Crafting system (2x2 + 3x3 grid, recipe matching)

[MichaelFisher1997]

Phase 2 foundation. Do this first — smelting (#3), tools (#4) and farming (#5) all build on the recipe registry and slot/UI patterns established here.

Context

The inventory already ships a disabled 2x2 crafting grid placeholder at src/ui/InventoryUI.ts:77-88 — four slot slot-disabled divs with no backing data model. There is no recipe registry and no matcher anywhere in the codebase today.

Scope

• New src/game/Recipes.ts — does not exist. Define:
  • Recipe type supporting shaped (pattern + key→itemId) and shapeless (set of inputs) recipes
  • RECIPES registry array
  • match(grid: (ItemId | null)[]): ItemId | null matcher that scans both 2x2 (inventory) and 3x3 (table) subregions
• src/ui/InventoryUI.ts:77-88 — replace the four slot-disabled divs with interactive craft-input slots and a live output slot that re-resolves on every grid mutation; consume inputs on craft.
• src/game/Inventory.ts — add a craftingGrid: ItemStack[9] field (separate from backpack slots); reuse existing getSlot/setSlot/add/remove helpers (lines 31-91). Persist craft-grid state with the save.
• src/game/Items.ts — register newly craftable item ids (e.g. planks, stick, crafting_table); add to CREATIVE_PALETTE (line 84) and DROP_TABLE (line 114) as needed.
• src/ui/ui.css (~.inv-craft-grid lines 695-712) — drop slot-disabled styling, add hover/active/drag state.
• (Optional, unlock 3x3) Add a crafting_table block — requires touching Blocks.ts + BlockIds.ts + Textures.ts in lockstep per AGENTS.md (block ids must stay stable; atlas is 8x8 = 64 tiles).

Starter recipe set

• 1 log → 4 planks (shapeless)
• 2 planks → 4 sticks (shaped)
• 4 planks → crafting table (shaped)

Acceptance criteria

• Craft-input slots accept dragged items from the backpack; output slot shows the matched result live.
• Crafting consumes inputs and places the result in the held/cursor slot.
• Recipes.ts is exported and unit-testable (pure match() function).
• At least the three starter recipes work end-to-end in survival mode.
• No regressions to existing inventory drag/drop and hotbar behaviour.

Roadmap reference

Phase 2 — "Crafting system".