feat: add openai model info configuration (#551)

In reference to [Issue 548](https://github.com/openai/codex/issues/548)
- part 1.

codex-cli/tests/model-info.test.ts

@@ -0,0 +1,19 @@
+import { describe, expect, test } from "vitest";
+import { openAiModelInfo } from "../src/utils/model-info";
+
+describe("Model Info", () => {
+  test("supportedModelInfo contains expected models", () => {
+    expect(openAiModelInfo).toHaveProperty("gpt-4o");
+    expect(openAiModelInfo).toHaveProperty("gpt-4.1");
+    expect(openAiModelInfo).toHaveProperty("o3");
+  });
+
+  test("model info entries have required properties", () => {
+    Object.entries(openAiModelInfo).forEach(([_, info]) => {
+      expect(info).toHaveProperty("label");
+      expect(info).toHaveProperty("maxContextLength");
+      expect(typeof info.label).toBe("string");
+      expect(typeof info.maxContextLength).toBe("number");
+    });
+  });
+});

codex-cli/tests/model-utils.test.ts

@@ -0,0 +1,78 @@
+import { describe, test, expect } from "vitest";
+import {
+  calculateContextPercentRemaining,
+  maxTokensForModel,
+} from "../src/utils/model-utils";
+import { openAiModelInfo } from "../src/utils/model-info";
+import type { ResponseItem } from "openai/resources/responses/responses.mjs";
+
+describe("Model Utils", () => {
+  describe("openAiModelInfo", () => {
+    test("model info entries have required properties", () => {
+      Object.entries(openAiModelInfo).forEach(([_, info]) => {
+        expect(info).toHaveProperty("label");
+        expect(info).toHaveProperty("maxContextLength");
+        expect(typeof info.label).toBe("string");
+        expect(typeof info.maxContextLength).toBe("number");
+      });
+    });
+  });
+
+  describe("maxTokensForModel", () => {
+    test("returns correct token limit for known models", () => {
+      const knownModel = "gpt-4o";
+      const expectedTokens = openAiModelInfo[knownModel].maxContextLength;
+      expect(maxTokensForModel(knownModel)).toBe(expectedTokens);
+    });
+
+    test("handles models with size indicators in their names", () => {
+      expect(maxTokensForModel("some-model-32k")).toBe(32000);
+      expect(maxTokensForModel("some-model-16k")).toBe(16000);
+      expect(maxTokensForModel("some-model-8k")).toBe(8000);
+      expect(maxTokensForModel("some-model-4k")).toBe(4000);
+    });
+
+    test("defaults to 128k for unknown models not in the registry", () => {
+      expect(maxTokensForModel("completely-unknown-model")).toBe(128000);
+    });
+  });
+
+  describe("calculateContextPercentRemaining", () => {
+    test("returns 100% for empty items", () => {
+      const result = calculateContextPercentRemaining([], "gpt-4o");
+      expect(result).toBe(100);
+    });
+
+    test("calculates percentage correctly for non-empty items", () => {
+      const mockItems: Array<ResponseItem> = [
+        {
+          id: "test-id",
+          type: "message",
+          role: "user",
+          status: "completed",
+          content: [
+            {
+              type: "input_text",
+              text: "A".repeat(
+                openAiModelInfo["gpt-4o"].maxContextLength * 0.25 * 4,
+              ),
+            },
+          ],
+        } as ResponseItem,
+      ];
+
+      const result = calculateContextPercentRemaining(mockItems, "gpt-4o");
+      expect(result).toBeCloseTo(75, 0);
+    });
+
+    test("handles models that are not in the registry", () => {
+      const mockItems: Array<ResponseItem> = [];
+
+      const result = calculateContextPercentRemaining(
+        mockItems,
+        "unknown-model",
+      );
+      expect(result).toBe(100);
+    });
+  });
+});