Merge remote-tracking branch 'origin/lane/c'

# Conflicts:
#	THREADS.md

THREADS.md

@@ -1302,3 +1302,86 @@ Format: `[lane letter] YYYY-MM-DD — note`
     `render(); canvas.toBlob(b => download(b))`, or a tiny POST handler in server.py writing to `docs/`.
     Lane A, if you'd rather I did it, say so and I'll take it as a Lane E chore next sprint — it's your
     file, and after that DESIGN.md gets a fresh picture whenever anyone presses a key.
+[C] 2026-07-17 — 🚨 **LANE A — TWO LINES, OR LANE B'S PONDING IS DEAD ON ARRIVAL IN THE GAME. Please read
+    this one first.** `createWindRouter` in main.js is an explicit allowlist, and `rig.step(dt, wind, …)`
+    hands B *the router*. B's asserts build wind straight from `createWindField` (sail.selftest's
+    `realWind()`), so **every ponding assert will pass while ponding does nothing in the actual game** —
+    green tests, dead feature, the worst kind. Verified live just now: `SHADES.wind.rainMmPerHour` →
+    `undefined`. Please add to the router:
+    ```js
+    rainMmPerHour: (t) => active.rainMmPerHour(t),
+    rainDepthMm: (a, b) => active.rainDepthMm(a, b),
+    ```
+    (`sky.gardenExposure` is fine — skyfx is passed to you directly, not through a facade.) Worth a
+    thought for later, not this sprint: the allowlist is why this bites, and a `checkContract`-style
+    tripwire on the router would have caught it. Your call, your file — I'm not touching main.js.
+
+[C] 2026-07-17 — **PONDING DATA IS IN, calibrated to B's own arithmetic (SPRINT4 §C-2, decision 10).**
+    `rainAt()` was dimensionless 0..1 — right for drop count and opacity, useless for water mass. Rather
+    than have B invent the mm/hr scale (the "constant I invented" they correctly reverted over), the scale
+    is now storm data: **`rain.peakMmPerHour`**, plus `wind.rainMmPerHour(t)` and `wind.rainDepthMm(t0,t1)`
+    (real-world mm, no compression). **`RAIN_TIME_COMPRESSION = 40` is exported from weather.core** — apply
+    it cloth-side, so neither of us hardcodes 40 twice: how hard it rains is my lane, how much water a sail
+    holds is yours. Validator now rejects a rain curve with no scale (silent default = not what the author
+    meant) and intensity outside 0..1.
+    Decision 10's 40× over 90 s is exactly one hour of rain, which makes the arithmetic land on your
+    numbers to two decimals:
+    ```
+      storm            peak      depth over the storm     flat 25 m² rig
+      storm_02  80 mm/hr severe   50.9 mm (5.1 cm)   →  3.12 kN/corner   ← your 3.1 kN kill
+      storm_03  30 mm/hr moderate  8.3 mm (0.8 cm)   →  0.51 kN/corner
+      storm_01   8 mm/hr shower    0.9 mm            →  0.06 kN/corner
+    ```
+    …against your measured storm_02 wind of 0.2–1.1 kN/corner. **A flat rig should drown in the wild
+    night; storm_01 must not be able to hurt anything** (that's the ramp, and both are asserted, using
+    your arithmetic, so the storms are provably fit for their water before your cloth lands). storm_03 is
+    deliberately the teaching rung: enough water to make a carabiner rig (1.2 kN) sweat once wind is added,
+    not enough to drown a shackle. If your mass model wants different depths, **move `peakMmPerHour`, not
+    the curve shape** — the curves carry the story (storm_03's rain arrives *with* the change at t≈30, not
+    before). Say the word and I'll re-scale.
+
+[C] 2026-07-17 — **LANE A — decision 7 helper landed, as offered: `sky.gardenExposure(bed, t)`.** The whole
+    drain term in one call — `rainAt(t) × (1 − rainShadowOver(bed))`, 0..1:
+    ```js
+    hp -= sky.gardenExposure(world.gardenBed, t) * DRAIN_PER_SEC * dt;
+    ```
