diff --git a/agent/compaction/equality.go b/agent/compaction/equality.go
index f62a21c1..d56996f9 100644
--- a/agent/compaction/equality.go
+++ b/agent/compaction/equality.go
@@ -70,7 +70,29 @@ func contentEqual(left, right message.Content) bool {
 	case *message.HostedFileContent:
 		rightContent := right.(*message.HostedFileContent)
 		return leftContent.FileID == rightContent.FileID && leftContent.MediaType == rightContent.MediaType && leftContent.Name == rightContent.Name
+	case *message.MCPServerToolCallContent:
+		rightContent := right.(*message.MCPServerToolCallContent)
+		return leftContent.CallID == rightContent.CallID && leftContent.Name == rightContent.Name &&
+			leftContent.ServerName == rightContent.ServerName && leftContent.Arguments == rightContent.Arguments
+	case *message.MCPServerToolResultContent:
+		rightContent := right.(*message.MCPServerToolResultContent)
+		return leftContent.CallID == rightContent.CallID && leftContent.Name == rightContent.Name &&
+			leftContent.ServerName == rightContent.ServerName && leftContent.Error == rightContent.Error &&
+			contentsEqual(leftContent.Outputs, rightContent.Outputs)
+	case *message.CodeInterpreterToolCallContent:
+		rightContent := right.(*message.CodeInterpreterToolCallContent)
+		return leftContent.CallID == rightContent.CallID && contentsEqual(leftContent.Inputs, rightContent.Inputs)
+	case *message.CodeInterpreterToolResultContent:
+		rightContent := right.(*message.CodeInterpreterToolResultContent)
+		return leftContent.CallID == rightContent.CallID && contentsEqual(leftContent.Outputs, rightContent.Outputs)
+	case *message.UsageContent:
+		rightContent := right.(*message.UsageContent)
+		return reflect.DeepEqual(leftContent.Details, rightContent.Details)
 	default:
+		// An unhandled content type is treated as equal so a genuinely new,
+		// forward-compatible content type does not force an index rebuild. The
+		// hosted content types the framework produces are handled explicitly
+		// above so real changes in them are detected.
 		return true
 	}
 }
diff --git a/agent/compaction/equality_test.go b/agent/compaction/equality_test.go
index 346edaf5..95f7797f 100644
--- a/agent/compaction/equality_test.go
+++ b/agent/compaction/equality_test.go
@@ -68,6 +68,12 @@ func TestMessageIndexUpdate_MatchesKnownContentTypes(t *testing.T) {
 		{name: "function result", original: &message.FunctionResultContent{CallID: "c1", Result: "sunny"}, replacement: &message.FunctionResultContent{CallID: "c1", Result: "rainy"}, matches: false},
 		{name: "function result error", original: &message.FunctionResultContent{CallID: "c1", Result: "sunny"}, replacement: &message.FunctionResultContent{CallID: "c1", Result: "sunny", Error: errors.New("boom")}, matches: false},
 		{name: "hosted file", original: &message.HostedFileContent{FileID: "file-1", MediaType: "text/csv", Name: "a.csv"}, replacement: &message.HostedFileContent{FileID: "file-1", MediaType: "text/csv", Name: "a.csv"}, matches: true},
+		{name: "mcp call same", original: &message.MCPServerToolCallContent{CallID: "c1", Name: "fn", Arguments: `{"x":1}`}, replacement: &message.MCPServerToolCallContent{CallID: "c1", Name: "fn", Arguments: `{"x":1}`}, matches: true},
+		{name: "mcp call args differ", original: &message.MCPServerToolCallContent{CallID: "c1", Name: "fn", Arguments: `{"x":1}`}, replacement: &message.MCPServerToolCallContent{CallID: "c1", Name: "fn", Arguments: `{"x":2}`}, matches: false},
+		{name: "mcp result outputs differ", original: &message.MCPServerToolResultContent{CallID: "c1", Outputs: message.Contents{&message.TextContent{Text: "a"}}}, replacement: &message.MCPServerToolResultContent{CallID: "c1", Outputs: message.Contents{&message.TextContent{Text: "b"}}}, matches: false},
+		{name: "code interpreter call inputs differ", original: &message.CodeInterpreterToolCallContent{CallID: "c1", Inputs: message.Contents{&message.TextContent{Text: "x=1"}}}, replacement: &message.CodeInterpreterToolCallContent{CallID: "c1", Inputs: message.Contents{&message.TextContent{Text: "x=2"}}}, matches: false},
+		{name: "code interpreter result outputs differ", original: &message.CodeInterpreterToolResultContent{CallID: "c1", Outputs: message.Contents{&message.TextContent{Text: "1"}}}, replacement: &message.CodeInterpreterToolResultContent{CallID: "c1", Outputs: message.Contents{&message.TextContent{Text: "2"}}}, matches: false},
+		{name: "usage differs", original: &message.UsageContent{Details: message.UsageDetails{InputTokenCount: 10}}, replacement: &message.UsageContent{Details: message.UsageDetails{InputTokenCount: 20}}, matches: false},
 	}
 
 	for _, tt := range tests {