diff --git a/cmd/olliesrv/internal/agent/history.go b/cmd/olliesrv/internal/agent/history.go
index 6f0308e..ae7e14d 100644
--- a/cmd/olliesrv/internal/agent/history.go
+++ b/cmd/olliesrv/internal/agent/history.go
@@ -104,7 +104,8 @@ func toolMessageID(m backend.Message) string {
 const coldSummaryCacheVersion = "v2"
 
 func toolSummaryHash(m backend.Message) string {
-	h := sha256.Sum256([]byte(normalizeSummaryCacheContent(m.Content)))
+	input := coldSummaryCacheVersion + "\x00" + m.ToolName + "\x00" + normalizeSummaryCacheContent(m.Content)
+	h := sha256.Sum256([]byte(input))
 	return "cold-summary:" + coldSummaryCacheVersion + ":" + hex.EncodeToString(h[:])
 }
 
@@ -185,6 +186,7 @@ func (s *History) update(assistant backend.Message, results []toolResult) {
 			Content:       r.Content,
 			ContentBlocks: r.ContentBlocks,
 			ToolCallID:    r.ToolCallID,
+			ToolName:      r.Name,
 		}
 		if r.ToolCallID != "" {
 			m.ID = toolMessageID(m)
diff --git a/cmd/olliesrv/internal/agent/summary_cache_test.go b/cmd/olliesrv/internal/agent/summary_cache_test.go
index d7be978..d3873be 100644
--- a/cmd/olliesrv/internal/agent/summary_cache_test.go
+++ b/cmd/olliesrv/internal/agent/summary_cache_test.go
@@ -11,6 +11,14 @@ func messageWithContent(callID, content string) backend.Message {
 	return backend.Message{Role: "tool", ToolCallID: callID, Content: content}
 }
 
+func TestToolSummaryHashSeparatesToolNames(t *testing.T) {
+	first := toolSummaryHash(backend.Message{Role: "tool", ToolName: "shell", Content: "same result"})
+	second := toolSummaryHash(backend.Message{Role: "tool", ToolName: "file_read", Content: "same result"})
+	if first == second {
+		t.Fatal("different tool names produced the same hash")
+	}
+}
+
 func TestNormalizeSummaryCacheContentPlainText(t *testing.T) {
 	got := normalizeSummaryCacheContent(" first line  \r\n\r\n\nsecond line \t\n\n")
 	if got != "first line\n\nsecond line" {
diff --git a/cmd/olliesrv/internal/backend/backend.go b/cmd/olliesrv/internal/backend/backend.go
index 48a70db..b307799 100644
--- a/cmd/olliesrv/internal/backend/backend.go
+++ b/cmd/olliesrv/internal/backend/backend.go
@@ -39,6 +39,7 @@ type Message struct {
 	ContentBlocks  []ContentBlock `json:"content_blocks,omitempty"`  // when set, overrides Content
 	ToolCalls      []ToolCall     `json:"tool_calls,omitempty"`      // set by assistant when calling tools
 	ToolCallID     string         `json:"tool_call_id,omitempty"`    // set on role=tool replies (required by OpenAI)
+	ToolName       string         `json:"tool_name,omitempty"`       // local tool identity for history/cache semantics
 	SummaryApplied bool           `json:"summary_applied,omitempty"` // local history state
 }