+    0 = bone dry (no rain, or cloth over it); 1 = full downpour on open ground. Both terms are needed and
+    neither is enough alone. ⚠️ **It moves on its own and that's the mechanic, not a bug:** the rain shadow
+    follows the wind, so storm_02's southerly change walks the dry patch off the bed and the drain starts
+    climbing with not a single corner having failed. If that looks surprising in your HUD, please don't
+    "fix" it. Telegraph feed for the gust banner is unchanged: `wind.gustTelegraph(t)` → `{eta, dir, power}`
+    or null, and the contract still guarantees eta ≥ 1.2 s when it first appears.
+
+[C] 2026-07-17 — **Night pass done — and the reason it looked wrong is worth knowing.** storm_02 now reads
+    as an actual wild night. `sky.night` is the author's call (it was inferred from a darkness threshold),
+    but the real bug was that **darkening `scene.background` did nothing**: my cloud dome covers it at 0.85
+    opacity, so a near-white cloud texture was what you were actually looking at the whole time. The dome
+    now tints and crushes together — a lerp alone lands at #717273 because it runs in linear space and the
+    texture is baked light. It stops at 0.78 deliberately: the yard has no lights in it, and a storm you
+    can't see is a black screen (E — if a porch light or a shed lamp ever appears, I can take this darker).
+    Lightning now **lights the cloud it's inside** (#3e3e3f → #d4ddf2, the good part), and fires on the
+    biggest gusts via `sky.lightningGustPow: 10` — driven off the telegraph so the flash lands *with* the
+    gust that earned it, on top of the three authored strikes. storm_01 stays lightning-free.
+    A — the forecast card has range to sell now: `sky.night`, `rain.peakMmPerHour` (8/30/80), peak gust
+    (11/21/32 m/s) and the change time all read straight off the storm JSON.
+
+[C] 2026-07-17 — **B — decision 11 is yours to close and I'm ready either way; here's what I know.** My
+    storm_02 `downdraftOfTotal` is still **held at 0.12** with the comment in the JSON explaining it —
+    I'll delete that comment with satisfaction the moment your measurement lands. Two things that may save
+    you an afternoon:
+      · **A's anchors alone didn't fix it.** I re-measured your §7 rig `['h1','t2','p1','t1']` on the
+        *dressed* yard: still **141 m²** (h1 is house at z≈−9.9, t2 at x≈8, t1 at x≈−9 — those four span
+        the whole yard), and it dies at 0.45 (3/4, peak 6410 N). The re-point is the whole job.
+      · **A caution, not a conclusion:** sweeping the near-bed anchors I couldn't find an 18–45 m² quad
+        that *both* covers the bed ≥50% *and* survives 0.45 on a rated+shackle mix — the bed sits between
+        the house (z≈−9.9) and the posts (z≈+6), so covering it wants a biggish quad. A's a.test says ≥3
+        small quads shade the bed, so they exist and I'm likely mis-enumerating (your area calc, your
+        tension intent — I don't own either). If 0.45 turns out genuinely too hot on the real
+        bed-covering rig, the ruling's second branch is right there and **ponding now carries the
+        anti-flat burden with 3.12 kN/corner** — which is 3× the wind and cannot touch a hypar. Either
+        outcome closes it. No third sprint, as ruled.
+
+[C] 2026-07-17 — Small one, my own miss: `c.test.js` hardcoded a two-storm list while the node runner globs
+    `data/storms/`, so **storm_03 was never loaded in the browser half** — it only surfaced when my new
+    ponding case reached for `storms.storm_03_southerly` and got `undefined`. Fixed, with a note on the
+    list. If you add a storm, that list is the thing to update.

