feat(ponytail): introduce "Ponytail" feature for minimalistic code generation

open-sse/utils/claudeSignature.js

@@ -0,0 +1,41 @@
+// Claude thinking signature validation (ported from CLIProxyAPI internal/signature).
+// E-form: single-layer base64, decoded[0] == 0x12 (Claude marker).
+// R-form: double-layer base64, outer decoded[0] == 'E', inner decoded[0] == 0x12.
+// Cache prefix "...#sig" stripped before validation.
+
+const MAX_CLAUDE_SIGNATURE_LEN = 32 * 1024 * 1024;
+const CLAUDE_SIGNATURE_MARKER = 0x12;
+
+function stripCachePrefix(rawSignature) {
+  const sig = (rawSignature || "").trim();
+  if (!sig) return "";
+  const idx = sig.indexOf("#");
+  return idx >= 0 ? sig.slice(idx + 1).trim() : sig;
+}
+
+export function hasClaudeSignaturePrefix(rawSignature) {
+  const sig = stripCachePrefix(rawSignature);
+  return sig.length > 0 && (sig[0] === "E" || sig[0] === "R");
+}
+
+// Strict-ish: validates base64 layers + Claude marker byte.
+export function isValidClaudeSignature(rawSignature) {
+  const sig = stripCachePrefix(rawSignature);
+  if (!sig || sig.length > MAX_CLAUDE_SIGNATURE_LEN) return false;
+
+  try {
+    if (sig[0] === "E") {
+      const decoded = Buffer.from(sig, "base64");
+      return decoded.length > 0 && decoded[0] === CLAUDE_SIGNATURE_MARKER;
+    }
+    if (sig[0] === "R") {
+      const outer = Buffer.from(sig, "base64");
+      if (!outer.length || outer[0] !== 0x45) return false; // 'E'
+      const inner = Buffer.from(outer.toString(), "base64");
+      return inner.length > 0 && inner[0] === CLAUDE_SIGNATURE_MARKER;
+    }
+    return false;
+  } catch {
+    return false;
+  }
+}