Implement Monlet MVP stack and UI updates

server/monlet_server/cursors.py

@@ -0,0 +1,29 @@
+import base64
+import binascii
+from datetime import datetime
+
+from fastapi import HTTPException
+
+
+def encode(*parts: object) -> str:
+    raw = "|".join(str(p) for p in parts).encode()
+    return base64.urlsafe_b64encode(raw).decode().rstrip("=")
+
+
+def decode(cursor: str, count: int) -> list[str]:
+    pad = "=" * (-len(cursor) % 4)
+    try:
+        raw = base64.urlsafe_b64decode(cursor + pad).decode()
+    except (binascii.Error, ValueError) as exc:
+        raise HTTPException(status_code=400, detail="invalid cursor") from exc
+    parts = raw.split("|", count - 1)
+    if len(parts) != count:
+        raise HTTPException(status_code=400, detail="invalid cursor")
+    return parts
+
+
+def decode_datetime(value: str) -> datetime:
+    try:
+        return datetime.fromisoformat(value)
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail="invalid cursor") from exc