initial cost tracking

Signed-off-by: Eason Goodale <easong@openai.com>

codex-cli/tests/context-percent.test.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it } from "vitest";
+
+import type { ResponseItem } from "openai/resources/responses/responses.mjs";
+
+import { calculateContextPercentRemaining } from "../src/components/chat/terminal-chat-utils.js";
+
+function makeUserMessage(id: string, text: string): ResponseItem {
+  return {
+    id,
+    type: "message",
+    role: "user",
+    content: [{ type: "input_text", text }],
+  } as ResponseItem;
+}
+
+describe("calculateContextPercentRemaining", () => {
+  it("includes extra context characters in calculation", () => {
+    const msgText = "a".repeat(40); // 40 chars → 10 tokens
+    const items = [makeUserMessage("1", msgText)];
+
+    const model = "gpt-4-16k";
+
+    const base = calculateContextPercentRemaining(items, model);
+    const withExtra = calculateContextPercentRemaining(items, model, 8); // +8 chars → +2 tokens
+
+    expect(withExtra).toBeLessThan(base);
+  });
+});