web/world/data/storms/storm_01_gentle.json

@@ -24,7 +24,9 @@
 
   "events": [],
 
-  "rain": { "curve": [[0, 0], [30, 0.15], [55, 0.2], [80, 0.08], [90, 0]] },
+  "_rain_comment": "peakMmPerHour 8 = a light shower. Mean intensity ~0.12, so at decision 10's 40x a whole storm delivers ~0.9 mm — about a millimetre of water, ~20 kg over a 25 m2 flat sail. Ponding must NOT be able to hurt anything here; that's the point of the gentle storm.",
+
+  "rain": { "peakMmPerHour": 8, "curve": [[0, 0], [30, 0.15], [55, 0.2], [80, 0.08], [90, 0]] },
 
   "sky": { "darkness": 0.15, "cloudScroll": 0.02 }
 }

web/world/data/storms/storm_02_wildnight.json

@@ -38,7 +38,11 @@
     { "t": 79, "type": "lightning", "power": 0.5 }
   ],
 
-  "rain": { "curve": [[0, 0], [10, 0.25], [35, 0.6], [55, 0.85], [70, 1.0], [90, 0.7]] },
+  "_rain_comment": "peakMmPerHour 80 = severe thunderstorm rate, the scale rainAt's 0..1 is a fraction OF. Ponding (decision 10) reads it. Mean intensity over the storm is ~0.64, and at 40x compression a 90 s storm is one hour of rain, so depth ~= 80 * 0.64 = ~51 mm = 5.1 cm on a flat sail — Lane B's measured kill: 5 cm over 25 m2 = 1250 kg = 3.1 kN/corner, against a wind load of only 0.2-1.1 kN. A flat rig should drown here. A hypar pools nothing and doesn't care.",
 
-  "sky": { "darkness": 0.8, "cloudScroll": 0.09 }
+  "rain": { "peakMmPerHour": 80, "curve": [[0, 0], [10, 0.25], [35, 0.6], [55, 0.85], [70, 1.0], [90, 0.7]] },
+
+  "_sky_comment": "night: true forces the night palette rather than leaning on the darkness threshold — it's called Wild Night and the forecast card has to sell that. lightningGustPow 10 fires a flash on any gust at/above 10 m/s of gust power (this storm's gusts top out ~12.6, so it lights up for the worst few, late, on top of the three authored strikes) — the storm's worst moments should be the ones you see.",
+
+  "sky": { "darkness": 0.94, "cloudScroll": 0.09, "night": true, "lightningGustPow": 10 }
 }

web/world/data/storms/storm_03_southerly.json

@@ -32,7 +32,9 @@
     { "t": 62, "type": "lightning", "power": 0.4 }
   ],
 
-  "rain": { "curve": [[0, 0], [28, 0.05], [34, 0.4], [55, 0.55], [80, 0.3], [90, 0.15]] },
+  "_rain_comment": "peakMmPerHour 30 = moderate. The rain arrives WITH the change at t~30 and not before — dry hot afternoon, then the southerly brings the water, which is the story the curve is telling. Mean intensity ~0.28, so at decision 10's 40x it delivers ~8 mm = 0.8 cm: ~200 kg on a 25 m2 flat sail, ~0.5 kN/corner. That is the middle rung on purpose — enough that a flat rig on carabiners (1.2 kN) should feel the water once wind is added, not enough to drown a shackle. Ponding teaches here; it kills in storm_02.",
+
+  "rain": { "peakMmPerHour": 30, "curve": [[0, 0], [28, 0.05], [34, 0.4], [55, 0.55], [80, 0.3], [90, 0.15]] },
 
   "sky": { "darkness": 0.5, "cloudScroll": 0.05 }
 }

web/world/js/skyfx.js

@@ -21,6 +21,8 @@ const clamp01 = (v) => (v < 0 ? 0 : v > 1 ? 1 : v);
 const CALM_SKY = new THREE.Color(0x9fc4e8);
 const STORM_SKY = new THREE.Color(0x2a2f3a);
 const NIGHT_SKY = new THREE.Color(0x11141c);
+const WHITE = new THREE.Color(0xffffff);
+const FLASH_COL = new THREE.Color(0xdfe8ff);
 
