Signature handling for fallback

src/format/signature-cache.js

@@ -5,11 +5,15 @@
  * Gemini models require thoughtSignature on tool calls, but Claude Code
  * strips non-standard fields. This cache stores signatures by tool_use_id
  * so they can be restored in subsequent requests.
+ *
+ * Also caches thinking block signatures with model family for cross-model
+ * compatibility checking.
  */
 
-import { GEMINI_SIGNATURE_CACHE_TTL_MS } from '../constants.js';
+import { GEMINI_SIGNATURE_CACHE_TTL_MS, MIN_SIGNATURE_LENGTH } from '../constants.js';
 
 const signatureCache = new Map();
+const thinkingSignatureCache = new Map();
 
 /**
  * Store a signature for a tool_use_id
@@ -54,6 +58,11 @@ export function cleanupCache() {
             signatureCache.delete(key);
         }
     }
+    for (const [key, entry] of thinkingSignatureCache) {
+        if (now - entry.timestamp > GEMINI_SIGNATURE_CACHE_TTL_MS) {
+            thinkingSignatureCache.delete(key);
+        }
+    }
 }
 
 /**
@@ -63,3 +72,43 @@ export function cleanupCache() {
 export function getCacheSize() {
     return signatureCache.size;
 }
+
+/**
+ * Cache a thinking block signature with its model family
+ * @param {string} signature - The thinking signature to cache
+ * @param {string} modelFamily - The model family ('claude' or 'gemini')
+ */
+export function cacheThinkingSignature(signature, modelFamily) {
+    if (!signature || signature.length < MIN_SIGNATURE_LENGTH) return;
+    thinkingSignatureCache.set(signature, {
+        modelFamily,
+        timestamp: Date.now()
+    });
+}
+
+/**
+ * Get the cached model family for a thinking signature
+ * @param {string} signature - The signature to look up
+ * @returns {string|null} 'claude', 'gemini', or null if not found/expired
+ */
+export function getCachedSignatureFamily(signature) {
+    if (!signature) return null;
+    const entry = thinkingSignatureCache.get(signature);
+    if (!entry) return null;
+
+    // Check TTL
+    if (Date.now() - entry.timestamp > GEMINI_SIGNATURE_CACHE_TTL_MS) {
+        thinkingSignatureCache.delete(signature);
+        return null;
+    }
+
+    return entry.modelFamily;
+}
+
+/**
+ * Get the current thinking signature cache size (for debugging)
+ * @returns {number} Number of entries in the thinking signature cache
+ */
+export function getThinkingCacheSize() {
+    return thinkingSignatureCache.size;
+}