fix(memory): prevent context memory loss by improving trim strategy

agent/protocol/agent_stream.py

@@ -8,7 +8,7 @@ import time
 from typing import List, Dict, Any, Optional, Callable, Tuple
 
 from agent.protocol.models import LLMRequest, LLMModel
-from agent.protocol.message_utils import sanitize_claude_messages
+from agent.protocol.message_utils import sanitize_claude_messages, compress_turn_to_text_only
 from agent.tools.base_tool import BaseTool, ToolResult
 from common.log import logger
 
@@ -191,6 +191,11 @@ class AgentStreamExecutor:
             ]
         })
 
+        # Trim context ONCE before the agent loop starts, not during tool steps.
+        # This ensures tool_use/tool_result chains created during the current run
+        # are never stripped mid-execution (which would cause LLM loops).
+        self._trim_messages()
+
         self._emit_event("agent_start")
 
         final_response = ""
@@ -481,14 +486,10 @@ class AgentStreamExecutor:
         Returns:
             (response_text, tool_calls)
         """
-        # Validate and fix message history first
-        self._validate_and_fix_messages()
-        
-        # Trim messages if needed (using agent's context management)
-        self._trim_messages()
-
-        # Re-validate after trimming: trimming may produce new orphaned
-        # tool_result messages when it removes turns at the boundary.
+        # Validate and fix message history (e.g. orphaned tool_result blocks).
+        # Context trimming is done once in run_stream() before the loop starts,
+        # NOT here — trimming mid-execution would strip the current run's
+        # tool_use/tool_result chains and cause LLM loops.
         self._validate_and_fix_messages()
 
         # Prepare messages
@@ -1165,10 +1166,10 @@ class AgentStreamExecutor:
         if not turns:
             return
         
-        # Step 2: 轮次限制 - 超出时裁到 max_turns/2，批量 flush 被裁的轮次
+        # Step 2: 轮次限制 - 超出时移除前一半，保留后一半
         if len(turns) > self.max_context_turns:
-            keep_count = max(1, self.max_context_turns // 2)
-            removed_count = len(turns) - keep_count
+            removed_count = len(turns) // 2
+            keep_count = len(turns) - removed_count
             
             # Flush discarded turns to daily memory
             if self.agent.memory_manager:
@@ -1223,9 +1224,47 @@ class AgentStreamExecutor:
                 logger.info(f"   重建消息列表: {old_count} -> {len(self.messages)} 条消息")
             return
 
-        # Token limit exceeded - keep the latest half of turns (same strategy as turn limit)
-        keep_count = max(1, len(turns) // 2)
-        removed_count = len(turns) - keep_count
+        # Token limit exceeded — tiered strategy based on turn count:
+        #
+        #   Few turns (<5):  Compress ALL turns to text-only (strip tool chains,
+        #                    keep user query + final reply).  Never discard turns
+        #                    — losing even one is too painful when context is thin.
+        #
+        #   Many turns (>=5): Directly discard the first half of turns.
+        #                     With enough turns the oldest ones are less
+        #                     critical, and keeping the recent half intact
+        #                     (with full tool chains) is more useful.
+
+        COMPRESS_THRESHOLD = 5
+
+        if len(turns) < COMPRESS_THRESHOLD:
+            # --- Few turns: compress ALL turns to text-only, never discard ---
+            compressed_turns = []
+            for t in turns:
+                compressed = compress_turn_to_text_only(t)
+                if compressed["messages"]:
+                    compressed_turns.append(compressed)
+
+            new_messages = []
+            for turn in compressed_turns:
+                new_messages.extend(turn["messages"])
+
+            new_tokens = sum(self._estimate_turn_tokens(t) for t in compressed_turns)
+            old_count = len(self.messages)
+            self.messages = new_messages
+
+            logger.info(
+                f"📦 上下文tokens超限(轮次<{COMPRESS_THRESHOLD}): "
+                f"~{current_tokens + system_tokens} > {max_tokens}，"
+                f"压缩全部 {len(turns)} 轮为纯文本 "
+                f"({old_count} -> {len(self.messages)} 条消息，"
+                f"~{current_tokens + system_tokens} -> ~{new_tokens + system_tokens} tokens)"
+            )
+            return
+
+        # --- Many turns (>=5): discard the older half, keep the newer half ---
+        removed_count = len(turns) // 2
+        keep_count = len(turns) - removed_count
         kept_turns = turns[-keep_count:]
         kept_tokens = sum(self._estimate_turn_tokens(t) for t in kept_turns)
 
@@ -1234,7 +1273,6 @@ class AgentStreamExecutor:
             f"裁剪至 {keep_count} 轮（移除 {removed_count} 轮）"
         )
 
-        # Flush discarded turns to daily memory
         if self.agent.memory_manager:
             discarded_messages = []
             for turn in turns[:removed_count]:
@@ -1245,14 +1283,14 @@ class AgentStreamExecutor:
                     messages=discarded_messages, user_id=user_id,
                     reason="trim", max_messages=0
                 )
-        
+
         new_messages = []
         for turn in kept_turns:
             new_messages.extend(turn['messages'])
-        
+
         old_count = len(self.messages)
         self.messages = new_messages
-        
+
         logger.info(
             f"   移除了 {removed_count} 轮对话 "
             f"({old_count} -> {len(self.messages)} 条消息，"