry_fraction": visible / total}
+
+
+def changed_pixel_count(before, after):
+    before_width, before_height, before_rgb = decode_png(before)
+    after_width, after_height, after_rgb = decode_png(after)
+    if (before_width, before_height) != (after_width, after_height):
+        raise RuntimeError(f"capture dimensions differ: {before} / {after}")
+    return sum(before_rgb[offset] != after_rgb[offset]
+               or before_rgb[offset + 1] != after_rgb[offset + 1]
+               or before_rgb[offset + 2] != after_rgb[offset + 2]
+               for offset in range(0, len(before_rgb), 3))
+
+
+def mesh_triangle_count(mesh):
+    with mesh.open("rb") as stream:
+        magic = stream.read(8)
+        has_materials = magic == b"VFMSH002"
+        if magic not in (b"VFMSH001", b"VFMSH002"):
+            raise RuntimeError(f"unsupported mesh scene header: {mesh}")
+        version, _, tile_count = struct.unpack("<3I", stream.read(12))
+        if version != (2 if has_materials else 1):
+            raise RuntimeError(f"mesh scene version mismatch: {mesh}")
+        stream.seek(40, 1)
+        triangles = 0
+        for _ in range(tile_count):
+            stream.seek(16, 1)
+            _, _, vertex_count, index_count, mask_count = struct.unpack(
+                "<5I", stream.read(20))
+            triangles += index_count // 3
+            stream.seek(vertex_count * 24 + (10 * vertex_count if has_materials else 0)
+                        + index_count * 4 + mask_count, 1)
+    return triangles
+
+
+def set_route_station(view, distance):
+    points = ROUTE_POINTS[view["passage"]]
+    length = ROUTE_LENGTHS[view["passage"]]
+    center, radius, _, side = route_frame(points, distance)
+    camera = (center[0] + side[0] * 0.75,
+              center[1] + side[1] * 0.75,
+              center[2] - radius + 1.6)
+    target_pos, target_radius = interpolate(points, min(length, distance + 14.0))
+    target = (target_pos[0] + side[0] * 2.35,
+              target_pos[1] + side[1] * 2.35,
+              target_pos[2] - target_radius + 1.8)
+    yaw, pitch = angles(camera, target)
+    if "route_fraction_requested" not in view:
+        view["route_fraction_requested"] = view["route_fraction"]
+        view["route_requested_focus"] = view["focus"]
+    view["route_fraction"] = distance / length
+    view["route_station_adjustment_m"] = distance - length * view["route_fraction_requested"]
+    view["focus"] = center
+    view["camera"] = camera
+    view["target"] = target
+    view["yaw"], view["pitch"] = yaw, pitch
+    view["clip"] = None
+
+
+def render_command(view, mesh, image, camera, yaw, pitch):
+    args = [RENDERER, mesh, image,
+        "--size=1600x900", f"--fov-deg={view['fov']:.1f}",
+        f"--camera-m={fmt(camera)}", f"--yaw-deg={yaw:.6f}",
+        f"--pitch-deg={pitch:.6f}", "--shade=readable", "--headlamp=on",
+        "--height-tint=on", "--tile-edges=off", "--tile-skirts=off",
+        f"--height-center-m={view['focus'][2]:.6f}", "--height-range-m=10",
+        f"--focus-region={fmt((*view['focus'], view['focus_radius']))}"]
+    if view["clip"] is not None:
+        args.append(f"--clip-plane={fmt(view['clip'])}")
+    return args
+
+
+def export_scene(view, binary, mesh, stem):
+    camera = view["camera"]
+    yaw, pitch = angles(camera, view["target"])
+    export_args = [binary, DATA, "--world-assembler-prototype", "--stream-benchmark",
+        "--stream-pipeline", "--workers=8", "--force-generate", "--clip-radius=3",
+        "--max-clip-level=0", "--max-level=0", "--render-distance-chunks=0",
+        f"--camera={fmt((*camera, yaw, pitch))}", f"--mesh-export={mesh}"]
