refactor: address CodeRabbit nitpick suggestions

- Update Opus max_output_tokens to 64K (Opus 4.5 spec)
- Replace empty interfaces with Record<string, never> type aliases
- Optimize buildPromptString to iterate in reverse for efficiency
- Make claudeAgentSdk delegate to createClaudeAgentSdk to reduce duplication

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: johann-taberlet

packages/typescript/ai-claude-agent-sdk/src/claude-agent-sdk-adapter.ts

@@ -587,28 +587,20 @@ export class ClaudeAgentSdk extends BaseAdapter<
    * Extracts text content from the last user message.
    */
   private buildPromptString(messages: Array<ModelMessage>): string {
-    // Find all user messages and combine them
-    const userMessages: Array<string> = []
-
-    for (const message of messages) {
-      if (message.role === 'user') {
-        let content: string
+    // Find the last user message by iterating in reverse
+    for (let i = messages.length - 1; i >= 0; i--) {
+      const message = messages[i]
+      if (message?.role === 'user') {
         if (typeof message.content === 'string') {
-          content = message.content
-        } else if (message.content) {
-          content = message.content
+          return message.content
+        } else if (message.content && message.content.length > 0) {
+          return message.content
             .map((part) => this.convertContentPartToText(part))
             .join('\n')
-        } else {
-          content = ''
         }
-        userMessages.push(content)
       }
     }
-
-    // Return the last user message or empty string
-    const lastMessage = userMessages[userMessages.length - 1]
-    return lastMessage ?? ''
+    return ''
   }
 
 }
@@ -660,7 +652,7 @@ export function createClaudeAgentSdk(
  * ```
  */
 export function claudeAgentSdk(config?: ClaudeAgentSdkConfig): ClaudeAgentSdk {
-  return new ClaudeAgentSdk(config)
+  return createClaudeAgentSdk(config)
 }
 
 export type { ClaudeAgentSdkConfig }

packages/typescript/ai-claude-agent-sdk/src/message-types.ts

@@ -72,17 +72,13 @@ export interface ClaudeAgentSdkDocumentMetadata {
  * Metadata for Claude Agent SDK audio content parts.
  * Note: Audio is NOT supported by Claude - placeholder for type compatibility.
  */
-export interface ClaudeAgentSdkAudioMetadata {
-  // Audio not supported - placeholder for type compatibility
-}
+export type ClaudeAgentSdkAudioMetadata = Record<string, never>
 
 /**
  * Metadata for Claude Agent SDK video content parts.
  * Note: Video is NOT supported by Claude - placeholder for type compatibility.
  */
-export interface ClaudeAgentSdkVideoMetadata {
-  // Video not supported - placeholder for type compatibility
-}
+export type ClaudeAgentSdkVideoMetadata = Record<string, never>
 
 /**
  * Map of modality types to their Claude Agent SDK-specific metadata types.

packages/typescript/ai-claude-agent-sdk/src/model-meta.ts

@@ -65,7 +65,7 @@ const CLAUDE_OPUS = {
   name: 'Claude Opus',
   id: 'opus',
   context_window: 200_000,
-  max_output_tokens: 32_000,
+  max_output_tokens: 64_000, // Opus 4.5 supports 64K output tokens
   knowledge_cutoff: '2025-01',
   pricing: {
     input: { normal: 15 },