 // ------------------------------------------------------------ rain shadow
 /**
@@ -440,7 +442,13 @@ export function createSkyFx(o = {}) {
   const skyDef = def.sky || {};
   const darkness = skyDef.darkness ?? 0.7;
   const scroll = skyDef.cloudScroll ?? 0.06;
-  const target = (o.night ?? darkness > 0.6) ? NIGHT_SKY : STORM_SKY;
+  // The storm data gets a say: `sky.night` is the author's call, the darkness
+  // threshold is only a fallback for storms that never state one.
+  const target = (o.night ?? skyDef.night ?? darkness > 0.6) ? NIGHT_SKY : STORM_SKY;
+  // Fire a flash on any gust this strong (m/s of gust power). Storms that don't
+  // ask stay lit only by their authored strikes.
+  const lightningGustPow = skyDef.lightningGustPow ?? Infinity;
+  const firedGusts = new Set();
 
   const rain = createRain({ groundY: o.groundY ?? 0 });
   if (scene) scene.add(rain.mesh);
@@ -510,6 +518,28 @@ export function createSkyFx(o = {}) {
      */
     rainShadowOver(rect) { return shadow.fractionOver(rect); },
 
+    /**
+     * Decision 7's garden-HP drain term, 0..1, in one call — the combined helper
+     * I offered Lane A. This is the whole of "is the bed getting hit right now":
+     *
+     *     hp -= sky.gardenExposure(world.gardenBed, t) * DRAIN_PER_SEC * dt;
+     *
+     * 0 = bone dry (no rain, or the cloth is over it); 1 = full downpour on open
+     * ground. Both terms matter and neither is enough alone: a sail over the bed
+     * in a downpour is 0, and a clear sky with no sail is also 0. It uses the
+     * grid we already rebuild for the rain, so it costs a few array reads.
+     *
+     * Note it moves on its own during storm_02: the rain shadow follows the wind,
+     * so the southerly change walks the dry patch off the bed and the drain
+     * starts climbing without a single corner having failed. That's the mechanic,
+     * not a bug — worth not "fixing" if it looks surprising in the HUD.
+     */
+    gardenExposure(rect, t) {
+      const rain = wind.rainAt(t);
+      if (rain <= 0) return 0;
+      return rain * (1 - shadow.fractionOver(rect));
+    },
+
     /** Wire to the first click/keydown — browsers won't start audio otherwise. */
     unlockAudio() { audio.unlock(); },
 
@@ -539,6 +569,24 @@ export function createSkyFx(o = {}) {
           o.onEvent(ev.text);
         }
       }
+
+      // --- lightning on the biggest gusts ---
+      // The storm's worst moments should light up, not only the three authored
+      // strikes. Driven off the telegraph (which is also what the HUD banner and
+      // the audio whoosh read), so the flash lands WITH the gust that earned it.
+      // Deterministic: the gust timeline is, and each gust fires at most once.
+      const tgl = wind.gustTelegraph(t);
+      if (tgl && tgl.power >= lightningGustPow) {
+        // key on the ramp instant — stable across frames, unique per gust
+        const key = Math.round((t + tgl.eta) * 100);
+        if (!firedGusts.has(key)) {
+          firedGusts.add(key);
+          const p = Math.min(1, 0.45 + (tgl.power - lightningGustPow) * 0.06);
+          flashQueue.push({ at: t + tgl.eta, power: p });
+          flashQueue.push({ at: t + tgl.eta + 0.08 + p * 0.06, power: p * 0.5 });
+          flashQueue.push({ at: t + tgl.eta + 1.1, power: 0, thunder: p });
+        }
+      }
       for (let i = flashQueue.length - 1; i >= 0; i--) {
         if (flashQueue[i].at <= t) {
           const f = flashQueue[i];
@@ -552,7 +600,7 @@ export function createSkyFx(o = {}) {
 
