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/layer_proxy.rs

@@ -3830,6 +3830,20 @@ mod tests {
         assert_eq!(ta_pass1.water_dist, ta_pass2.water_dist);
         assert_eq!(ta_pass1.slope_deg, ta_pass2.slope_deg);
         assert_eq!(ta_pass1.elev_pct, ta_pass2.elev_pct);
+        // T-1184: two independent hydrology solves (each run_layer1 call
+        // solves fresh — no shared HydrologyResult) must also agree
+        // byte-for-byte, extending this test's own "weakest link in the
+        // determinism chain" rationale to the newest field on TerrainAnalysis.
+        let hydro1 = ta_pass1
+            .hydrology
+            .as_ref()
+            .expect("run_layer1 must populate hydrology");
+        let hydro2 = ta_pass2
+            .hydrology
+            .as_ref()
+            .expect("run_layer1 must populate hydrology");
+        assert_eq!(hydro1.elevation, hydro2.elevation);
+        assert_eq!(hydro1.filled, hydro2.filled);
 
         // Now the FULL path: pack a DistrictWindowLayer from each independent
         // TerrainAnalysis and confirm the complete served payload agrees.