+    row = run(f"{stem}-export", export_args, headless=True)
+    row["scene_bytes"] = mesh.stat().st_size if mesh.exists() else 0
+    row["scene_triangles"] = mesh_triangle_count(mesh) if row["scene_bytes"] else 0
+    return row
+
+
+def export_and_render(view, label, binary):
+    safe = view["name"].replace("/", "-")
+    stem = f"{safe}-{label}"
+    mesh = OUT / f"{stem}.vfmesh"
+    image = IMAGE_DIR / f"{safe}-{label}.png"
+    camera = view["camera"]
+    yaw, pitch = angles(camera, view["target"])
+    export_row = export_scene(view, binary, mesh, stem)
+    if export_row["scene_bytes"] <= 0:
+        raise RuntimeError(f"empty mesh scene: {mesh}")
+    if export_row["scene_triangles"] == 0:
+        if label != "before-l100" or view.get("kind") != "mid-tunnel":
+            raise RuntimeError(f"route station exports no surface triangles: {mesh}")
+        points = ROUTE_POINTS[view["passage"]]
+        length = ROUTE_LENGTHS[view["passage"]]
+        requested_fraction = view["route_fraction"]
+        requested_distance = length * requested_fraction
+        found_surface = False
+        for offset in (5.0, -5.0, 10.0, -10.0, 20.0, -20.0, 35.0, -35.0,
+                       50.0, -50.0, 75.0, -75.0, 100.0, -100.0, 150.0,
+                       -150.0, 200.0, -200.0):
+            distance = max(0.0, min(length, requested_distance + offset))
+            if distance == requested_distance:
+                continue
+            set_route_station(view, distance)
+            adjusted_stem = f"{stem}-station-{view['route_fraction']:.5f}"
+            export_row = export_scene(view, binary, mesh, adjusted_stem)
+            if export_row["scene_triangles"] > 0:
+                view["camera_anchor"] = "route-station-shifted-to-nearby-geometry"
+                found_surface = True
+                break
+        if not found_surface:
+            raise RuntimeError(f"no geometry along nearby route stations: {mesh}")
+        camera = view["camera"]
+        yaw, pitch = angles(camera, view["target"])
+    if label == "before-l100" and view.get("camera_anchor") == "nearest-surface-l100-v1":
+        anchor = nearest_surface_anchor(mesh, view["focus"], tile_search_margin_m=256.0)
+        camera = add(anchor["position_m"], mul(anchor["normal"], 8.0))
+        view["camera"] = camera
+        view["target"] = anchor["position_m"]
+        view["yaw"], view["pitch"] = angles(camera, view["target"])
+        view["clip"] = None
+        view["surface_anchor"] = anchor
+        yaw, pitch = view["yaw"], view["pitch"]
+    render_args = render_command(view, mesh, image, camera, yaw, pitch)
+    try:
+        render_row = run(f"{stem}-render", render_args, headless=True)
+    except RuntimeError:
+        if view["clip"] is None:
+            raise
+        retry_args = [arg for arg in render_args
+                      if not (isinstance(arg, str) and arg.startswith("--clip-plane="))]
+        render_row = run(f"{stem}-render-no-clip-retry", retry_args, headless=True)
+        render_row["clip_fallback"] = True
+    render_row["image"] = str(image.relative_to(ROOT))
+    render_row["image_bytes"] = image.stat().st_size if image.exists() else 0
+    if render_row["image_bytes"] <= 0:
+        raise RuntimeError(f"empty image: {image}")
+    geometry = image_geometry_metrics(image)
+    if label == "before-l100" and (
+            geometry["visible_geometry_pixels"] < 3000 or geometry["unique_rgb"] < 2):
+        # At a few deep route stations the default forward view looks into empty
+        # sky. Keep the camera on the route station and aim at the nearest L98
+        # surface in the exported scene; retain that matched target for L101.