       // --- sky ---
       skyCol.copy(baseSky).lerp(target, storminess * darkness);
-      if (flash > 0) skyCol.lerp(new THREE.Color(0xdfe8ff), Math.min(0.85, flash));
+      if (flash > 0) skyCol.lerp(FLASH_COL, Math.min(0.85, flash));
       if (scene) {
         if (scene.fog) {
           scene.fog.color.copy(skyCol);
@@ -565,6 +613,22 @@ export function createSkyFx(o = {}) {
 
       dome.position.copy(camPos);
       dome.material.opacity = storminess * 0.85;
+      // Tint the CLOUDS, not just the sky behind them. The dome covers the
+      // background at ~0.85 opacity, so darkening `scene.background` alone did
+      // nothing — a "wild night" still read as an overcast afternoon because the
+      // grey cloud texture was what you were actually looking at.
+      //
+      // Both a lerp AND a brightness crush: the lerp alone lands ~#717273 because
+      // it runs in linear space (84% toward night still reads mid-grey in sRGB)
+      // and the cloud texture is baked near-white. The crush is what makes night
+      // look like night. It stops at 0.78 on purpose — the yard has no lights in
+      // it yet, and a storm you can't see isn't a storm, it's a black screen.
+      const nightAmt = storminess * darkness;
+      dome.material.color.copy(WHITE)
+        .lerp(target, nightAmt * 0.92)
+        .multiplyScalar(1 - 0.78 * nightAmt);
+      // and lightning lights the cloud it's inside, which is the whole look
+      if (flash > 0) dome.material.color.lerp(FLASH_COL, Math.min(0.9, flash));
       domeTex.offset.x = (domeTex.offset.x + scroll * dt * (0.4 + speed * 0.05)) % 1;
       domeTex.offset.y = (domeTex.offset.y + scroll * dt * 0.12) % 1;
 

web/world/js/tests/c.test.js

@@ -21,7 +21,10 @@ import { createDebris } from '../debris.js';
 import { createSkyFx, RainShadow } from '../skyfx.js';
 import { weatherCases } from './weather.selftest.js';
 
-const STORMS = ['storm_01_gentle', 'storm_02_wildnight'];
+// Keep in step with data/storms/. The node runner globs the directory, so this
+// list going stale shows up here first — as it did when storm_03 landed and the
+// ponding case reached for a storm the browser half had never loaded.
+const STORMS = ['storm_01_gentle', 'storm_02_wildnight', 'storm_03_southerly'];
 
 /** @param {import('../testkit.js').Suite} t */
 export default async function run(t) {
@@ -213,6 +216,55 @@ export default async function run(t) {
     assert(half > 0.2 && half < 0.8, `a rect straddling the edge reads ${half}, want a partial`);
   });
 
