add sandlot shell <branch> command to open a shell in a session's worktree

src/cli.ts

@@ -355,6 +355,24 @@ program
     }
   })
 
+// ── sandlot shell <branch> ───────────────────────────────────────────
+
+program
+  .command("shell")
+  .argument("<branch>", "branch name")
+  .description("Open a shell in the VM at the session's worktree")
+  .action(async (branch: string) => {
+    const root = await git.repoRoot()
+    const session = await state.getSession(root, branch)
+    if (!session) {
+      console.error(`✖ No session found for branch "${branch}".`)
+      process.exit(1)
+    }
+
+    await vm.ensure()
+    await vm.shell(session.worktree)
+  })
+
 // ── sandlot close <branch> ───────────────────────────────────────────
 
 const closeAction = async (branch: string) => {

src/vm.ts

@@ -202,12 +202,12 @@ export async function claude(workdir: string, opts?: { prompt?: string; print?:
   await proc.exited
 }
 
-/** Open an interactive fish shell in the container. */
-export async function shell(): Promise<void> {
-  const proc = Bun.spawn(
-    ["container", "exec", "-it", "--user", USER, CONTAINER_NAME, "env", "TERM=xterm-256color", "fish", "--login"],
-    { stdin: "inherit", stdout: "inherit", stderr: "inherit" },
-  )
+/** Open an interactive fish shell in the container, optionally in a specific directory. */
+export async function shell(workdir?: string): Promise<void> {
+  const args = ["container", "exec", "-it", "--user", USER]
+  if (workdir) args.push("--workdir", containerPath(workdir))
+  args.push(CONTAINER_NAME, "env", "TERM=xterm-256color", "fish", "--login")
+  const proc = Bun.spawn(args, { stdin: "inherit", stdout: "inherit", stderr: "inherit" })
   await proc.exited
 }