chore: start transition layout — python into version-python/, scaffold version-rust/

- git mv of all existing files into version-python/ (history preserved)
- version-rust/: minimal cargo scaffold (edition 2024), no deps yet
- root AGENTS.md documents the transition rules and artifact/schema contract
- main is untouched; the python layout there stays as-is

version-python/tests/test_extract.py

@@ -0,0 +1,68 @@
+#!/usr/bin/env python3
+"""Offline extraction test with a synthetic export.json (no network, no deps).
+
+Run with: python3 tests/test_extract.py
+"""
+
+from __future__ import annotations
+
+import base64
+import json
+import sys
+import tempfile
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+
+from dlphelper.discord import classify, extract_urls  # noqa: E402
+
+
+def b64(s: str) -> str:
+    return base64.b64encode(s.encode()).decode()
+
+
+def main() -> None:
+    messages = [
+        {
+            "id": "1",
+            "timestamp": "2026-01-01T00:00:00",
+            "author": {"name": "poster"},
+            "content": f"chaos stuff: {b64('https://gofile.io/d/abc123')}",
+        },
+        {
+            "id": "2",
+            "timestamp": "2026-01-02T00:00:00",
+            "author": {"name": "poster"},
+            "content": (
+                f"0807 zip: {b64('https://0807.st/6saCNie.zip')}\n"
+                f"dupe of 1: {b64('https://gofile.io/d/abc123')}\n"
+                f"plain: https://0807.st/plainLink.zip and "
+                f"https://discord.com/channels/1/2 (unsupported)\n"
+                f"junk: {b64('https://pixeldrain.com/u/xyz')} "
+                "and not-our-domain base64: aHR0cHM6Ly9leGFtcGxlLm9yZw=="
+            ),
+        },
+    ]
+
+    with tempfile.TemporaryDirectory() as tmp:
+        export = Path(tmp) / "export.json"
+        export.write_text(json.dumps({"messages": messages}), encoding="utf-8")
+        found = extract_urls(export)
+
+    urls = {f.url for f in found}
+    expected = {"https://gofile.io/d/abc123", "https://0807.st/6saCNie.zip",
+                "https://0807.st/plainLink.zip"}
+    assert urls == expected, f"unexpected urls: {sorted(urls)}"
+
+    by_url = {f.url: f for f in found}
+    g = by_url["https://gofile.io/d/abc123"]
+    assert g.host == "gofile" and g.message_id == "1" and g.author == "poster"
+    assert classify("https://0807.st/x.zip") == "0807"
+    assert classify("https://gofile.io/d/x") == "gofile"
+    assert classify("https://example.org/x") is None
+
+    print("test_extract: OK")
+
+
+if __name__ == "__main__":
+    main()