feat(simulation): T-1151 window par_iter + T-1150 granularity carrier (five touch points + aliasing tests)

T-1151: build_district_window_layer dispatches one Rayon task per row
(pure derive_window_cell via derive_at_metres), scattered row-major into
the flat arrays; a cfg(test) serial path backs the bit-identical
parallel-vs-serial golden.

T-1150: serde-default window_granularity (1=district, 4=quarter) +
window_min_wl_m on AtlasLayerRequest — additive, no sixth demux shape,
old frames decode unchanged (tested). Quarter mode = full
reclassification at 512m spacing over the same world rect ((4n)x(4n)
cells); WIRE_CAP_CELLS=4096 enforces n*granularity <= cap (quarter
clamps n to 16, the design doc's worked example). Granularity + min_wl
key ALL five touch points: DistrictWindowLayer echo, server FIFO-256
cache key (now a 5-tuple), per-connection coalescing key, client
request codec (omitted-at-default wire fields), client LRU key.

Mandatory aliasing regressions on both ends: identical (body, center, n)
at granularity 1 vs 4 produce distinct cache entries and correct
per-granularity payload shapes (server, 3-thread queue to avoid the
AnalyzeBody thread contention found while writing it) and distinct
client cache keys (gdUnit). Replay fixture regenerated — the layer
struct grew two echoed fields (231->254 bytes, content verified).

Client requests stay district-granularity by default — quarter requests
arrive with T-1153's rung selection.

server/tests/bridge_tcp.rs

@@ -371,6 +371,8 @@ fn single_tick_drains_all_ready_inbound_frames() {
             up_to: CascadeLayer::Topography,
             window_center: None,
             window_n: 0,
+            window_granularity: 0,
+            window_min_wl_m: 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

@@ -7,6 +7,7 @@ use settled_reach_server::atlas::layer_proxy::{
     AtlasLayerResponse, AtlasLayerStatus, DistrictWindowLayer, QuarterFootprintEntry,
     QuarterFootprintLayer, RegionGridLayer, RoadGraphEdge, RoadGraphLayer, RoadGraphNode,
     SettlementEntry, SettlementLayer, SettlementSizeClass, REGION_TEMP_NONE_DC,
+    WINDOW_GRANULARITY_DISTRICT,
 };
 use settled_reach_server::atlas::region_profile::{SeasonPhase, WeatherState};
 use settled_reach_server::atlas::road_graph::RoadNodeKind;
@@ -725,6 +726,8 @@ fn generate_atlas_layer_response_fixtures() {
     let window = DistrictWindowLayer {
         center: (10, -5),
         n: 2,
+        granularity: WINDOW_GRANULARITY_DISTRICT,
+        min_wl_m: 0,
         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