[squad:plan] Lattice Hollow — M2 Vertical Slice: "First Bloom" (Keaton)

**Owner:** Keaton — Lead/Architect

Part of the Lattice Hollow plan (#58481).

Goals:
- Define the game's final-feel target with one polished multi-room sector.
- Deliverables: representative art direction, one upgrade, one narrative beat, environmental revival payoff.
- Design constraints for pacing, readability, and puzzle onboarding.
- Cross-discipline acceptance criteria for engineering, art, and release readiness.

Depends on #58475 completion outputs.

Start by reviewing the Lattice Hollow plan in #58481 and the completion outputs required by #58475. This issue is a cross-discipline planning milestone rather than a file-specific task; done means defining the polished multi-room sector, upgrade, narrative beat, environmental revival payoff, pacing and puzzle-onboarding constraints, plus acceptance criteria for engineering, art, and release readiness.

Written by the indexing model from the issue text.