Expand material support and checkpoint the completed building toolkit

Expose the runtime block/item registry through compact material search and
single-material descriptions. Preserve private block-entity data through
checked edits and durable undo without sending payloads to model context.

Include the completed terrain tools, isolated world/map plugin, station lift,
ACP streaming and guidance fixes, local camera auto-connect, construction
scripts, and their public documentation, references and verification records.
Active station decoration and private runtime data remain outside this commit.

Validation: 145 Maven tests, 47 Bridge tests, successful camera Gradle build,
and isolated Paper verification of all 1,196 block defaults plus 5,392
independent property cases for placement, same-material edits and restoration.

scripts/verify-layout-survey.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Compare every live map column to the planned visible result and inspect hidden water."""
+import argparse
+from collections import defaultdict
+import importlib.util
+import json
+from pathlib import Path
+
+ROOT=Path(__file__).resolve().parents[1]
+
+def main():
+    p=argparse.ArgumentParser(description=__doc__)
+    p.add_argument('--before',type=Path,required=True);p.add_argument('--after',type=Path,required=True)
+    p.add_argument('--layout',type=Path,action='append',required=True);p.add_argument('--report',type=Path,required=True)
+    args=p.parse_args();before=json.loads(args.before.read_text());after=json.loads(args.after.read_text())
+    for key in ('world_uuid','min_x','max_x','min_z','max_z','width','length'):
+        if before[key]!=after[key]:raise ValueError('Map scopes differ: '+key)
+    w=before['width'];expected_y=before['surface_y'].copy()
+    expected_m=[before['palette'][i] for i in before['material_index']]
+    original_m=expected_m.copy();targets=set();planned_blocks=0
+    for path in args.layout:
+        layout=json.loads(path.read_text())
+        if layout['scope']['world_id']!=before['world_uuid']:raise ValueError('Layout world differs')
+        for b in sorted(layout['blocks'],key=lambda b:b['y']):
+            i=(b['z']-before['min_z'])*w+b['x']-before['min_x'];targets.add((b['x'],b['y'],b['z']));planned_blocks+=1
+            if b['y']>=expected_y[i]:expected_y[i]=b['y'];expected_m[i]=b['block']
+    observed=[after['palette'][i] for i in after['material_index']]
+    mismatches=[i for i in range(len(expected_y)) if expected_y[i]!=after['surface_y'][i] or expected_m[i]!=observed[i]]
+    if mismatches:raise ValueError(f'{len(mismatches)} unexpected surface columns; first indices {mismatches[:8]}')
+    hidden_water=defaultdict(list)
+    for i,material in enumerate(original_m):
+        if material=='minecraft:water' and observed[i]!='minecraft:water':
+            x=i%w+before['min_x'];z=i//w+before['min_z'];y=before['surface_y'][i]
+            hidden_water[(x//16,z//16,y)].append((x,y,z))
+    spec=importlib.util.spec_from_file_location('terrain',ROOT/'scripts/terrain.py')
+    terrain=importlib.util.module_from_spec(spec);spec.loader.exec_module(terrain)
+    backend=terrain.Backend(ROOT/'.runtime/server/plugins/MinecraftBuilderMCP/config.yml')
+    context=backend.call('project_context')
+    if context['world_id']!=before['world_uuid']:raise ValueError('Live verification world differs')
+    verified_water=0
+    for points in hidden_water.values():
+        lo={axis:min(point[j] for point in points) for j,axis in enumerate(('x','y','z'))}
+        hi={axis:max(point[j] for point in points) for j,axis in enumerate(('x','y','z'))}
+        read=backend.call('region_inspect',min=lo,max=hi,detail='blocks')
+        states={tuple(b['pos'][axis] for axis in ('x','y','z')):b['state'] for b in read['blocks']}
+        for point in points:
+            if not states[point].startswith('minecraft:water['):raise ValueError('Water changed beneath a marker: '+str(point))
+            verified_water+=1
+    report={'world':before['world'],'source':'live Paper surface maps + bounded RPC water reads',
+            'verified_surface_columns':len(expected_y),'surface_mismatches':0,
+            'unique_marker_blocks':len(targets),'planned_writes':planned_blocks,
+            'original_water_columns':original_m.count('minecraft:water'),'water_columns_obscured_by_markers':verified_water,
+            'water_obscured_by_markers_verified_intact':True,
+            'height_unchanged_columns':sum(a==b for a,b in zip(before['surface_y'],after['surface_y'])),
+            'capture_started_at':after['capture_started_at'],'capture_finished_at':after['capture_finished_at'],
+            'atomic_snapshot':False,'note':'World edits were idle during each capture. Terrain follows its original heights; raised markers represent future structures, not finished traversable paths.'}
+    args.report.parent.mkdir(parents=True,exist_ok=True);args.report.write_text(json.dumps(report,indent=2)+'\n')
+    print(json.dumps(report))
+
+if __name__=='__main__':main()