feat(simulation): lakes from settled hydrology (D-227, T-1184)

Productionizes the T-1177 equilibrium solver: run_layer1 now solves
hydrology once per body (~24ms, mirrors drainage::analyze) and carries
it as TerrainAnalysis.hydrology; run_layer1_with_moisture threads the
real body moisture ceiling (extracted derive_moisture_ceiling_q), with
the T-1177 population-survey default as fallback. The resident rung-0
global tier does not exist yet (T-1181's scope) — hydrology rides
TerrainAnalysis and lands in that tier for free when it is built
(deviation recorded on the ticket).

MorphologyZone::Lake is now sourced from the settled solver at derive
time: a gridunit is Lake when bilinear-sampled filled surface exceeds
bilinear-sampled original elevation at the sample's own (px, py) — the
continuous comparison, so lake edges refine with rung like coastlines;
never a discrete basin-cell projection. The gate sits strictly between
OpenOcean (>= 80) and the old ocean_fraction heuristic (>= 60), which
survives as the derive-fresh fallback when no solve is attached —
byte-identical to pre-T-1184 output in that case. Static
classification, distinct from the sim-state flooded plane; no
endorheic bit (the drains-vs-closed cue is T-1185's outlet-course
presence, per the D-227 amendment (4) sequencing). Zero new wire
bytes.

Acceptance: lake_classification_cache_hit_equals_cache_miss (solve
twice independently, byte-identical zones, non-vacuous Lake hit) plus
hydrology determinism tests. Golden fidelity: the window golden
fixture now builds TerrainAnalysis through the production entry point
(run_layer1_with_moisture, per-body), and a dedicated lake_bowl golden
body pins the hydrology-sourced Lake path (morphology 1 at
ocean_fraction_q 0 — provably not the heuristic); the 108 pre-existing
golden rows are byte-identical (pure append). believability.json moved
by one lake-shaped line (GJ338Bd voxel_relief_m 27->28, a correctly
reclassified lake district leaving the dry-relief sample set).
river_course and derivation-harness goldens unchanged. Full suite:
2114 passed.

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

server/src/atlas/cascade.rs

@@ -252,8 +252,22 @@ pub fn run_cascade_from_heightmap(
     // run_layer1 now returns (Layer1Output, TerrainAnalysis); the TerrainAnalysis
     // is carried transiently on the snapshot so DistrictProfile + RoadGraph can
     // reuse it without the former ~45 ms redundant drainage re-run (T-1044).
+    //
+    // T-1184: settled-equilibrium hydrology solves inside run_layer1 as part
+    // of this same pass (D-227 amendment (4), the AnalyzeBody cascade populate
+    // point). When real BodyParams are available, derive the body's actual
+    // moisture ceiling (hydrosphere/atmosphere) for the endorheic-vs-overflow
+    // split rather than falling back to run_layer1's body-agnostic default —
+    // this cascade entry point always has body_params in scope when the
+    // caller supplied one, so there is no reason to leave it on the fallback.
     if up_to >= CascadeLayer::Topography {
-        let (mut l1, ta) = layer1::run_layer1(&snapshot.heightmap);
+        let (mut l1, ta) = match body_params {
+            Some(params) => layer1::run_layer1_with_moisture(
+                &snapshot.heightmap,
+                district_profile::derive_moisture_ceiling_q(params),
+            ),
+            None => layer1::run_layer1(&snapshot.heightmap),
+        };
         // Stamp the province TerritorialStatus (D-212) onto each basin.
         for basin in &mut l1.drainage_basins {
             basin.territorial_status = territorial_status.clone();