feat: user config api key (#569)

Adds support for reading OPENAI_API_KEY (and other variables) from a
user‑wide dotenv file (~/.codex.config). Precedence order is now:
  1. explicit environment variable
  2. project‑local .env (loaded earlier)
  3. ~/.codex.config

Also adds a regression test that ensures the multiline editor correctly
handles cases where printable text and the CSI‑u Shift+Enter sequence
arrive in the same input chunk.

House‑kept with Prettier; removed stray temp.json artifact.

codex-cli/tests/user-config-env.test.ts

@@ -0,0 +1,62 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { mkdtempSync, writeFileSync, rmSync } from "fs";
+import { tmpdir } from "os";
+import { join } from "path";
+
+/**
+ * Verifies that ~/.codex.env is parsed (lowest‑priority) when present.
+ */
+
+describe("user‑wide ~/.codex.env support", () => {
+  const ORIGINAL_HOME = process.env["HOME"];
+  const ORIGINAL_API_KEY = process.env["OPENAI_API_KEY"];
+
+  let tempHome: string;
+
+  beforeEach(() => {
+    // Create an isolated fake $HOME directory.
+    tempHome = mkdtempSync(join(tmpdir(), "codex-home-"));
+    process.env["HOME"] = tempHome;
+
+    // Ensure the env var is unset so that the file value is picked up.
+    delete process.env["OPENAI_API_KEY"];
+
+    // Write ~/.codex.env with a dummy key.
+    writeFileSync(
+      join(tempHome, ".codex.env"),
+      "OPENAI_API_KEY=my-home-key\n",
+      {
+        encoding: "utf8",
+      },
+    );
+  });
+
+  afterEach(() => {
+    // Cleanup temp directory.
+    try {
+      rmSync(tempHome, { recursive: true, force: true });
+    } catch {
+      // ignore
+    }
+
+    // Restore original env.
+    if (ORIGINAL_HOME !== undefined) {
+      process.env["HOME"] = ORIGINAL_HOME;
+    } else {
+      delete process.env["HOME"];
+    }
+
+    if (ORIGINAL_API_KEY !== undefined) {
+      process.env["OPENAI_API_KEY"] = ORIGINAL_API_KEY;
+    } else {
+      delete process.env["OPENAI_API_KEY"];
+    }
+  });
+
+  it("loads the API key from ~/.codex.env when not set elsewhere", async () => {
+    // Import the config module AFTER setting up the fake env.
+    const { getApiKey } = await import("../src/utils/config.js");
+
+    expect(getApiKey("openai")).toBe("my-home-key");
+  });
+});