Add checkout command with co alias

src/cli.ts

@@ -10,6 +10,7 @@ import { action as openAction } from "./commands/open.ts"
 import { action as reviewAction } from "./commands/review.ts"
 import { action as shellAction } from "./commands/shell.ts"
 import { action as closeAction } from "./commands/close.ts"
+import { action as checkoutAction } from "./commands/checkout.ts"
 import { action as mergeAction } from "./commands/merge.ts"
 import { action as squashAction } from "./commands/squash.ts"
 import { action as rebaseAction } from "./commands/rebase.ts"
@@ -81,6 +82,19 @@ program
   .description("Remove a session (alias for close)")
   .action((branch: string, opts: { force?: boolean }) => closeAction(branch, opts))
 
+program
+  .command("checkout")
+  .argument("<branch>", "branch name")
+  .option("-f, --force", "checkout even if there are unsaved changes")
+  .description("Close the session and check out the branch locally")
+  .action((branch: string, opts: { force?: boolean }) => checkoutAction(branch, opts))
+
+program
+  .command("co", { hidden: true })
+  .argument("<branch>", "branch name")
+  .option("-f, --force", "checkout even if there are unsaved changes")
+  .action((branch: string, opts: { force?: boolean }) => checkoutAction(branch, opts))
+
 // ── Branch ──────────────────────────────────────────────────────────
 
 program.commandsGroup("Branch Commands:")

src/commands/checkout.ts

@@ -0,0 +1,35 @@
+import { join } from "path"
+import { unlink } from "fs/promises"
+import * as git from "../git.ts"
+import * as vm from "../vm.ts"
+import * as state from "../state.ts"
+import { die } from "../fmt.ts"
+
+export async function action(branch: string, opts: { force?: boolean } = {}) {
+  const root = await git.repoRoot()
+  const session = await state.getSession(root, branch)
+
+  if (!session) {
+    die(`No session found for branch "${branch}"`)
+  }
+
+  const worktreeAbs = session.worktree
+
+  if (!opts.force && await git.isDirty(worktreeAbs)) {
+    die(`Branch "${branch}" has unsaved changes. Run "sandlot save ${branch}" first, or use -f to force.`)
+  }
+
+  await vm.clearActivity(worktreeAbs, branch)
+
+  await git.removeWorktree(worktreeAbs, root)
+    .catch((e) => console.warn(`⚠ Failed to remove worktree: ${e.message}`))
+
+  await unlink(join(root, '.sandlot', branch))
+    .catch(() => {}) // symlink may not exist
+
+  await state.removeSession(root, branch)
+
+  await git.checkout(branch, root)
+
+  console.log(`✔ Checked out ${branch}`)
+}