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

open-sse/translator/formats/claude.js

@@ -4,6 +4,7 @@ import { ROLE, CLAUDE_BLOCK } from "../schema/index.js";
 import { adjustMaxTokens } from "./maxTokens.js";
 import { applyCloaking } from "../../utils/claudeCloaking.js";
 import { resolveSessionId } from "../../utils/sessionManager.js";
+import { isValidClaudeSignature } from "../../utils/claudeSignature.js";
 import { PROVIDERS } from "../../providers/index.js";
 import { getCapabilitiesForModel } from "../../providers/capabilities.js";
 import { DEFAULT_MAX_TOKENS } from "../../config/runtimeConfig.js";
@@ -213,14 +214,26 @@ export function prepareClaudeRequest(body, provider = null, apiKey = null, conne
           let hasToolUse = false;
           let hasThinking = false;
 
-          // Always replace signature for all thinking blocks
+          // Claude native: preserve valid signatures, drop invalid blocks.
+          // anthropic-compatible: replace with default (safe fallback for lenient upstreams).
+          const isClaudeNative = provider === "claude";
+          const kept = [];
           for (const block of msg.content) {
-            if (block.type === CLAUDE_BLOCK.THINKING || block.type === CLAUDE_BLOCK.REDACTED_THINKING) {
-              block.signature = DEFAULT_THINKING_CLAUDE_SIGNATURE;
+            const isThinking = block.type === CLAUDE_BLOCK.THINKING || block.type === CLAUDE_BLOCK.REDACTED_THINKING;
+            if (isThinking) {
               hasThinking = true;
+              if (isClaudeNative) {
+                if (isValidClaudeSignature(block.signature)) kept.push(block);
+              } else {
+                block.signature = DEFAULT_THINKING_CLAUDE_SIGNATURE;
+                kept.push(block);
+              }
+              continue;
             }
             if (block.type === CLAUDE_BLOCK.TOOL_USE) hasToolUse = true;
+            kept.push(block);
           }
+          msg.content = kept;
 
           // Add thinking block if thinking enabled + has tool_use but no thinking
           if (thinkingEnabled && !hasThinking && hasToolUse) {

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;
+  }
+}