+        anchor = nearest_surface_anchor(mesh, view["focus"], tile_search_margin_m=256.0)
+        if anchor["distance_m"] > 60.0:
+            raise RuntimeError(f"no nearby surface for fallback camera: {image} {anchor}")
+        camera = view["camera"]
+        target = anchor["position_m"]
+        yaw, pitch = angles(camera, target)
+        view["target"] = target
+        view["yaw"], view["pitch"] = yaw, pitch
+        view["clip"] = None
+        view["camera_anchor"] = "route-station-nearest-surface-target"
+        view["surface_anchor"] = anchor
+        retry_args = render_command(view, mesh, image, camera, yaw, pitch)
+        render_row = run(f"{stem}-render-surface-fallback", retry_args, headless=True)
+        render_row["image"] = str(image.relative_to(ROOT))
+        render_row["image_bytes"] = image.stat().st_size if image.exists() else 0
+        geometry = image_geometry_metrics(image)
+    render_row["geometry"] = geometry
+    if geometry["visible_geometry_pixels"] < 3000 or geometry["unique_rgb"] < 2:
+        raise RuntimeError(f"camera sees sky only or too little geometry: {image} {geometry}")
+    mesh.unlink()
+    return export_row, render_row
+
+
+def main():
+    OUT.mkdir(parents=True, exist_ok=True)
+    IMAGE_DIR.mkdir(parents=True, exist_ok=True)
+    for path in (*BINARIES.values(), RENDERER, DATA, LAYOUT_PATH):
+        if not path.is_file():
+            raise SystemExit(f"missing input: {path}")
+    layout = json.loads(LAYOUT_PATH.read_text(encoding="utf-8"))
+    passages, routes = make_passages(layout)
+    ROUTE_POINTS.clear()
+    ROUTE_LENGTHS.clear()
+    for stable_id, points in routes:
+        ROUTE_POINTS[stable_id] = points
+        ROUTE_LENGTHS[stable_id] = route_length(points)
+    views = [view for passage in passages for view in passage["views"]]
+    partial_path = OUT / "runs-partial.json"
+    existing_records = {}
+    if partial_path.is_file():
+        for item in json.loads(partial_path.read_text(encoding="utf-8")):
+            existing_records[item["view"]["name"]] = item
+    records = []
+    for view in views:
+        prior = existing_records.get(view["name"])
+        camera_matches = (prior is not None and
+                          prior["view"].get("camera_anchor") == view.get("camera_anchor"))
+        if camera_matches:
+            for key in ("camera", "target", "yaw", "pitch", "clip", "surface_anchor"):
+                if key in prior["view"]:
+                    view[key] = prior["view"][key]
+        if camera_matches and all(version in prior and
+                         (ROOT / prior[version]["render"]["image"]).is_file()
+                         for version in BINARIES):
+            records.append(prior)
+            print(f"[L101CaptureSkip] complete_pair={view['name']}", flush=True)
+            continue
+        pair = {"view": view}
+        for label, binary in BINARIES.items():
+            export_row, render_row = export_and_render(view, label, binary)
+            pair[label] = {"export": export_row, "render": render_row}
+            (OUT / "runs-partial.json").write_text(json.dumps(records + [pair], indent=2) + "\n",
+                                                   encoding="utf-8")
+        pair["comparison"] = {"changed_pixels": changed_pixel_count(
+            ROOT / pair["before-l100"]["render"]["image"],
+            ROOT / pair["after-l101"]["render"]["image"])}
+        (OUT / "runs-partial.json").write_text(json.dumps(records + [pair], indent=2) + "\n",
+                                               encoding="utf-8")
+        records.append(pair)
+    summary = {"source_layout_identity": layout["stable_identity"],
+        "view_count": len(views), "paired_png_count": len(views) * 2,
+        "passages": passages, "views": records}
+    (OUT / "summary.json").write_text(json.dumps(summary, indent=2) + "\n",
+                                      encoding="utf-8")
+    print("[L101CaptureSummary] " + json.dumps({
+        "views": len(views), "paired_png_count": len(views) * 2,
+        "images": [row[version]["render"]["image"] for row in records
+                   for version in BINARIES]}, sort_keys=True), flush=True)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())