feat(simulation): #523 add zone_id to ObserverSnapshot (D-077, protocol v11)

Server-tracked zone_id on VisibleTile for D-073 zone crossfade and
D-059 deep fog temperature tint. ZoneMap resource backed by BTreeMap,
observer enrichment in snapshot assembly. Backwards-compatible: v10
payloads deserialize with zone_id: None.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/bridge/text_renderer.rs

@@ -268,6 +268,7 @@ mod tests {
                 z: 0,
                 visibility: VisibilitySector::Forward,
                 tile_kind: TileKind::Floor,
+                zone_id: None,
             }],
             nearby_interactions: vec![NearbyInteraction {
                 entity_id: 100,

server/src/bridge/types.rs

@@ -15,7 +15,7 @@ pub use crate::simulation::time::{DayPhase, TickRate};
 /// negotiation is unnecessary. Client should reject snapshots with version !=
 /// PROTOCOL_VERSION. New fields use #[serde(default)] only during the migration
 /// period, then the default is removed once both sides are updated.
-pub const PROTOCOL_VERSION: u8 = 10;
+pub const PROTOCOL_VERSION: u8 = 11;
 
 /// The ONLY data structure crossing the client-server boundary (D-020)
 /// Contains all information visible to the observer at a given tick.
@@ -30,10 +30,11 @@ pub const PROTOCOL_VERSION: u8 = 10;
 /// v9 adds: blocked_entities (#514, debug field for LOS-blocked entities).
 /// v10 adds: sound_events (#124, D-038 server sound event pipeline),
 ///           rng_seed (#527, deterministic replay — completes WRONG button loop).
+/// v11 adds: zone_id on VisibleTile (#523, D-077 OQ-09 resolution + D-073 crossfade).
 /// Future fields: ambient sound events, HUD state (D-020 expansion).
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ObserverSnapshot {
-    /// Protocol version for forward compatibility. Current: 10.
+    /// Protocol version for forward compatibility. Current: 11.
     pub version: u8,
     /// Simulation tick when this snapshot was produced
     pub tick: u64,
@@ -209,6 +210,13 @@ pub struct VisibleTile {
     /// Tile type for client rendering (floor, wall, door, object)
     #[serde(default)]
     pub tile_kind: TileKind,
+    /// Zone identifier for this tile (D-077 OQ-09, D-073 crossfade).
+    /// Server-authoritative zone assignment. Client maps zone_id to:
+    ///   - Audio crossfade target (D-073)
+    ///   - Deep fog temperature tint (D-059 layer 3)
+    /// None for tiles outside any defined zone (corridors, transition spaces).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub zone_id: Option<u16>,
 }
 
 /// Tile type for rendering. Derived from WalkabilityMap on the server side.

server/src/perception/observer/mod.rs

@@ -26,6 +26,7 @@ use crate::simulation::rng::SimRng;
 use crate::simulation::sound::SoundEventQueue;
 use crate::simulation::stance::Stance;
 use crate::simulation::time::SimulationTime;
+use crate::simulation::zone::ZoneMap;
 
 /// Compute visibility geometry using the active perception mode.
 /// Stage 1 of the observer pipeline: FOV + vision cone → VisibilityGeometry.
@@ -61,6 +62,7 @@ pub fn compute_observer_snapshot(
     time: Res<SimulationTime>,
     geometry: Res<VisibilityGeometry>,
     registry: Res<EntityRegistry>,
+    zone_map: Option<Res<ZoneMap>>,
     sound_queue: Option<Res<SoundEventQueue>>,
     mut observer_query: Query<
         (
@@ -221,6 +223,19 @@ pub fn compute_observer_snapshot(
     // Sort entities by entity_id for deterministic snapshot ordering (#457)
     entities.sort_by_key(|e| e.entity_id);
 