+  // --- decision 7: the drain helper Lane A wires garden HP to ---
+  t.test('gardenExposure is rain AND no cover, and needs both', () => {
+    const scene = new THREE.Scene();
+    const camera = new THREE.PerspectiveCamera();
+    const wind = createWind(storms.storm_02_wildnight);
+    const sky = createSkyFx({ scene, camera, wind });
+    const bed = { x: 0, z: 0, w: 4, d: 3 };
+
+    // no sail: exposure is simply the rain
+    fixedLoop(1, FIXED_DT, (dt, time) => sky.step(dt, 70 + time, {}));
+    const open = sky.gardenExposure(bed, 70);
+    assert(Math.abs(open - wind.rainAt(70)) < 1e-9,
+      `open ground should be exposed exactly as hard as it rains: ${open} vs ${wind.rainAt(70)}`);
+    assert(open > 0.5, 'storm_02 at t=70 should be pouring');
+
+    // a panel over the bed dries it out
+    const panel = { pos: new Float32Array([-3, 3, -3, 3, 3, -3, 3, 3, 3, -3, 3, 3]), tris: [0, 1, 2, 0, 2, 3] };
+    fixedLoop(1, FIXED_DT, (dt, time) => sky.step(dt, 70 + time, { sail: panel }));
+    const covered = sky.gardenExposure(bed, 70);
+    assert(covered < open * 0.5, `cloth over the bed barely helped: ${covered.toFixed(2)} vs open ${open.toFixed(2)}`);
+
+    // and no rain means no drain, sail or not
+    assert(sky.gardenExposure(bed, 0) === 0, 'the bed is draining before the rain has started');
+    sky.dispose();
+  });
+
+  t.test('storm_02 lights up on its biggest gusts, storm_01 does not', () => {
+    const mk = (name) => {
+      const scene = new THREE.Scene();
+      const wind = createWind(storms[name]);
+      const sky = createSkyFx({ scene, camera: new THREE.PerspectiveCamera(), wind });
+      let flashes = 0, peak = 0;
+      let was = 0;
+      fixedLoop(wind.duration, FIXED_DT, (dt, time) => {
+        sky.step(dt, time, {});
+        if (sky.flash > was + 0.05) flashes++;      // a rising edge = a strike
+        was = sky.flash;
+        peak = Math.max(peak, sky.flash);
+      });
+      sky.dispose();
+      return { flashes, peak };
+    };
+    const wild = mk('storm_02_wildnight');
+    const gentle = mk('storm_01_gentle');
+    // 3 authored strikes + the worst gusts; must be more than the authored ones
+    assert(wild.flashes > 3, `wild night only flashed ${wild.flashes} times — the big gusts aren't lighting up`);
+    assert(gentle.flashes === 0, `the gentle storm flashed ${gentle.flashes} times — it has no lightning at all`);
+  });
+
   t.test('every storm in data/storms/ loads and validates', () => {
     // loadStorm throws on invalid, so reaching here with all of them is the pass
     assert(Object.keys(storms).length === STORMS.length, 'a storm failed to load');

web/world/js/tests/weather.selftest.js

@@ -11,7 +11,7 @@
 // call it with the fetched storm defs.
 
 import {
-  createWindField, validateStorm, gustEnvelope, GUST,
+  createWindField, validateStorm, gustEnvelope, GUST, RAIN_TIME_COMPRESSION,
 } from '../weather.core.js';
 
 const DT = 1 / 60;
@@ -405,6 +405,105 @@ export function weatherCases(storms) {
     assert(!validateStorm(legacy, 'legacy').ok, 'validator silently accepted the pre-SPRINT3 downdraft field');
   });
 
