Refactor Terminal and AIAgent cleanup

agent/prompt_caching.py

@@ -0,0 +1,68 @@
+"""Anthropic prompt caching (system_and_3 strategy).
+
+Reduces input token costs by ~75% on multi-turn conversations by caching
+the conversation prefix. Uses 4 cache_control breakpoints (Anthropic max):
+  1. System prompt (stable across all turns)
+  2-4. Last 3 non-system messages (rolling window)
+
+Pure functions -- no class state, no AIAgent dependency.
+"""
+
+import copy
+from typing import Any, Dict, List
+
+
+def _apply_cache_marker(msg: dict, cache_marker: dict) -> None:
+    """Add cache_control to a single message, handling all format variations."""
+    role = msg.get("role", "")
+    content = msg.get("content")
+
+    if role == "tool":
+        msg["cache_control"] = cache_marker
+        return
+
+    if content is None:
+        msg["cache_control"] = cache_marker
+        return
+
+    if isinstance(content, str):
+        msg["content"] = [{"type": "text", "text": content, "cache_control": cache_marker}]
+        return
+
+    if isinstance(content, list) and content:
+        last = content[-1]
+        if isinstance(last, dict):
+            last["cache_control"] = cache_marker
+
+
+def apply_anthropic_cache_control(
+    api_messages: List[Dict[str, Any]],
+    cache_ttl: str = "5m",
+) -> List[Dict[str, Any]]:
+    """Apply system_and_3 caching strategy to messages for Anthropic models.
+
+    Places up to 4 cache_control breakpoints: system prompt + last 3 non-system messages.
+
+    Returns:
+        Deep copy of messages with cache_control breakpoints injected.
+    """
+    messages = copy.deepcopy(api_messages)
+    if not messages:
+        return messages
+
+    marker = {"type": "ephemeral"}
+    if cache_ttl == "1h":
+        marker["ttl"] = "1h"
+
+    breakpoints_used = 0
+
+    if messages[0].get("role") == "system":
+        _apply_cache_marker(messages[0], marker)
+        breakpoints_used += 1
+
+    remaining = 4 - breakpoints_used
+    non_sys = [i for i in range(len(messages)) if messages[i].get("role") != "system"]
+    for idx in non_sys[-remaining:]:
+        _apply_cache_marker(messages[idx], marker)
+
+    return messages