feat(simulation): T-1119 QuarterFootprintLayer — server half (touch points 1-2) + populated wire fixtures

ZoningType gains PartialOrd/Ord (DistrictType T-994 mirror) for the
dominant_zoning declaration-order tie-break. layer_proxy:
QuarterFootprintEntry/QuarterFootprintLayer (BTreeMap keyed by
city_id; density_avg_pct floor-mean, dominant_* mode with
declaration-order tie-break, landmark/corridor counts) +
build_quarter_footprint_layer gated None on empty state.quarters;
sixth AtlasLayerResponse field wired into all construction sites;
growth-ceiling doc updated to say the whole-body budget is consumed
(what carries a seventh is T-1124's design, resolved in the same
branch's amendment). Placements whose derived Layer4Quarter id is not
yet in state.quarters are SKIPPED (skeleton gen is async Low-priority
— entries may be a proper subset; client decodes defensively). Stale
TODO(#957) removed (premise predates T-957 landing).

Tie-break bug caught by its own test: Iterator::max_by_key over a
BTreeMap returns the LAST max on ties — backwards from
declaration-order-first; replaced with an explicit forward walk that
replaces only on strictly-greater count.

gen_fixtures: populated RegionGridLayer (T-1118 replay coverage) +
QuarterFootprintLayer literals in the ready fixture; msgpack fixtures
regenerated via make fixtures. Note: landmark_count is inert on real
data today (BlockSkeleton.landmark hardcoded None until landmark
placement lands); fixtures use non-zero counts to exercise the logic.

5 new unit tests + populated round-trip; atlas:: 549 green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/tests/gen_fixtures.rs

@@ -4,16 +4,20 @@
 use settled_reach_server::atlas::body_world_state::{DrainageBasin, RiverNetwork};
 use settled_reach_server::atlas::layer1::Layer1Output;
 use settled_reach_server::atlas::layer_proxy::{
-    AtlasLayerResponse, AtlasLayerStatus, RoadGraphEdge, RoadGraphLayer, RoadGraphNode,
-    SettlementEntry, SettlementLayer, SettlementSizeClass,
+    AtlasLayerResponse, AtlasLayerStatus, QuarterFootprintEntry, QuarterFootprintLayer,
+    RegionGridLayer, RoadGraphEdge, RoadGraphLayer, RoadGraphNode, SettlementEntry,
+    SettlementLayer, SettlementSizeClass,
 };
+use settled_reach_server::atlas::region_profile::{SeasonPhase, WeatherState};
 use settled_reach_server::atlas::road_graph::RoadNodeKind;
 use settled_reach_server::bridge::types::*;
 use settled_reach_server::simulation::generator::{
-    AttractorType, GeographicAttractor, MaintenanceAuthority, SubBiomeVariant,
+    AttractorType, DistrictType, GeographicAttractor, MaintenanceAuthority, SubBiomeVariant,
+    ZoningType,
 };
 use settled_reach_server::simulation::poi::PoiCategory;
 use settled_reach_server::simulation::time::{DayPhase, TickRate};
+use std::collections::BTreeMap;
 use std::fs;
 use std::path::Path;
 
@@ -616,6 +620,53 @@ fn generate_atlas_layer_response_fixtures() {
             },
         ],
     };
+    // T-1113: a small populated RegionGridLayer — a 2×1 covering grid, one
+    // temperate region and one airless-style region (mean_temp_dc sentinel),
+    // mirroring the values exercised by
+    // `build_region_grid_encodes_dense_quantized_climate` in layer_proxy.rs.
+    let region_grid = RegionGridLayer {
+        cols: 2,
+        rows: 1,
+        season: vec![SeasonPhase::Summer as u8, SeasonPhase::Winter as u8],
+        weather: vec![WeatherState::Clear as u8, WeatherState::Snow as u8],
+        mean_temp_dc: vec![
+            123,
+            settled_reach_server::atlas::layer_proxy::REGION_TEMP_NONE_DC,
+        ],
+        moisture_q: vec![80, 5],
+    };
+    // T-1119 (D-226 T-1112 amendment): a populated QuarterFootprintLayer
+    // covering both fixture settlements — city_id 1 (Port Aldren, a dense
+    // Commercial-dominant quarter with landmarks/corridors) and city_id 2
+    // (Farmstead Rell, a sparse Residential-dominant quarter with neither),
+    // so the fixture exercises both a "rich" entry and a "minimal" entry
+    // rather than only one shape.
+    let quarter_footprints = QuarterFootprintLayer {
+        entries: BTreeMap::from([
+            (
+                1,
+                QuarterFootprintEntry {
+                    city_id: 1,
+                    density_avg_pct: 62,
+                    dominant_district_type: DistrictType::Commercial,
+                    dominant_zoning: ZoningType::Commercial,
+                    landmark_count: 3,
+                    corridor_count: 4,
+                },
+            ),
+            (
+                2,
+                QuarterFootprintEntry {
+                    city_id: 2,
+                    density_avg_pct: 18,
+                    dominant_district_type: DistrictType::Residential,
+                    dominant_zoning: ZoningType::Residential,
+                    landmark_count: 0,
+                    corridor_count: 1,
+                },
+            ),
+        ]),
+    };
 
     let ready = AtlasLayerResponse {
         body_id: "GJ1c".into(),
@@ -624,7 +675,8 @@ fn generate_atlas_layer_response_fixtures() {
         district_grid: None,
         road_graph: Some(road_graph),
         settlements: Some(settlements),
-        region_grid: None,
+        region_grid: Some(region_grid),
+        quarter_footprints: Some(quarter_footprints),
     };
     write_fixture(
         "atlas_response_ready",
@@ -639,6 +691,7 @@ fn generate_atlas_layer_response_fixtures() {
         road_graph: None,
         settlements: None,
         region_grid: None,
+        quarter_footprints: None,
     };
     write_fixture(
         "atlas_response_pending",
@@ -653,6 +706,7 @@ fn generate_atlas_layer_response_fixtures() {
         road_graph: None,
         settlements: None,
         region_grid: None,
+        quarter_footprints: None,
     };
     write_fixture(
         "atlas_response_not_found",