Feature request: --rm flag for ephemeral sandboxes

[DevOpsAIguru123]

Summary

Add a --rm flag to sbx create and/or sbx run that automatically removes the sandbox after the session or command exits — equivalent to docker run --rm.

Motivation

Running a one-shot command in a sandbox currently requires a manual 3-step workaround:

NAME=ephemeral-$$ && \
  sbx create shell . --name $NAME --quiet && \
  sbx exec $NAME echo "Hello" ; \
  sbx rm $NAME

This is error-prone (forgetting cleanup leaves ghost sandboxes) and verbose for scripting / CI use cases.

Proposed API

# Create and exec, auto-remove on exit
sbx create --rm shell .

# Or on run
sbx run --rm shell . -- my-command

Expected behavior

• Sandbox is removed immediately after the command/session exits
• Removal happens even if the command fails (mirrors docker run --rm semantics)
• Works with all agents: shell, claude, codex, etc.

Current workaround

Chain with ; (not &&) to guarantee cleanup on both success and failure:

NAME=ephemeral-$$ && \
  sbx create shell . --name $NAME --quiet && \
  sbx exec $NAME <command> ; \
  sbx rm $NAME

Environment

• sbx version: v0.23.0
• OS: macOS (Darwin 25.2.0, aarch64)