6. Blockstate Model

6.1 Derive by default + override-promotion (soft boundary)

• By default the compiler derives blockstate from position and neighbors (stair facing, door orientation, glass-pane/fence/wall connections, chest left/right, etc.).
• Any blockstate that can be architectural intent is overridable, and the moment it is written it is promoted to “intent”.
• The strong reading “if it can be derived, don’t let the AI write it” is not adopted. The correct rule is “derive by default; any blockstate that can be intent is overridable.”

Representative cases that MUST be overridable (i.e. can be intent):

• stairs facing (as a chair/decoration the facing itself is intent), stairs half=top (upside-down = eaves), stairs shape
• chest size=single (auto-merging from adjacency is forbidden), bed facing, door hinge/open
• log/pillar axis (a horizontal beam), trapdoor open/half, snow layers, candle count, glazed_terracotta rotation
• redstone_dust connect, repeater delay, observer/piston/dispenser facing, note/instrument

Easy-to-miss cases that belong to derivation: torch↔wall_torch, sign↔wall_sign auto-substitution by attachment face.

stair id=eave   kind=stairs mat_slot=roof side=front half=top facing=out shape=outer_left  # eaves
beam  id=lintel kind=pillar mat_slot=frame at=front.top axis=x                              # horizontal beam
chest id=store  at=inside.back size=single
note_block at=2,1,2 instrument=bit note=12

6.2 IR representation: separate intent_state / resolved_state

member:
  id: eave
  type: block | block_entity | entity      # the distinction is the compiler's job but typed in the IR
  primitive: stairs
  intent_state:   { half: top, shape: outer_left }       # author intent. Edit diffs look only here
  resolved_state: { facing: north, waterlogged: false }  # derived result; paint-derived state goes here

• Named to avoid collision with Minecraft’s term blockstate: intent_state / resolved_state.
• bed is treated as a block member (not an entity, to keep the IR types clean).
• For edit stability, do not mix resolved (derived/paint-origin) with intent (author).

6.3 waterlogged

• Default is paint-derived: when fill fluid=water overlaps a waterloggable block, the compiler sets waterlogged.
• A three-valued waterlogged=auto|true|false is allowed: to leave an air pocket inside a tank (explicit false), to distinguish source/flowing, and for version differences in the waterloggable table.
• Flowing water is made explicit with flow= / level=.

fill fluid=water kind=source from=1,1,1 to=5,3,5    # overlapping fences/stairs/signs auto-waterlogged
trapdoor id=shutter at=.. waterlogged=false          # air window in a tank
water id=stream from=.. flow=east level=4