Dungeon venue: grid-first traversable dungeon with cast, loot and encounters

New VenueGenerator 'dungeon' archetype. The floor plan is generated first
on a 44x44 grid (rejection-sampled rooms, Kruskal MST + loop edges,
L-shaped corridors, BFS-verified connectivity); walls are merged runs
built exactly where open meets solid, so the shell has no holes, and
the walk route is a closed travelling tour through every room.

The camera either walks first-person (hero hidden to avoid clipping) or
plants on a per-room watch cell with line-of-sight to the route and
tracks the actor. Enemies (walker/structure/swarm ActorSpecs from the
track's own summary) lurk, stand sentry, dart and drift; loot caches
pause the analytic odometer, which can hold or advance but never retreat.

Includes dungeon-debug.html (2D map + timeline stills), 14 map tests
plus facade camera tests, and the portcullis-holds-for-the-whole-party
regression test.

flow-state/src/venues/dungeon/shared.js

@@ -0,0 +1,58 @@
+// Shared helpers for the dungeon venue submodules (layout / zones / props /
+// hazards). Pure, no THREE, no wall-clock, no Math.random — seeded Rng only,
+// all motion analytic f(t, seed) so seek === playback.
+//
+// A submodule owns ONE portion of the image and the 3D space its objects live
+// in. The facade (../dungeon.js) owns the single walk clock and the path;
+// every submodule reads (t, plan, pathAt) and never integrates.
+
+import { Rng } from '../../engine/rng.js';
+
+/** Independent seeded stream that never perturbs sibling streams. */
+export function forkDungeon(seed, label) {
+    return new Rng(hashSeed(seed) ^ 0x9e3779b9).fork(String(label));
+}
+
+function hashSeed(seed) {
+    return (seed >>> 0) || 1;
+}
+
+/** Analytic wrap: position of a base offset walking at rate dz after time t. */
+export function streamWrap(s0, t, dz, span) {
+    const s = s0 + t * dz;
+    return s0 + ((((s - s0) % span) + span) % span);
+}
+
+/** Smoothstep 0..1. */
+export function smooth01(x) {
+    const t = Math.max(0, Math.min(1, x));
+    return t * t * (3 - 2 * t);
+}
+
+/**
+ * Crew-style visibility fade: how many of a population with `count` members
+ * show at a continuous level in [0, ~1.1]. Never toggles — pure f(level,index).
+ * Same pattern as ride.js crew fade (DESIGN §4: furniture never hard-toggles
+ * on interpolated state).
+ */
+export function fadeFor(level, index, count, soft = 0.12) {
+    const showIndex = index / Math.max(1, count);
+    return Math.max(0, Math.min(1, (level - showIndex) / soft));
+}
+
+/** Segment kinds the layout planner may emit. */
+export const SEGMENT_KINDS = [
+    'hall',
+    'room',
+    'forest',
+    'wallwalk',
+];
+
+/** Zone names the zone planner may emit (one per section). */
+export const ZONE_NAMES = ['hall', 'room', 'forest', 'wallwalk'];
+
+/** Prop types in the prop library (primitives only, no glTF). */
+export const PROP_TYPES = ['rubble', 'furniture', 'trees', 'rampart', 'torch', 'banner', 'stalagmite'];
+
+/** Hazard types (visual only — the walk sidesteps them). */
+export const HAZARD_TYPES = ['gate', 'gap', 'patrol'];