generateBaseTerrain now factors the noise+surface stage out of chunk
generation so structure placement can read pre-carve heights exactly
like vanilla's STRUCTURE_STARTS stage. RuinedPortalGenerationPoint
replays the ruined_portals set: the weighted pick across all seven
variants on its own stream, each attempt's setup/template/rotation/
mirror draws on a fresh GenerationContext stream (makeRandom reseeds
per attempt, confirmed from bytecode), findSuitableY with corner-column
settle scan against those heights, and the post-draw 3D-biome filter at
quart-snapped coordinates.
Known gap, documented in STRUCTURE_NOTES.md: no variant is accepted in
the window around the fixture's portal yet while vanilla placed one;
the biome/surface inputs need a vanilla-side probe to bisect. Not wired
into the production replay until that closes.
LoadResolvedTemplate parses the extracted .nbt files with every palette
entry resolved to concrete state IDs through an injected resolver, and
TransformBlockPos reproduces StructureTemplate.transform's mirror-then-
rotate order around the pivot, including all three quarter-turn cases
read off the bytecode. MthGetSeed gives processors their per-block
positional Legacy stream. Verified against the real ruined_portal
templates: every block lands inside the declared size for all eight
mirror/rotation combinations.