+    // Enrich tiles with zone_id from ZoneMap (D-077, D-073)
+    let visible_tiles = match zone_map.as_deref() {
+        Some(zm) => geometry
+            .visible_tiles
+            .iter()
+            .map(|t| VisibleTile {
+                zone_id: zm.zone_at(t.x, t.y, t.z),
+                ..t.clone()
+            })
+            .collect(),
+        None => geometry.visible_tiles.clone(),
+    };
+
     buffer.snapshot = Some(ObserverSnapshot {
         version: crate::bridge::types::PROTOCOL_VERSION,
         tick: time.tick,
@@ -229,7 +244,7 @@ pub fn compute_observer_snapshot(
         player_stance: stance_opt.map(|s| s.0).unwrap_or_default(),
         player_inventory,
         entities,
-        visible_tiles: geometry.visible_tiles.clone(),
+        visible_tiles,
         nearby_interactions,
         current_monologue,
         pending_recognitions,

server/src/perception/query.rs

@@ -83,6 +83,7 @@ impl PerceptionQuery for NaturalVision {
                     z,
                     visibility: sector,
                     tile_kind,
+                    zone_id: None,
                 }
             })
             .collect();

server/src/simulation/mod.rs

@@ -19,6 +19,7 @@ pub mod sound;
 pub mod stance;
 pub mod tier;
 pub mod time;
+pub mod zone;
 
 /// Core simulation plugin
 /// Manages simulation time, RNG, input processing, and tier transitions

server/src/simulation/zone.rs

@@ -0,0 +1,83 @@
+//! Zone map — spatial zone assignment for tiles (D-077, D-073).
+//!
+//! Maps tile coordinates to zone identifiers. Used by:
+//!   - Observer snapshot: enriches VisibleTile with zone_id
+//!   - Client AudioManager: zone crossfade triggers (D-073)
+//!   - Client fog shader: deep fog temperature tint (D-059 layer 3)
+//!
+//! BTreeMap per D-010 principle 4 (deterministic iteration).
+
+use std::collections::BTreeMap;
+
+use bevy_ecs::prelude::*;
+
+/// Server-authoritative zone assignment for tiles.
+///
+/// Each tile position maps to a zone ID. Tiles outside any defined zone
+/// (corridors, transition spaces) have no entry and return None.
+///
+/// Zone IDs are opaque u16 values — the client maintains its own
+/// `zone_id → zone_name / temperature_tint / ambient_layer` mapping.
+#[derive(Resource, Debug, Default)]
+pub struct ZoneMap {
+    zones: BTreeMap<(i32, i32, i32), u16>,
+}
+
+impl ZoneMap {
+    /// Look up the zone for a tile position.
+    pub fn zone_at(&self, x: i32, y: i32, z: i32) -> Option<u16> {
+        self.zones.get(&(x, y, z)).copied()
+    }
+
+    /// Assign a zone to a rectangular region of tiles.
+    /// Used by map builders to define zone boundaries.
+    pub fn set_rect(&mut self, ox: i32, oy: i32, w: i32, h: i32, z: i32, zone_id: u16) {
+        for y in oy..(oy + h) {
+            for x in ox..(ox + w) {
+                self.zones.insert((x, y, z), zone_id);
+            }
+        }
+    }
+
+    /// Assign a zone to a single tile.
+    pub fn set(&mut self, x: i32, y: i32, z: i32, zone_id: u16) {
+        self.zones.insert((x, y, z), zone_id);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn zone_at_returns_none_for_unset_tile() {
+        let map = ZoneMap::default();
+        assert_eq!(map.zone_at(10, 20, 0), None);
+    }
+
+    #[test]
+    fn set_rect_populates_zone() {
+        let mut map = ZoneMap::default();
+        map.set_rect(5, 10, 3, 2, 0, 42);
+
+        // Inside rect
+        assert_eq!(map.zone_at(5, 10, 0), Some(42));
+        assert_eq!(map.zone_at(7, 11, 0), Some(42));
+
+        // Outside rect
+        assert_eq!(map.zone_at(4, 10, 0), None);
+        assert_eq!(map.zone_at(8, 10, 0), None);
+        assert_eq!(map.zone_at(5, 12, 0), None);
+
+        // Wrong z-level
+        assert_eq!(map.zone_at(5, 10, 1), None);
+    }
+
+    #[test]
+    fn set_single_tile() {
+        let mut map = ZoneMap::default();
+        map.set(3, 7, 0, 99);
+        assert_eq!(map.zone_at(3, 7, 0), Some(99));
+        assert_eq!(map.zone_at(3, 8, 0), None);
+    }
+}