Summary

• Support entering worktrees whose branch name contains spaces via port enter and the implicit port <branch> form, in all forms: port enter "my feature", port enter my feature, port "my feature", and port my feature.
• Parse branch arguments as variadic positionals and join bare words into a single name (new exported joinBranchArgs helper in src/index.ts).
• Resolve a valid git ref before worktree creation: names git rejects (spaces, etc.) fall back to the sanitized form (my feature → branch my-feature), while valid refs like feature/auth are preserved (new isValidBranchRef / resolveBranchRef in src/lib/git.ts, used by enter.ts). Worktree directory naming and PORT_WORKTREE identity stay sanitized and unchanged.
• Make the test harness space-safe: execPortAsync now uses execFile (no shell) so spaced args and script paths survive (tests/utils.ts, src/lib/exec.ts).
• Add a design doc under docs/superpowers/specs/.

Testing

• joinBranchArgs unit tests (src/index.test.ts); isValidBranchRef / resolveBranchRef unit tests (src/lib/git.test.ts); command-level spaced-branch case (src/commands/enter.command.test.ts); smoke E2E covering explicit and implicit forms (tests/enter-spaces.test.ts).
• Result: targeted test set passing (68 tests across touched files); typecheck clean; lint 0 errors (only pre-existing unrelated warnings); prettier clean.

Risks

• Behavioral change: spaced/invalid branch names now resolve to a sanitized git ref instead of erroring; valid refs (e.g. with slashes) are unaffected.
• None noted for rollout; change is scoped to the enter / implicit entry points and the test harness, with no change to worktree directory or domain/routing identity.

(Drafted by Jacob's coding agent on his behalf)