Plan-backed sandboxes now add a masterplan label to the worktree path and plan slug while keeping the branch and change slug stable. The plan scaffold now creates role prompt.md files plus ownership, collaboration, and cleanup-blocking checklist sections, and codex-agent preserves the same naming in both the normal and fallback launch paths.

Constraint: Joined agents must reuse the owner worktree without stealing cleanup ownership from the change lane
Rejected: Prefix the git branch name itself with masterplan | branch identities stay stable while the worktree and plan workspace carry the planning label
Confidence: high
Scope-risk: moderate
Directive: Keep agent-branch-start, codex-agent, and init-plan-workspace naming logic aligned across runtime and template copies
Tested: bash -n scripts/agent-branch-start.sh templates/scripts/agent-branch-start.sh scripts/codex-agent.sh templates/scripts/codex-agent.sh scripts/openspec/init-plan-workspace.sh templates/scripts/openspec/init-plan-workspace.sh; node --test --test-name-pattern "setup agent-branch-start supports optional OpenSpec auto-bootstrap toggles|codex-agent launches codex inside a fresh sandbox worktree and keeps branch/worktree by default|codex-agent restores local branch and falls back to safe worktree start when starter script switches in-place|OpenSpec plan workspace scaffold creates expected role/task structure" test/install.test.js; node --test --test-name-pattern "critical runtime helper scripts stay in sync with templates" test/metadata.test.js; node --test --test-name-pattern "merge branches replays non-conflicting changes onto a dedicated target lane" test/merge-workflow.test.js; openspec validate agent-codex-ralplan-masterplan-role-prompts-and-owne-2026-04-21-14-48 --type change --strict; openspec validate --specs
Not-tested: live GitHub PR merge flow before this commit