vision: staged-fork Apply path (preview → apply → rollback); Habit mode embryo

[Zychs]

Vision

Habit / Staged Fork Mode — parallel change paths; sandbox experiments can land without rewriting primary history. Relate Mode anchors SSOT. Spec: docs/specs/radial-rerooting-spec.md (metadata.isStaged / hasChanges surface).

Reality

STUB — modes are speced and deferred past MVP (README.md status words after Phase A honesty pass). No staged write path in src/.

Scope (Phase D)

• Apply targets a staged fork, not primary history.
• Pattern: preview → apply → rollback.
• Staged fork visible in radial with staged styling once radial is wired.
• VERSIONING §7.1 unplugged still holds.

Exit

Sandbox experiment survives into staged state; rollback restores cleanly; primary history untouched.

Depends on

Phase C substrate + gate; preferably Phase B radial for visibility.

Refs

docs/ghm2-development-plan.md Phase D · radial-rerooting-spec staged metadata · VERSIONING §3 Sandbox/Gate tiers