feat(hexmap): hex maze generator and digger (L5) - #129

Summary

Lot L5 of origami_hexmap: Mazer::generate, Digger::corridor and Digger::maze.

• Mazer: randomised backtracker over the 6 directions, interior only. A candidate is tested with one mask test maze & 2^c * K (K: field constant per direction and parity). Only the 3 forward neighbours of a tile are candidates (the other two touch its parent), and a carved middle candidate excludes both sides without a test. The direction logic is specialised at compile time (Heading impls).
  • Order 0: the current tile is the candidate's only open neighbour (one-tile corridors and walls).
  • Order 1: in addition, no open tile lies at distance 2 of the candidate except the three tiles behind the current one. So two open tiles at distance 2 always share an open neighbour, and corridors never run side by side. Pictures are in the doc comment.
  • Order >= 2: panics with Mazer: order > 1 not supported (same message as origami_map). The order is asserted once.
• Digger: opens the edge entrance (not a corner), steps to an interior neighbour (an open one if any, otherwise drawn at random), then digs with the same rule against its own tiles. As soon as a dug tile touches an open tile of the grid, corridor stops and maze merges the grid and keeps growing.

Gas (17x14, sierra gas)

Every variant from the brief is implemented and measured in tests/bench_mazer.cairo: explicit stack +51 %, per-neighbour bit tests +220 %, felt maze +1.9 %, DivRem coordinates +12.4 %, lazy draws +7.4 %, shuffle6 +199 %, rotation order -1.7 % per tile (not adopted: below 2 % and biased). Iteration history is in GAS.md.

Tests

• Exact grids on fixed seeds (drawings in comments) for 17x14, 19x13, 7x7 and 3x3, both orders. Digger in both modes.
• Invariants: interior only, determinism, 83x3 and 3x83 extremes, connectivity by flood fill on Layout::expand, tree property (edges = tiles - 1), the order-1 distance-2 rule, and every carve mask checked against its definition from Geometry::distance.
• Digger: every non-corner edge of 7x7 and 3x3, and corridor == maze when nothing is reachable.
• Panics: order, corner, non-edge, dimensions.

Deviation

The digger stops (or merges) when a dug tile touches the open area. origami_map stops when it steps onto it. On hexes, touching already means connected; stepping onto it made corridors run along the room before entering it.

🤖 Generated with Claude Code