fix(cli): ensure /clear resets context and exclude system messages from approximateTokenUsed count (#443)

https://github.com/user-attachments/assets/58b8f261-a359-4cd8-8c84-90d8d91a5592

codex-cli/src/utils/approximate-tokens-used.ts

@@ -19,6 +19,10 @@ export function approximateTokensUsed(items: Array<ResponseItem>): number {
   for (const item of items) {
     switch (item.type) {
       case "message": {
+        if (item.role !== "user" && item.role !== "assistant") {
+          continue;
+        }
+
         for (const c of item.content) {
           if (c.type === "input_text" || c.type === "output_text") {
             charCount += c.text.length;