fix: Use str() to calculate fingerprint instead of json.dumps

This is to avoid serialization issue for some fields that are not json serializable.
meanwhile restructure the debug logs in context cache manager for better debugging potential issues.

PiperOrigin-RevId: 811182492

src/google/adk/models/gemini_context_cache_manager.py

@@ -68,8 +68,19 @@ class GeminiContextCacheManager:
     """
     # Check if we have existing cache metadata and if it's valid
     if llm_request.cache_metadata:
+      logger.debug(
+          "Found existing cache metadata: cache_name=%s, invocations_used=%d,"
+          " cached_contents_count=%d",
+          llm_request.cache_metadata.cache_name,
+          llm_request.cache_metadata.invocations_used,
+          llm_request.cache_metadata.cached_contents_count,
+      )
       if await self._is_cache_valid(llm_request):
         # Valid cache found - use it
+        logger.debug(
+            "Cache is valid, reusing cache: %s",
+            llm_request.cache_metadata.cache_name,
+        )
         cache_name = llm_request.cache_metadata.cache_name
         cache_contents_count = llm_request.cache_metadata.cached_contents_count
         self._apply_cache_to_request(
@@ -78,6 +89,10 @@ class GeminiContextCacheManager:
         return llm_request.cache_metadata.model_copy()
       else:
         # Invalid cache - clean it up
+        logger.debug(
+            "Cache is invalid, cleaning up: %s",
+            llm_request.cache_metadata.cache_name,
+        )
         await self.cleanup_cache(llm_request.cache_metadata.cache_name)
         llm_request.cache_metadata = None
 
@@ -85,6 +100,11 @@ class GeminiContextCacheManager:
     cache_contents_count = self._find_count_of_contents_to_cache(
         llm_request.contents
     )
+    logger.debug(
+        "Determined to cache %d contents from %d total contents",
+        cache_contents_count,
+        len(llm_request.contents),
+    )
 
     # Create new cache with the determined contents
     cache_metadata = await self._create_new_cache_with_contents(
@@ -97,6 +117,9 @@ class GeminiContextCacheManager:
     self._apply_cache_to_request(
         llm_request, cache_metadata.cache_name, cache_contents_count
     )
+    logger.debug(
+        "Successfully applied cache to request: %s", cache_metadata.cache_name
+    )
 
     return cache_metadata
 
@@ -218,8 +241,8 @@ class GeminiContextCacheManager:
         contents_data.append(content.model_dump())
       fingerprint_data["cached_contents"] = contents_data
 
-    # Generate hash
-    fingerprint_str = json.dumps(fingerprint_data, sort_keys=True)
+    # Generate hash using str() instead of json.dumps() to handle bytes
+    fingerprint_str = str(fingerprint_data)
     return hashlib.sha256(fingerprint_str.encode()).hexdigest()[:16]
 
   async def _create_new_cache_with_contents(
@@ -310,6 +333,10 @@ class GeminiContextCacheManager:
     # Add system instruction if present
     if llm_request.config and llm_request.config.system_instruction:
       cache_config.system_instruction = llm_request.config.system_instruction
+      logger.debug(
+          "Added system instruction to cache config (length=%d)",
+          len(llm_request.config.system_instruction),
+      )
 
     # Add tools if present
     if llm_request.config and llm_request.config.tools:
@@ -319,29 +346,30 @@ class GeminiContextCacheManager:
     if llm_request.config and llm_request.config.tool_config:
       cache_config.tool_config = llm_request.config.tool_config
 
-    try:
-      cached_content = await self.genai_client.aio.caches.create(
-          model=llm_request.model,
-          config=cache_config,
-      )
-      # Set precise creation timestamp right after cache creation
-      created_at = time.time()
-      logger.info("Cache created successfully: %s", cached_content.name)
+    logger.debug(
+        "Creating cache with model %s and config: %s",
+        llm_request.model,
+        cache_config,
+    )
+    cached_content = await self.genai_client.aio.caches.create(
+        model=llm_request.model,
+        config=cache_config,
+    )
+    # Set precise creation timestamp right after cache creation
+    created_at = time.time()
+    logger.info("Cache created successfully: %s", cached_content.name)
 
-      # Return complete cache metadata with precise timing
-      return CacheMetadata(
-          cache_name=cached_content.name,
-          expire_time=created_at + llm_request.cache_config.ttl_seconds,
-          fingerprint=self._generate_cache_fingerprint(
-              llm_request, cache_contents_count
-          ),
-          invocations_used=1,
-          cached_contents_count=cache_contents_count,
-          created_at=created_at,
-      )
-    except Exception as e:
-      logger.error("Failed to create Gemini cache: %s", e)
-      raise
+    # Return complete cache metadata with precise timing
+    return CacheMetadata(
+        cache_name=cached_content.name,
+        expire_time=created_at + llm_request.cache_config.ttl_seconds,
+        fingerprint=self._generate_cache_fingerprint(
+            llm_request, cache_contents_count
+        ),
+        invocations_used=1,
+        cached_contents_count=cache_contents_count,
+        created_at=created_at,
+    )
 
   async def cleanup_cache(self, cache_name: str) -> None:
     """Clean up cache by deleting it.
@@ -349,6 +377,7 @@ class GeminiContextCacheManager:
     Args:
         cache_name: Name of cache to delete
     """
+    logger.debug("Attempting to delete cache: %s", cache_name)
     try:
       await self.genai_client.aio.caches.delete(name=cache_name)
       logger.info("Cache cleaned up: %s", cache_name)