Cobblemon Survival Pack: phases 0-2 and Phase 3 zones and hazards

Free NeoForge 1.21.1 modpack on Cobblemon 1.8.4 built with packwiz, plus
the Kotlin companion mod (cobblesurvival) and its built-in data pack.

- Phase 0: packwiz pack with Modrinth/CurseForge cross-links, build and
  export tooling, Prism instance sync, test server with smoke checks.
- Phase 1: Poke Ball shaped island (WorldGen Editor preset, seed isle-26),
  Adrian's biome list, no natural ore, structures without ore or vanilla
  mobs, no Nether portals, world template builder and world report.
- Phase 2: permadeath (CobbleHardcoreMon plus the companion mod's gap
  fixes), Revival Charm, expensive Healing Machine, Lootr refreshing
  loot, in-game self-tests on Minecraft's GameTest framework.
- Phase 3 so far: 14 zones with their own spawn pools and level bands
  (tools/zone_layout.py, tools/zone_spawns.py, "zone" spawn condition),
  Cold Sweat heat and cold as gates with boss-drop insulation recipes,
  spawn survey and hazard self-tests in tools/quick_check.py.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/fieldguide/nbt.py

@@ -0,0 +1,65 @@
+"""Minimal reader for gzipped NBT structure templates (data/*/structure/*.nbt).
+
+Only what the field guide needs: the palette, block-entity strings (loot
+tables, jigsaw pools) and entity ids. Returns plain Python values.
+"""
+import gzip
+import io
+import struct
+
+
+def _read(f, tag):
+    if tag == 1:
+        return struct.unpack(">b", f.read(1))[0]
+    if tag == 2:
+        return struct.unpack(">h", f.read(2))[0]
+    if tag == 3:
+        return struct.unpack(">i", f.read(4))[0]
+    if tag == 4:
+        return struct.unpack(">q", f.read(8))[0]
+    if tag == 5:
+        return struct.unpack(">f", f.read(4))[0]
+    if tag == 6:
+        return struct.unpack(">d", f.read(8))[0]
+    if tag == 7:
+        return f.read(struct.unpack(">i", f.read(4))[0])
+    if tag == 8:
+        return f.read(struct.unpack(">H", f.read(2))[0]).decode("utf-8", "replace")
+    if tag == 9:
+        inner, n = struct.unpack(">bi", f.read(5))
+        return [_read(f, inner) for _ in range(n)]
+    if tag == 10:
+        out = {}
+        while True:
+            t = f.read(1)[0]
+            if t == 0:
+                return out
+            name = f.read(struct.unpack(">H", f.read(2))[0]).decode("utf-8", "replace")
+            out[name] = _read(f, t)
+    if tag == 11:
+        n = struct.unpack(">i", f.read(4))[0]
+        return list(struct.unpack(f">{n}i", f.read(4 * n)))
+    if tag == 12:
+        n = struct.unpack(">i", f.read(4))[0]
+        return list(struct.unpack(f">{n}q", f.read(8 * n)))
+    raise ValueError(f"bad NBT tag {tag}")
+
+
+def load(raw):
+    data = gzip.decompress(raw) if raw[:2] == b"\x1f\x8b" else raw
+    f = io.BytesIO(data)
+    tag = f.read(1)[0]
+    f.read(struct.unpack(">H", f.read(2))[0])
+    return _read(f, tag)
+
+
+def strings(value):
+    """Every string inside a decoded NBT value."""
+    if isinstance(value, str):
+        yield value
+    elif isinstance(value, dict):
+        for v in value.values():
+            yield from strings(v)
+    elif isinstance(value, list):
+        for v in value:
+            yield from strings(v)