feat(simulation): T-1137 windowed district layer — queue-served, coalesced, determinism-tested (D-226 T-1124 SS1-SS4)

AtlasLayerRequest gains window_center/window_n (serde-default, absent
= whole-body, wire back-compat; demux untouched — up_to stays the
discriminator). DistrictWindowLayer echoes center/n + six parallel
arrays (morphology, elev_q, temp_dc i16 with the region sentinel,
moisture_q, vegetation incl Marine=6, glaciation).

Serving per the amendment's binding model: NEVER inline —
GenWorkItem::DeriveWindow rides the Rayon queue, completion drain
caches into DistrictWindowCache (bounded FIFO 256; no staleness by
D-227 purity, capacity bound only), serve_district_window polls the
cache and returns Pending-shaped None until derived. Per-connection
coalescing: submit_window supersedes a still-pending item for the
same (ConnectionId, body) — the surviving item is the newer one,
proven by dedicated tests.

TerrainAnalysis decision (option b, numbers in ticket/PR): re-derive
via run_layer1 in the DeriveWindow branch rather than caching ~1.5MB
x 50 LRU slots (~100MB permanent, the exact D-203 bloat T-1044's own
text guarded against); ~45ms one-time on the Rayon path, invisible to
the tick thread. T-1044 confirmed within-cascade-only (cascade.rs:358
still drops the analysis before BodyWorldState) — the fork was open.

Window derive loop promoted from aliveness_probe::render_window_panels;
determinism promoted from probe-only proof to a real test (two passes
byte-identical). New fixture atlas_response_ready_with_window
exercises all six arrays incl. the airless sentinel and Marine; three
existing fixtures gain district_window: None. Server clamps window_n
to 1..=DISTRICT_WINDOW_MAX_N=64 (never trust the wire).

1774/1774 lib + 19/19 bridge_tcp green.

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

server/tests/bridge_tcp.rs

@@ -369,6 +369,8 @@ fn single_tick_drains_all_ready_inbound_frames() {
         let req = AtlasLayerRequest {
             body_id: "GJ1c".into(),
             up_to: CascadeLayer::Topography,
+            window_center: None,
+            window_n: 0,
         };
         let payload = rmp_serde::to_vec_named(&req).expect("failed to serialize");
         write_framed(&mut stream, &payload).expect("write atlas frame");

server/tests/gen_fixtures.rs

@@ -4,9 +4,9 @@
 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, QuarterFootprintEntry, QuarterFootprintLayer,
-    RegionGridLayer, RoadGraphEdge, RoadGraphLayer, RoadGraphNode, SettlementEntry,
-    SettlementLayer, SettlementSizeClass,
+    AtlasLayerResponse, AtlasLayerStatus, DistrictWindowLayer, QuarterFootprintEntry,
+    QuarterFootprintLayer, RegionGridLayer, RoadGraphEdge, RoadGraphLayer, RoadGraphNode,
+    SettlementEntry, SettlementLayer, SettlementSizeClass, REGION_TEMP_NONE_DC,
 };
 use settled_reach_server::atlas::region_profile::{SeasonPhase, WeatherState};
 use settled_reach_server::atlas::road_graph::RoadNodeKind;
@@ -676,6 +676,7 @@ fn generate_atlas_layer_response_fixtures() {
         road_graph: Some(road_graph),
         settlements: Some(settlements),
         region_grid: Some(region_grid),
+        district_window: None,
         quarter_footprints: Some(quarter_footprints),
     };
     write_fixture(
@@ -691,6 +692,7 @@ fn generate_atlas_layer_response_fixtures() {
         road_graph: None,
         settlements: None,
         region_grid: None,
+        district_window: None,
         quarter_footprints: None,
     };
     write_fixture(
@@ -706,10 +708,43 @@ fn generate_atlas_layer_response_fixtures() {
         road_graph: None,
         settlements: None,
         region_grid: None,
+        district_window: None,
         quarter_footprints: None,
     };
     write_fixture(
         "atlas_response_not_found",
         &rmp_serde::to_vec_named(&not_found).unwrap(),
     );
+
+    // D-226 T-1124 amendment, T-1137: a Ready response carrying a populated
+    // district_window — the windowed-family field, distinct from the five
+    // whole-body layers above. A small n=2 window keeps the fixture readable
+    // while exercising every field (including the REGION_TEMP_NONE_DC
+    // sentinel and VegetationClass::Marine = 6, both non-negotiable per the
+    // amendment §3).
+    let window = DistrictWindowLayer {
+        center: (10, -5),
+        n: 2,
+        morphology: vec![0, 8, 14, 16], // OpenOcean, AlluvialPlain, Alpine, Wetland
+        elev_q: vec![0, 45, 98, 60],
+        temp_dc: vec![205, 150, REGION_TEMP_NONE_DC, 80], // 20.5°C, 15.0°C, airless sentinel, 8.0°C
+        moisture_q: vec![90, 55, 0, 100],
+        vegetation: vec![6, 3, 0, 5], // Marine, Forest, Absent, RiparianThicket
+        glaciation: vec![0, 0, 4, 1], // None, None, IceCap, Light
+    };
+    let ready_with_window = AtlasLayerResponse {
+        body_id: "GJ1c".into(),
+        status: AtlasLayerStatus::Ready,
+        layer1: None,
+        district_grid: None,
+        road_graph: None,
+        settlements: None,
+        region_grid: None,
+        district_window: Some(window),
+        quarter_footprints: None,
+    };
+    write_fixture(
+        "atlas_response_ready_with_window",
+        &rmp_serde::to_vec_named(&ready_with_window).unwrap(),
+    );
 }