perf: Shorten shared character sheet URLs

Use URL-safe base64 (base64url) for the ?c= payload so it no longer
needs percent-encoding, and prune empty string/array fields before
encoding. Decoding accepts standard base64, so existing links still load.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/CharacterSheet.tsx

@@ -133,22 +133,37 @@ const BLANK_BONDS: Bond[] = Array.from({ length: 6 }, () => ({
   feelings: [],
 }));
 
+// URL-safe base64 (RFC 4648 §5): avoids +, /, = so the result needs no
+// percent-encoding in a query string. Accepts standard base64 on decode too,
+// so links shared before this change still load.
+function bytesToBase64Url(bytes: Uint8Array) {
+  let binary = "";
+  for (let i = 0; i < bytes.length; i++)
+    binary += String.fromCharCode(bytes[i]);
+  return btoa(binary)
+    .replace(/\+/g, "-")
+    .replace(/\//g, "_")
+    .replace(/=+$/, "");
+}
+
+function base64UrlToBytes(b64: string) {
+  let std = b64.replace(/-/g, "+").replace(/_/g, "/");
+  if (std.length % 4) std += "=".repeat(4 - (std.length % 4));
+  return Uint8Array.from(atob(std), (c) => c.charCodeAt(0));
+}
+
 async function compressToBase64(str: string) {
   const stream = new CompressionStream("deflate-raw");
   const writer = stream.writable.getWriter();
   writer.write(new TextEncoder().encode(str));
   writer.close();
   const buf = await new Response(stream.readable).arrayBuffer();
-  const bytes = new Uint8Array(buf);
+  return bytesToBase64Url(new Uint8Array(buf));
-  let binary = "";
-  for (let i = 0; i < bytes.length; i++)
-    binary += String.fromCharCode(bytes[i]);
-  return btoa(binary);
 }
 
 async function decompressFromBase64(b64: string) {
   try {
-    const bytes = Uint8Array.from(atob(b64), (c) => c.charCodeAt(0));
+    const bytes = base64UrlToBytes(b64);
     const stream = new DecompressionStream("deflate-raw");
     const writer = stream.writable.getWriter();
     writer.write(bytes);
@@ -160,6 +175,16 @@ async function decompressFromBase64(b64: string) {
   }
 }
 
+// Drop empty strings and empty arrays before encoding: a sheet is mostly blank
+// text fields, and applyData() restores any missing key to its default.
+function pruneEmpty(data: Record<string, unknown>) {
+  return Object.fromEntries(
+    Object.entries(data).filter(
+      ([, v]) => v !== "" && !(Array.isArray(v) && v.length === 0),
+    ),
+  );
+}
+
 export default function CharacterSheet() {
   const [activeTab, setActiveTab] = useState("main");
   const [urlMode, setUrlMode] = useState(false);
@@ -452,12 +477,11 @@ export default function CharacterSheet() {
   );
 
   const copyShareURL = useCallback(async () => {
-    const encoded = await compressToBase64(JSON.stringify(collectData()));
+    const encoded = await compressToBase64(
+      JSON.stringify(pruneEmpty(collectData())),
+    );
     await navigator.clipboard.writeText(
-      window.location.origin +
+      window.location.origin + window.location.pathname + "?c=" + encoded,
-        window.location.pathname +
-        "?c=" +
-        encodeURIComponent(encoded),
     );
     setCopyStatus(true);
     setTimeout(() => setCopyStatus(false), 2000);