fix: guard decodeURI(Component) against lone-surrogate crash (#667225)

'String contained an illegal UTF-16 sequence' on first Mini App / site
open for users with a truncated emoji in their Telegram name.

The existing surrogate guard only patched the ENCODE direction
(encodeURI/encodeURIComponent). But Telegram percent-encodes such names
as CESU-8 (%ED%A0%BD) in tgWebAppData, and decodeURI/decodeURIComponent
throw on those bytes in every engine (JSC wording is the reported one) —
any decode of init-data-derived strings crashed into the ErrorBoundary.

Not valibot: valibot 1.0.0 has no UTF-16 well-formedness validation
(verified against the installed package), and upstream pins it exactly,
so there is nothing to bump.

decodeURI/decodeURIComponent now try the native decoder first and fall
back to lenient WHATWG-style UTF-8 decoding with U+FFFD replacement —
the same semantics URLSearchParams applies to the same bytes. Decoded
values still flow through existing validation (getSafeRedirectPath etc),
so nothing becomes less strict.

src/utils/installEncodingSurrogateGuard.ts

@@ -3,24 +3,38 @@ import { sanitizeSurrogates } from './sanitizeSurrogates';
 /**
  * App-wide guard against the "String contained an illegal UTF-16 sequence" crash.
  *
- * A lone (unpaired) UTF-16 surrogate — typically a truncated emoji in a backend
+ * A lone (unpaired) UTF-16 surrogate — typically a truncated emoji in a Telegram
- * name/remark that ends up in a subscription/connection URL — makes encodeURI /
+ * user name or a backend name/remark — crashes the URI functions on both engines
- * encodeURIComponent throw a URIError on iOS WebKit/JavaScriptCore (V8: "URI
+ * (V8: "URI malformed"; iOS WebKit/JavaScriptCore: "String contained an illegal
- * malformed"; Safari/JSC: "String contained an illegal UTF-16 sequence"). Any
+ * UTF-16 sequence"), in BOTH directions:
- * code path that encodes such a string crashes — including third-party libs we
+ *
- * can't edit (e.g. qrcode.react calls encodeURI internally) and any encode call
+ * - encodeURI / encodeURIComponent throw when the INPUT STRING contains a lone
- * added later. The base64 idiom btoa(unescape(encodeURIComponent(x))) is covered
+ *   surrogate (truncated emoji in a subscription URL's remark, a user name fed
+ *   into a link, qrcode.react's internal encodeURI, …).
+ * - decodeURI / decodeURIComponent throw when the INPUT BYTES percent-encode a
+ *   lone surrogate (CESU-8 style %ED%A0%BD). Telegram itself produces such
+ *   sequences in tgWebAppData when the user's name contains a truncated emoji,
+ *   so any decode of init-data-derived strings — ours, @telegram-apps/sdk's, or
+ *   a router's — crashes the Mini App on first open.
+ *
+ * The base64 idiom btoa(unescape(encodeURIComponent(x))) is covered
  * transitively, since its encodeURIComponent is guarded here. (We do NOT patch
  * btoa itself: it rejects every char > U+00FF — Cyrillic, emoji, even the U+FFFD
  * replacement — with a separate "Invalid character" error that sanitising
  * surrogates cannot fix, and nothing base64-encodes raw Unicode directly.)
  *
  * Instead of wrapping every (current and future) call site, we sanitise at the
- * single chokepoint: the global encoders themselves. This is fail-safe, not
+ * single chokepoint: the global codecs themselves. This is fail-safe, not
- * fail-broken — for any well-formed string there are no lone surrogates, so the
+ * fail-broken:
- * output is byte-for-byte identical; only strings that would otherwise have
+ * - encoders: for any well-formed string the output is byte-for-byte identical;
- * thrown get their lone surrogates replaced with U+FFFD (the same remedy as
+ *   only strings that would otherwise have thrown get their lone surrogates
- * String.prototype.toWellFormed()).
+ *   replaced with U+FFFD (the same remedy as String.prototype.toWellFormed()).
+ * - decoders: the native decoder runs first and its result is returned
+ *   unchanged; only when it THROWS do we fall back to lenient WHATWG-style
+ *   UTF-8 decoding with U+FFFD replacement — the exact semantics
+ *   URLSearchParams already applies to the same bytes. Validation that
+ *   inspects the decoded value (e.g. getSafeRedirectPath) still runs on the
+ *   fallback result, so nothing gets less strict.
  *
  * Must run before any rendering or network call. Idempotent.
  */
@@ -32,8 +46,62 @@ export function installEncodingSurrogateGuard(): void {
 
   const nativeEncodeURI = globalThis.encodeURI;
   const nativeEncodeURIComponent = globalThis.encodeURIComponent;
+  const nativeDecodeURI = globalThis.decodeURI;
+  const nativeDecodeURIComponent = globalThis.decodeURIComponent;
 
   globalThis.encodeURI = (uri: string): string => nativeEncodeURI(sanitizeSurrogates(String(uri)));
   globalThis.encodeURIComponent = (uriComponent: string | number | boolean): string =>
     nativeEncodeURIComponent(sanitizeSurrogates(String(uriComponent)));
+  globalThis.decodeURI = (encodedURI: string): string => {
+    const input = String(encodedURI);
+    try {
+      return nativeDecodeURI(input);
+    } catch {
+      return decodePercentSequencesLeniently(input);
+    }
+  };
+  globalThis.decodeURIComponent = (encodedURIComponent: string): string => {
+    const input = String(encodedURIComponent);
+    try {
+      return nativeDecodeURIComponent(input);
+    } catch {
+      return decodePercentSequencesLeniently(input);
+    }
+  };
+}
+
+const HEX_PAIR = /^[0-9a-fA-F]{2}$/;
+
+/**
+ * WHATWG-style lenient percent-decoding: collect %XX bytes (malformed escapes
+ * stay literal) and decode them as UTF-8 with U+FFFD replacement — the same
+ * semantics URLSearchParams applies. Used ONLY after the native decoder threw,
+ * so a replacement glyph in place of a broken emoji half beats taking the
+ * whole app down. Unlike decodeURI, the fallback also decodes reserved
+ * characters — acceptable, since the native result for that input was a crash.
+ */
+function decodePercentSequencesLeniently(input: string): string {
+  const bytes: number[] = [];
+  const encoder = new TextEncoder();
+  let i = 0;
+  while (i < input.length) {
+    if (input[i] === '%' && HEX_PAIR.test(input.slice(i + 1, i + 3))) {
+      bytes.push(parseInt(input.slice(i + 1, i + 3), 16));
+      i += 3;
+      continue;
+    }
+    // Consume the run of literal characters up to the next valid %XX escape.
+    let end = i;
+    while (
+      end < input.length &&
+      !(input[end] === '%' && HEX_PAIR.test(input.slice(end + 1, end + 3)))
+    ) {
+      end += 1;
+    }
+    for (const byte of encoder.encode(input.slice(i, end))) {
+      bytes.push(byte);
+    }
+    i = end;
+  }
+  return new TextDecoder('utf-8', { fatal: false }).decode(new Uint8Array(bytes));
 }