Expand voxel gameplay, lighting, full-height streaming and world imports

Add shared Rust/WASM physics, worker meshing and diagnostics, 64-chunk full-height streaming, atlas texture support, and baseline world import. Document the current implementation and include the supplied in-game lobby screenshot.

scripts/measure_physics.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+"""Measure factual Java 26.2 movement through a pinned local official runtime.
+
+Requires the cache prepared by catalog_generate.py and an existing Java 25 JDK.
+Does not download assets or start a Minecraft server. See measurement_scope in
+the generated fixture for the precise boundary of the original-runtime probe.
+"""
+from pathlib import Path
+import argparse
+import hashlib
+import json
+import os
+import subprocess
+import zipfile
+
+ROOT = Path(__file__).resolve().parents[1]
+SOURCE_SHA1 = "823e2250d24b3ddac457a60c92a6a941943fcd6a"
+
+
+def digest(path, algorithm="sha256"):
+    with path.open("rb") as source:
+        return hashlib.file_digest(source, algorithm).hexdigest()
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--java", type=Path, required=True)
+    parser.add_argument("--cache", type=Path, default=ROOT / "artifacts/catalog-cache")
+    parser.add_argument("--output", type=Path, default=ROOT / "artifacts/catalog-cache/physics-reference.json")
+    args = parser.parse_args()
+    cache = args.cache.resolve()
+    source = cache / "server.jar"
+    if digest(source, "sha1") != SOURCE_SHA1:
+        raise SystemExit("The official source JAR does not match the pinned Java 26.2 hash")
+    executable = cache / "versions/26.2/server-26.2.jar"
+    with zipfile.ZipFile(source) as bundle:
+        with bundle.open("META-INF/versions/26.2/server-26.2.jar") as embedded:
+            expected = hashlib.file_digest(embedded, "sha256").hexdigest()
+    if digest(executable) != expected:
+        raise SystemExit("The cached executable differs from the verified official bundle")
+    classpath = os.pathsep.join(map(str, [executable, *sorted((cache / "libraries").rglob("*.jar"))]))
+    java = args.java.resolve()
+    script = ROOT / "scripts/physics_reference.java"
+    measured = cache / "physics-measurements.json"
+    commands = [
+        [str(java.with_name("javac")), "-cp", classpath, "-d", str(cache), str(script)],
+        [str(java), "-Xmx1G", "-cp", str(cache) + os.pathsep + classpath, "physics_reference", str(measured)],
+    ]
+    with (cache / "physics-measurements.log").open("w") as log:
+        for command in commands:
+            result = subprocess.run(command, cwd=cache, stdout=log, stderr=subprocess.STDOUT)
+            if result.returncode:
+                raise SystemExit(f"Reference probe failed. Read {cache / 'physics-measurements.log'}")
+    fixture = json.loads(measured.read_text())
+    fixture["provenance"] = {
+        "source_url": f"https://piston-data.mojang.com/v1/objects/{SOURCE_SHA1}/server.jar",
+        "source_sha1": SOURCE_SHA1,
+        "source_sha256": digest(source),
+        "executable_sha256": digest(executable),
+        "probe_sha256": digest(script),
+        "command": "python3 scripts/measure_physics.py --java /path/to/java25/bin/java --output crates/shacraft-physics/tests/fixtures/java26.2.json",
+        "java": subprocess.run([str(java), "-version"], text=True, capture_output=True, check=True).stderr.strip(),
+    }
+    args.output.parent.mkdir(parents=True, exist_ok=True)
+    args.output.write_text(json.dumps(fixture, indent=2) + "\n")
+    print(f"Wrote {args.output}")
+
+
+if __name__ == "__main__":
+    main()