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/plugin.rs

@@ -1554,9 +1554,23 @@ mod tests {
         );
 
         // Ground truth: derive_at_metres at the SAME settlement world metres,
-        // via the terrain cache's own re-derive path (run_layer1) so the
-        // TerrainAnalysis is byte-identical to what the resolver used.
-        let (_l1, ta) = crate::atlas::layer1::run_layer1(&heightmap);
+        // via the terrain cache's own re-derive path so the TerrainAnalysis is
+        // byte-identical to what the resolver used — INCLUDING which hydrology
+        // moisture ceiling gets solved with. `resolve_settlement_morphology_zone`
+        // threads `Some(&body_params)` into `get_or_derive` (T-1184), which
+        // derives the body's real moisture ceiling rather than falling back to
+        // `run_layer1`'s body-agnostic default; this ground truth must use the
+        // SAME `run_layer1_with_moisture` path (not bare `run_layer1`) or the
+        // two `TerrainAnalysis`es solve hydrology at different moisture inputs
+        // — moot for this fixture's LAKE EXTENT (moisture-independent, see
+        // `run_layer1_with_moisture_changes_endorheic_split_not_lake_extent`),
+        // but the two paths must agree by construction, not by coincidence of
+        // this specific body having no moisture-sensitive basin near the
+        // sampled position.
+        let (_l1, ta) = crate::atlas::layer1::run_layer1_with_moisture(
+            &heightmap,
+            district_profile::derive_moisture_ceiling_q(&body_params),
+        );
         let expected = district_profile::derive_at_metres(
             body_seed,
             "TestBody",