Problem

When using sbx with --branch, gitignored files (.env, local.settings.json, etc.) are excluded. These files are almost always required to run or test a project locally. There is currently no way to carry them into a sandbox branch without manual intervention.

Proposed Solution: .worktreeinclude file

Claude Code already implements this pattern for git worktrees: if a .worktreeinclude file exists in the repository root, Claude copies all listed files/patterns into each new worktree — preserving directory structure — even if they are gitignored.

Example .worktreeinclude:

.env
local.settings.json
.autoflow

sbx could adopt the same convention: when creating a sandbox from a branch, detect .worktreeinclude and bind/copy those files into the sandbox environment.

Benefits:

• Declarative and repo-local — the include list is tracked in git, the secrets are not
• Zero per-invocation flags required
• Follows an established pattern from Claude Code tooling
• Works naturally with .gitignore (secrets stay out of git, but reach the sandbox)