+  // ---- 10. the ponding story (SPRINT4 decision 10) ----
+  // Lane B owns water-on-cloth; these assert the RAIN DATA can tell the story
+  // their mass model needs, using their own arithmetic, before their cloth lands.
+  // B measured: 5 cm over a 25 m² flat sail = 1250 kg = 3.1 kN/corner, against a
+  // storm_02 wind load of only 0.2–1.1 kN. So depth is the whole mechanic.
+  const FLAT_AREA = 25;               // m², B's reference flat sail
+  const KILL_DEPTH_MM = 50;           // 5 cm — B's 3.1 kN/corner
+  /** Water on a flat sail over a whole storm, at decision 10's compression. */
+  const stormDepthMm = (def) => {
+    const f = createWindField(def);
+    return f.rainDepthMm(0, f.duration) * RAIN_TIME_COMPRESSION;
+  };
+  /** B's arithmetic: mm over an area → kN per corner (4 corners, 1000 kg/m³). */
+  const kNPerCorner = (mm) => (mm / 1000) * FLAT_AREA * 1000 * 9.81 / 4 / 1000;
+
+  test('storm_02 rain can drown a flat rig; storm_01 rain cannot', () => {
+    const wild = stormDepthMm(storms.storm_02_wildnight);
+    const gentle = stormDepthMm(storms.storm_01_gentle);
+    metrics['storm_02.pondDepth_mm'] = +wild.toFixed(1);
+    metrics['storm_02.pond_kN_per_corner'] = +kNPerCorner(wild).toFixed(2);
+    metrics['storm_01.pondDepth_mm'] = +gentle.toFixed(2);
+    metrics['storm_01.pond_kN_per_corner'] = +kNPerCorner(gentle).toFixed(3);
+
+    assert(wild >= KILL_DEPTH_MM * 0.9,
+      `storm_02 only delivers ${wild.toFixed(1)} mm — Lane B needs ~${KILL_DEPTH_MM} mm to drown a flat rig`);
+    // and it must dwarf the wind it's competing with (B: 0.2–1.1 kN/corner)
+    assert(kNPerCorner(wild) > 1.5,
+      `storm_02 ponding is only ${kNPerCorner(wild).toFixed(2)} kN/corner — no stronger than the wind`);
+    // the gentle storm must be unable to hurt anything, or the ramp is a lie
+    assert(kNPerCorner(gentle) < 0.3,
+      `storm_01 ponds ${kNPerCorner(gentle).toFixed(2)} kN/corner — a light shower must not threaten a rig`);
+    assert(wild > gentle * 20, 'the wild night should deliver vastly more water than a shower');
+  });
+
+  test('storm_03 ponding sits between the other two', () => {
+    const mid = stormDepthMm(storms.storm_03_southerly);
+    const wild = stormDepthMm(storms.storm_02_wildnight);
+    const gentle = stormDepthMm(storms.storm_01_gentle);
+    metrics['storm_03.pondDepth_mm'] = +mid.toFixed(1);
+    metrics['storm_03.pond_kN_per_corner'] = +kNPerCorner(mid).toFixed(2);
+    assert(mid > gentle * 3 && mid < wild * 0.5,
+      `storm_03 delivers ${mid.toFixed(1)} mm — wanted a real middle rung between ${gentle.toFixed(1)} and ${wild.toFixed(1)}`);
+    // it should threaten a carabiner (1.2 kN) once wind is added, not a shackle (3.2)
+    assert(kNPerCorner(mid) > 0.25 && kNPerCorner(mid) < 1.2,
+      `storm_03 ponds ${kNPerCorner(mid).toFixed(2)} kN/corner — should tease a cheap rig, not drown a decent one`);
+  });
+
+  test('rain depth integrates monotonically and matches its curve', () => {
+    const f = createWindField(storms.storm_02_wildnight);
+    // depth only ever accumulates
+    let prev = 0;
+    for (let t = 1; t <= f.duration; t += 1) {
+      const d = f.rainDepthMm(0, t);
+      assert(d >= prev - 1e-9, `rain depth went BACKWARDS at t=${t}: ${d} < ${prev}`);
+      prev = d;
+    }
+    // splitting the interval must give the same water (no double-count, no gap)
+    const whole = f.rainDepthMm(0, 90);
+    const split = f.rainDepthMm(0, 30) + f.rainDepthMm(30, 60) + f.rainDepthMm(60, 90);
+    assert(Math.abs(whole - split) < 0.05,
+      `depth(0,90)=${whole.toFixed(3)} but the three thirds sum to ${split.toFixed(3)}`);
+    // dead calm before the rain starts
+    assert(f.rainDepthMm(0, 0) === 0, 'zero-length interval delivered water');
+    assert(f.rainDepthMm(10, 5) === 0, 'a backwards interval delivered water');
+  });
+
+  test('rainMmPerHour tracks rainAt against the storm scale', () => {
+    for (const [name, def] of defs) {
+      if (!def.rain || !def.rain.curve) continue;
+      const f = createWindField(def);
+      const peak = def.rain.peakMmPerHour;
+      assert(Number.isFinite(peak), `${name} has a rain curve but no peakMmPerHour`);
+      for (let t = 0; t <= f.duration; t += 2.5) {
+        const want = f.rainAt(t) * peak;
+        assert(Math.abs(f.rainMmPerHour(t) - want) < 1e-9,
+          `${name}: rainMmPerHour ${f.rainMmPerHour(t)} != rainAt×peak ${want} at t=${t}`);
+      }
+      // rainAt stays a 0..1 intensity — skyfx uses it for drop count and opacity
+      for (let t = 0; t <= f.duration; t += 2.5) {
+        const r = f.rainAt(t);
+        assert(r >= 0 && r <= 1, `${name}: rainAt ${r} outside 0..1 at t=${t}`);
+      }
+    }
+  });
+
+  test('validator rejects a rain curve with no scale, and a silly scale', () => {
+    const noScale = JSON.parse(JSON.stringify(storms.storm_02_wildnight));
+    delete noScale.rain.peakMmPerHour;
+    assert(!validateStorm(noScale, 'x').ok, 'validator accepted a rain curve with no mm/hr scale — ponding would silently use the default');
+    for (const mm of [-1, 5000, NaN]) {
+      const d = JSON.parse(JSON.stringify(storms.storm_02_wildnight));
+      d.rain.peakMmPerHour = mm;
+      assert(!validateStorm(d, 'x').ok, `validator accepted peakMmPerHour=${mm}`);
+    }
+    const hot = JSON.parse(JSON.stringify(storms.storm_02_wildnight));
+    hot.rain.curve = [[0, 0], [45, 3], [90, 0]];
+    assert(!validateStorm(hot, 'x').ok, 'validator accepted rain intensity above 1 — the scale is peakMmPerHour, not the curve');
+  });
+
   return { cases, metrics };
 }
 

