fix: make TruncateHistory pair-aware to prevent orphaned tool messages

When the cut point falls inside a tool_use/tool_result group, snap
backward to include the full group.

pkg/session/manager.go

@@ -141,7 +141,17 @@ func (sm *SessionManager) TruncateHistory(key string, keepLast int) {
 		return
 	}
 
-	session.Messages = session.Messages[len(session.Messages)-keepLast:]
+	// Start with the naive cut point
+	cutIdx := len(session.Messages) - keepLast
+
+	// Snap the cut point backward: if the message at cutIdx is a "tool"
+	// (tool_result), walk backward to include the preceding assistant
+	// message that owns the tool_call group.
+	for cutIdx > 0 && session.Messages[cutIdx].Role == "tool" {
+		cutIdx--
+	}
+
+	session.Messages = session.Messages[cutIdx:]
 	session.Updated = time.Now()
 }
 

pkg/session/manager_test.go

@@ -4,6 +4,8 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+
+	"github.com/sipeed/picoclaw/pkg/providers"
 )
 
 func TestSanitizeFilename(t *testing.T) {
@@ -72,3 +74,54 @@ func TestSave_RejectsPathTraversal(t *testing.T) {
 		}
 	}
 }
+
+func TestTruncateHistory_PreservesToolPairs(t *testing.T) {
+	tmpDir := t.TempDir()
+	sm := NewSessionManager(tmpDir)
+
+	key := "test-truncate"
+	sm.GetOrCreate(key)
+
+	// Build: user, assistant+2tools, tool1, tool2, user, assistant = 6 messages
+	sm.AddFullMessage(key, providers.Message{Role: "user", Content: "q1"})
+	sm.AddFullMessage(key, providers.Message{
+		Role:    "assistant",
+		Content: "checking",
+		ToolCalls: []providers.ToolCall{
+			{ID: "c1", Name: "exec"},
+			{ID: "c2", Name: "web"},
+		},
+	})
+	sm.AddFullMessage(key, providers.Message{Role: "tool", Content: "r1", ToolCallID: "c1"})
+	sm.AddFullMessage(key, providers.Message{Role: "tool", Content: "r2", ToolCallID: "c2"})
+	sm.AddFullMessage(key, providers.Message{Role: "user", Content: "q2"})
+	sm.AddFullMessage(key, providers.Message{Role: "assistant", Content: "done"})
+
+	// keepLast=4 naively keeps: [tool2, user, assistant_done] or similar
+	// which orphans tool messages. Should snap to include/exclude full group.
+	sm.TruncateHistory(key, 4)
+	history := sm.GetHistory(key)
+
+	// Verify no orphaned tool messages
+	toolCallIDs := map[string]bool{}
+	toolResultIDs := map[string]bool{}
+	for _, m := range history {
+		for _, tc := range m.ToolCalls {
+			toolCallIDs[tc.ID] = true
+		}
+		if m.Role == "tool" && m.ToolCallID != "" {
+			toolResultIDs[m.ToolCallID] = true
+		}
+	}
+
+	for id := range toolResultIDs {
+		if !toolCallIDs[id] {
+			t.Errorf("orphaned tool_result %q after truncation", id)
+		}
+	}
+	for id := range toolCallIDs {
+		if !toolResultIDs[id] {
+			t.Errorf("orphaned tool_call %q after truncation", id)
+		}
+	}
+}