Now and then, a group of enemies in a tunnel

Tunnels are wide enough to fight in now, so occasionally one is occupied:
each tunnel leg rolls a 10% chance of a group of two or three of one kind,
standing within two tiles of each other. Most legs are too short or too
near the entrance to qualify, so in practice it is about one depth-1 run
in three (60 of 200 measured), rising with depth as tunnels get longer.

Rare on purpose -- tunnels are where you go between fights, and a tunnel
that is usually empty is what makes the one that is not a surprise.

Never within aggro range of the entrance, checked per member rather than
per group: members stand up to two tiles off the group's centre, so a
centre that clears the entrance does not mean everyone does. The first
version checked the centre, and the nearest member landed 15 units
outside aggro range by luck. Never a lone straggler: a leg that cannot
fit two gets nobody. Placed after every room, so each room's population
is exactly what its seed always produced, and every leg rolls the same
dice whether or not it is used, so one tunnel's luck never depends on
another's shape. Scaled by the dungeon like every other spawn, each
member from its own fresh definition.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -92,6 +92,7 @@ against itself.
 | Hand-authored boss arenas and hub | done | [src/content/rooms.gd](../src/content/rooms.gd) |
 | Walls, pillars, pits, barricades | done | `MapGrid.Kind` + the three `BLOCKS_*` tables |
 | Enemies placed per room at creation | done | `Instance._populate()` |
+| Occasional enemy groups in tunnels | done | `Instance._populate_tunnels()` — about one depth-1 run in three, never within aggro range of the entrance |
 | Scrolling camera | done | [src/view/game_scene.gd](../src/view/game_scene.gd) |
 | Hard fog of war, lit by rays rather than per tile | done | [src/view/visibility.gd](../src/view/visibility.gd), `WorldView._draw_darkness` |
 | Per-peer map streaming (anti map-hack) | done | `ServerRuntime._stream_map` |