fix(simulation): review follow-ups on foundation types (#1006)

- Derive MorphologyZone Default (#[default] AlluvialPlain), drop manual
  impl — clears the clippy --all-targets warning (pre-push gate).
- Fix floor_at_voxel_z doc (described the inverse function).
- Document floor_at_voxel_z / voxel_range_for_floor voxel-z as
  building-relative (base_floor = z:0) for #982-985 callers.
- TODO(#957): districts keyed by city_id is a stub; use district_id.

clippy --all-targets clean; 1259 lib tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/atlas/gen_queue.rs

@@ -111,10 +111,7 @@ pub enum GenCompletion {
         block_pos: (u32, u32),
     },
     /// Work item failed — body_id or city_id for logging.
-    Failed {
-        item: GenWorkItem,
-        reason: String,
-    },
+    Failed { item: GenWorkItem, reason: String },
 }
 
 // ---------------------------------------------------------------------------

server/src/atlas/plugin.rs

@@ -88,6 +88,8 @@ fn drain_generation_completions(
             } => {
                 if !body_id.is_empty() {
                     if let Some(body_state) = cache.peek_mut(&body_id) {
+                        // TODO(#957): keying by city_id is a stub — a city has multiple districts;
+                        // use DistrictSkeleton.district_id as the DistrictId key when real skeleton gen lands.
                         body_state.districts.insert(city_id, state);
                     } else {
                         tracing::warn!(

server/src/simulation/generator.rs

@@ -555,9 +555,13 @@ impl FloorExtent {
         }
     }
 
-    /// Map a D-110 floor index to the first voxel-z value at that floor's base.
+    /// Map a building-relative voxel-z coordinate to the D-110 floor index that contains it.
     ///
-    /// Returns `None` if `floor_index` is outside `[base_floor, base_floor + floor_count)`.
+    /// Returns the floor index whose voxel span covers `voxel_z`, or `None` if `voxel_z`
+    /// falls outside the building's extent (below base floor or above the topmost floor).
+    ///
+    /// `voxel_z` is building-relative: the base floor maps to z = 0. Callers working in
+    /// world space must subtract the building's world-base z offset before calling this method.
     pub fn floor_at_voxel_z(&self, voxel_z: i32) -> Option<i8> {
         let voxel_z_for_base = self.voxel_z_for_floor(self.base_floor)?;
         if voxel_z < voxel_z_for_base {
@@ -584,6 +588,9 @@ impl FloorExtent {
     /// Map a D-110 floor index to the inclusive voxel-z range `(min_z, max_z)`.
     ///
     /// Returns `None` if `floor_index` is outside the building's extent.
+    ///
+    /// The returned range is building-relative: the base floor maps to z = 0. Callers working
+    /// in world space must add the building's world-base z offset to the returned values.
     pub fn voxel_range_for_floor(&self, floor_index: i8) -> Option<(i32, i32)> {
         let base_z = self.voxel_z_for_floor(self.base_floor)?;
         let relative = floor_index as i16 - self.base_floor as i16;
@@ -741,15 +748,24 @@ pub enum DoorInitialState {
 pub enum DoorCredential {
     None,
     /// Door is only accessible during specified hours (0–23, inclusive range).
-    TemporalWindow { open_hour: u8, close_hour: u8 },
+    TemporalWindow {
+        open_hour: u8,
+        close_hour: u8,
+    },
     /// Requires an employment credential from this corporation.
-    Corporate { corp_id: String },
+    Corporate {
+        corp_id: String,
+    },
     /// Requires a residence credential in this block.
-    Resident { block_id: String },
+    Resident {
+        block_id: String,
+    },
     /// Law-enforcement / government authority only.
     Authority,
     /// Social trust score threshold (basis points; D-010 integer, 10 000 = 1.0).
-    Social { trust_threshold_bps: u32 },
+    Social {
+        trust_threshold_bps: u32,
+    },
 }
 
 /// What a door connects to on the other side (D-231).
@@ -807,7 +823,7 @@ pub struct DoorSpec {
 /// Shared by all tiles in a region; constrains street geometry (D-234)
 /// and acts as a soft weight on cultural-template eligibility (D-232).
 /// Carried on `CityGenerationContext` (D-233 amend to D-199).
-#[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq)]
+#[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq, Default)]
 pub enum MorphologyZone {
     /// Steep-sided inlet — ribbon/hub-and-spoke streets only; pier geometry on water edges.
     Fjord,
@@ -816,6 +832,7 @@ pub enum MorphologyZone {
     /// Meandering river reach — any pattern.
     MeanderReach,
     /// Flat alluvial plain — any pattern; primary default for plains settlements.
+    #[default]
     AlluvialPlain,
     /// Open ocean surface (deep-water context) — hub-and-spoke; perimeter access priority.
     OpenOcean,
@@ -835,12 +852,6 @@ pub enum MorphologyZone {
     Unknown,
 }
 
-impl Default for MorphologyZone {
-    fn default() -> Self {
-        MorphologyZone::AlluvialPlain
-    }
-}
-
 /// Built-form archetype derived from a settlement's dominant commodity (D-233).
 ///
 /// 5 archetypes projected from the 8 cargo-type classifications in `commodities.toml`;