feat: add GitHub Copilot provider

Copilot device login + onboarding option; model list auth detection.

src/cli/models-cli.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, it, vi } from "vitest";
+
+const githubCopilotLoginCommand = vi.fn();
+
+vi.mock("../commands/models.js", async () => {
+  const actual = (await vi.importActual<typeof import("../commands/models.js")>(
+    "../commands/models.js",
+  )) as typeof import("../commands/models.js");
+
+  return {
+    ...actual,
+    githubCopilotLoginCommand,
+  };
+});
+
+describe("models cli", () => {
+  it("registers github-copilot login command", async () => {
+    const { Command } = await import("commander");
+    const { registerModelsCli } = await import("./models-cli.js");
+
+    const program = new Command();
+    registerModelsCli(program);
+
+    const models = program.commands.find((cmd) => cmd.name() === "models");
+    expect(models).toBeTruthy();
+
+    const auth = models?.commands.find((cmd) => cmd.name() === "auth");
+    expect(auth).toBeTruthy();
+
+    const login = auth?.commands.find(
+      (cmd) => cmd.name() === "login-github-copilot",
+    );
+    expect(login).toBeTruthy();
+
+    await program.parseAsync(
+      ["models", "auth", "login-github-copilot", "--yes"],
+      {
+        from: "user",
+      },
+    );
+
+    expect(githubCopilotLoginCommand).toHaveBeenCalledTimes(1);
+    expect(githubCopilotLoginCommand).toHaveBeenCalledWith(
+      expect.objectContaining({ yes: true }),
+      expect.any(Object),
+    );
+  });
+});

src/cli/models-cli.ts

@@ -1,6 +1,7 @@
 import type { Command } from "commander";
 
 import {
+  githubCopilotLoginCommand,
   modelsAliasesAddCommand,
   modelsAliasesListCommand,
   modelsAliasesRemoveCommand,
@@ -374,6 +375,31 @@ export function registerModelsCli(program: Command) {
       }
     });
 
+  auth
+    .command("login-github-copilot")
+    .description(
+      "Login to GitHub Copilot via GitHub device flow (TTY required)",
+    )
+    .option(
+      "--profile-id <id>",
+      "Auth profile id (default: github-copilot:github)",
+    )
+    .option("--yes", "Overwrite existing profile without prompting", false)
+    .action(async (opts) => {
+      try {
+        await githubCopilotLoginCommand(
+          {
+            profileId: opts.profileId as string | undefined,
+            yes: Boolean(opts.yes),
+          },
+          defaultRuntime,
+        );
+      } catch (err) {
+        defaultRuntime.error(String(err));
+        defaultRuntime.exit(1);
+      }
+    });
+
   const order = auth
     .command("order")
     .description("Manage per-agent auth profile order overrides");