Doctor should still be usable for setup drift recovery without mutating a protected base checkout in place. This routes doctor to an auto-created sandbox worktree branch when the current branch is protected, then executes doctor there.

Constraint: Protected main must remain pull-only in initialized repositories

Rejected: Keep blocking doctor on protected main entirely | breaks maintenance flow for drifted repos

Confidence: medium

Scope-risk: moderate

Reversibility: clean

Directive: Keep doctor sandbox fallback aligned with agent-branch-start output parsing

Tested: node --check bin/multiagent-safety.js

Not-tested: fully passing suite in this environment