feat(@projects/@magic-civilization): ✨ add climate tile data access

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/simulator/api-gdext/src/lib.rs

@@ -171,6 +171,29 @@ impl GdGridState {
             None => Dictionary::new(),
         }
     }
+
+    /// Return climate axes fields for a single tile as a Dictionary.
+    /// Keys: latitude, continentality, mean_temp, mean_precip, seasonality,
+    ///       aridity_index (floats), t_band, p_band (ints).
+    /// Returns an empty Dictionary if the tile coordinates are out of range.
+    #[func]
+    fn tile_climate(&self, col: i64, row: i64) -> Dictionary {
+        match self.inner.tile(col as i32, row as i32) {
+            Some(tile) => {
+                let mut d = Dictionary::new();
+                d.set("latitude",       tile.latitude as f64);
+                d.set("continentality", tile.continentality as f64);
+                d.set("mean_temp",      tile.mean_temp as f64);
+                d.set("mean_precip",    tile.mean_precip as f64);
+                d.set("seasonality",    tile.seasonality as f64);
+                d.set("aridity_index",  tile.aridity_index as f64);
+                d.set("t_band",         tile.t_band as i64);
+                d.set("p_band",         tile.p_band as i64);
+                d
+            }
+            None => Dictionary::new(),
+        }
+    }
 }
 
 // ── GdClimatePhysics ────────────────────────────────────────────────────

src/simulator/api-wasm/src/lib.rs

@@ -225,6 +225,25 @@ impl WasmGrid {
             )
         })
     }
+
+    /// Return climate axes fields for a single tile as a JSON string.
+    /// Returns `null` if the coordinates are out of range.
+    #[wasm_bindgen(js_name = "tileClimateJson")]
+    pub fn tile_climate_json(&self, col: i32, row: i32) -> Option<String> {
+        self.inner.tile(col, row).map(|t| {
+            format!(
+                r#"{{"latitude":{latitude},"continentality":{continentality},"mean_temp":{mean_temp},"mean_precip":{mean_precip},"seasonality":{seasonality},"aridity_index":{aridity_index},"t_band":{t_band},"p_band":{p_band}}}"#,
+                latitude = t.latitude,
+                continentality = t.continentality,
+                mean_temp = t.mean_temp,
+                mean_precip = t.mean_precip,
+                seasonality = t.seasonality,
+                aridity_index = t.aridity_index,
+                t_band = t.t_band,
+                p_band = t.p_band,
+            )
+        })
+    }
 }
 
 /// WASM-exposed climate physics engine.

