feat(anthropic): Align Anthropic integration with latest SDK and enable prompt caching beta

ai_client.py

@@ -18,6 +18,7 @@ import datetime
 from pathlib import Path
 import file_cache
 import mcp_client
+import anthropic
 from google import genai
 from google.genai import types
 from events import EventEmitter
@@ -155,7 +156,7 @@ class ProviderError(Exception):
 
 def _classify_anthropic_error(exc: Exception) -> ProviderError:
     try:
-        import anthropic
+
         if isinstance(exc, anthropic.RateLimitError):
             return ProviderError("rate_limit", "anthropic", exc)
         if isinstance(exc, anthropic.AuthenticationError):
@@ -292,7 +293,7 @@ def _list_gemini_models(api_key: str) -> list[str]:
 
 
 def _list_anthropic_models() -> list[str]:
-    import anthropic
+
     try:
         creds = _load_credentials()
         client = anthropic.Anthropic(api_key=creds["anthropic"]["api_key"])
@@ -858,9 +859,12 @@ def _trim_anthropic_history(system_blocks: list[dict], history: list[dict]):
 def _ensure_anthropic_client():
     global _anthropic_client
     if _anthropic_client is None:
-        import anthropic
         creds = _load_credentials()
-        _anthropic_client = anthropic.Anthropic(api_key=creds["anthropic"]["api_key"])
+        # Enable prompt caching beta
+        _anthropic_client = anthropic.Anthropic(
+            api_key=creds["anthropic"]["api_key"],
+            default_headers={"anthropic-beta": "prompt-caching-2024-07-31"}
+        )
 
 
 def _chunk_text(text: str, chunk_size: int) -> list[str]: