FERRO AXIS — Product brief

A premium mobile disassembly puzzle where every visible metal part can travel only along authored 3D paths. Players expose deeper pieces, change a shared mechanism between X and Z routing, and extract the entire core. Failure is informative contact, never a spent life.

Prototype goal

Prove that one eight-piece puzzle is legible, deterministic, tactile, and visually close to the supplied screenshots on a real iPhone.

Product invariant

Difficulty comes from spatial reasoning and deeper movable layers — not lives, currencies, timers, ads, random failure, or physics luck.

Non-goals for this milestone

• Monetization, ads, consumables, or lives
• Procedural puzzle generation
• Network play or accounts
• A production level catalog
• Physics-authored legality

Epics

E1 — Deterministic puzzle core

• Blocked moves leave state unchanged.
• Open routes advance to extraction; partial routes stop at the last legal node.
• Undo restores the exact prior snapshot.
• Tests cover the critical transitions.

E2 — Moving axis paths

• The selected route changes between X and Z at shared nodes.
• Axis changes validate every active piece before commit.
• Invalid changes show alignment feedback and do not change state.
• The amber ring animates while the old route ghosts briefly.

E3 — Deeper movable layers

• Depth control cycles active pieces in front-to-back order.
• Relevant occluders become translucent for the current selection.
• Selected deep pieces retain a readable cyan route.

E4 — Full-metal presentation

• PBR metal uses distinct brushed steel, titanium, aluminum, and ceramic-dark presets.
• Cyan, amber, and red each have exactly one semantic job.
• The default framing and HUD match the reference hierarchy.

E5 — Device-ready vertical slice

• The app builds for iPhone simulator.
• Tests pass.
• Touch targets pass a manual phone and tablet review.
• Reduced Motion has an authored fallback.
• Frame pacing remains smooth on the agreed minimum device.