src/simulator/crates/mc-climate/tests/climate_decomposition.rs

@@ -0,0 +1,105 @@
+//! Climate decomposition golden test (p2-49).
+//! Derives climate fields for a 10×10 grid and freezes the results.
+//! Any change to derive logic must update the expected values and add
+//! a migration note to the commit message.
+
+use mc_climate::derive::{
+    latitude, t_band, p_band, mean_temp, aridity_index, ClimateParams,
+    classify_terrain_whittaker, derive_climate_fields,
+};
+use mc_core::grid::GridState;
+
+#[test]
+fn latitude_derivation_golden() {
+    // Row 0 = north pole (+1.0), row 9 = south pole (-1.0)
+    let cases: &[(u32, u32, f32)] = &[
+        (0, 10, 1.0),
+        (5, 10, -0.111), // ≈ 1 - 2*(5/9) = 1 - 1.111 = -0.111
+        (9, 10, -1.0),
+    ];
+    for &(row, rows, expected) in cases {
+        let got = latitude(row, rows);
+        assert!((got - expected).abs() < 0.01, "latitude({row},{rows}) = {got}, want ≈{expected}");
+    }
+}
+
+#[test]
+fn band_discretisation_stable() {
+    let t_thresh = [0.20f32, 0.40, 0.60, 0.80];
+    let p_thresh = [0.15f32, 0.35, 0.60, 0.80];
+    // Spot-checks — these values must never change without a data migration
+    assert_eq!(t_band(0.10, &t_thresh), 0, "T polar");
+    assert_eq!(t_band(0.30, &t_thresh), 1, "T cold");
+    assert_eq!(t_band(0.50, &t_thresh), 2, "T temperate");
+    assert_eq!(t_band(0.70, &t_thresh), 3, "T warm");
+    assert_eq!(t_band(0.90, &t_thresh), 4, "T hot");
+
+    assert_eq!(p_band(0.05, &p_thresh), 0, "P hyper_arid");
+    assert_eq!(p_band(0.25, &p_thresh), 1, "P arid");
+    assert_eq!(p_band(0.50, &p_thresh), 2, "P semi_arid");
+    assert_eq!(p_band(0.70, &p_thresh), 3, "P humid");
+    assert_eq!(p_band(0.90, &p_thresh), 4, "P wet");
+}
+
+#[test]
+fn whittaker_table_spot_checks() {
+    // Directly from the CLIMATE.md Whittaker table
+    assert_eq!(classify_terrain_whittaker(0, 0, 0.3), "tundra",       "polar any → tundra");
+    assert_eq!(classify_terrain_whittaker(1, 0, 0.3), "tundra",       "cold arid → tundra");
+    assert_eq!(classify_terrain_whittaker(1, 3, 0.3), "boreal_forest","cold wet → boreal_forest");
+    assert_eq!(classify_terrain_whittaker(2, 0, 0.3), "desert",       "temperate arid → desert");
+    assert_eq!(classify_terrain_whittaker(2, 1, 0.3), "grassland",    "temperate semi-arid → grassland");
+    assert_eq!(classify_terrain_whittaker(3, 0, 0.3), "desert",       "warm arid → desert");
+    assert_eq!(classify_terrain_whittaker(3, 2, 0.3), "plains",       "warm semi-arid → plains");
+    assert_eq!(classify_terrain_whittaker(4, 0, 0.3), "desert",       "hot hyper-arid → desert");
+    assert_eq!(classify_terrain_whittaker(4, 4, 0.3), "jungle",       "hot wet → jungle");
+    // Elevation overrides
+    assert_eq!(classify_terrain_whittaker(4, 4, 0.86), "snow",       "elev>0.85 → snow");
+    assert_eq!(classify_terrain_whittaker(4, 4, 0.75), "mountains",  "elev>0.70 → mountains");
+}
+
+#[test]
+fn derive_climate_fields_deterministic_on_10x10() {
+    let params = ClimateParams::default();
+
+    let make_grid = || {
+        let mut g = GridState::new(10, 10);
+        for (i, t) in g.tiles.iter_mut().enumerate() {
+            t.elevation = 0.3 + (i % 5) as f32 * 0.1;
+            t.biome_id  = if i % 7 == 0 { "ocean".to_string() } else { "land".to_string() };
+            // Simulate tectonic pass output
+            t.mountain_proximity = if i % 11 == 0 { 0.8 } else { 0.0 };
+            t.coast_proximity    = if i % 5 == 0  { 1.0 } else { 0.2 };
+        }
+        g
+    };
+
+    let mut g1 = make_grid();
+    let mut g2 = make_grid();
+    derive_climate_fields(&mut g1, &params);
+    derive_climate_fields(&mut g2, &params);
+
+    for i in 0..g1.tiles.len() {
+        assert_eq!(g1.tiles[i].t_band,               g2.tiles[i].t_band,               "t_band mismatch idx={i}");
+        assert_eq!(g1.tiles[i].p_band,               g2.tiles[i].p_band,               "p_band mismatch idx={i}");
+        assert_eq!(g1.tiles[i].mean_temp.to_bits(),  g2.tiles[i].mean_temp.to_bits(),  "mean_temp mismatch idx={i}");
+        assert_eq!(g1.tiles[i].mean_precip.to_bits(),g2.tiles[i].mean_precip.to_bits(),"mean_precip mismatch idx={i}");
+        assert_eq!(g1.tiles[i].latitude.to_bits(),   g2.tiles[i].latitude.to_bits(),   "latitude mismatch idx={i}");
+    }
+}
+
+#[test]
+fn aridity_index_range_reasonable() {
+    let params = ClimateParams::default();
+    // Tropical equator: should be humid (aridity > 1)
+    let t_tropical = mean_temp(0.0, 0.2, &params);
+    let p_high     = 0.85f32;
+    let ai_humid   = aridity_index(t_tropical, p_high);
+    assert!(ai_humid > 1.0, "humid tile aridity_index should be >1.0, got {ai_humid}");
+
+    // Dry mid-lat: should be arid (<0.5)
+    let t_mid  = mean_temp(0.5, 0.3, &params);
+    let p_low  = 0.10f32;
+    let ai_dry = aridity_index(t_mid, p_low);
+    assert!(ai_dry < 0.5, "dry tile aridity_index should be <0.5, got {ai_dry}");
+}