web/world/js/weather.core.js

@@ -132,6 +132,25 @@ function sampleAngleCurve(curve, t) {
 // Prototype: pow = 12 + rand*16 + 10*p, next = t + 5 + rand*7. Same shape, from JSON.
 export const DEFAULT_DOWNDRAFT = 0.22;
 
+/** Fallback rain scale, mm/hr at rainAt()==1. Storms should state their own. */
+export const DEFAULT_PEAK_MM_PER_HOUR = 40;
+
+/**
+ * SPRINT4 decision 10 — the time-compression fiat, in ONE place.
+ *
+ * Game rain accumulates ~40× real time. A 90 s storm is canonically a whole
+ * night (storm_02 telegraphs its change "around the hour mark"), so it should
+ * deliver a night's water: 90 s × 40 = 3600 s = one hour of rain. At storm_02's
+ * 80 mm/hr peak that lands ~5 cm on a flat sail — exactly Lane B's measured kill
+ * threshold (5 cm over 25 m² = 1250 kg = 3.1 kN/corner) against a wind load of
+ * only 0.2–1.1 kN. Ponding is 3–15× everything else, and it cannot pincer §7
+ * because a hypar has no flat to pool in.
+ *
+ * Exported so Lane B applies it cloth-side rather than either of us hardcoding
+ * 40 twice: how hard it rains is Lane C, how much water a sail holds is Lane B.
+ */
+export const RAIN_TIME_COMPRESSION = 40;
+
 export function buildGustTimeline(def, seed) {
   const g = def.gusts || {};
   const rng = mulberry32(seed >>> 0);
@@ -378,6 +397,45 @@ export function createWindField(def, opts = {}) {
       if (r.curve) return Math.min(1, Math.max(0, sampleCurve(r.curve, t)));
       return Math.min(1, Math.max(0, r.intensity ?? 0));
     },
+
+    /**
+     * Rain rate in REAL-WORLD mm/hr. Same curve as rainAt(), with physical units
+     * on it — `rainAt` stays 0..1 because it drives drop count and opacity, and a
+     * renderer doesn't want millimetres.
+     *
+     * This exists for ponding (decision 10). Without it Lane B has to invent the
+     * mm/hr scale to turn intensity into water mass, which is exactly the
+     * "default-off code tuned by a constant I invented" they rightly reverted.
+     * The scale is storm data, so it lives here: `rain.peakMmPerHour`.
+     * For reference: 8 = light shower, 30 = moderate, 50 = heavy, 80+ = severe.
+     */
+    rainMmPerHour(t) {
+      const r = def.rain;
+      if (!r) return 0;
+      return field.rainAt(t) * (r.peakMmPerHour ?? DEFAULT_PEAK_MM_PER_HOUR);
+    },
+
+    /**
+     * Real-world water depth in mm delivered over (t0, t1]. Deterministic
+     * trapezoid over the curve — no compression applied.
+     *
+     * Lane B multiplies by RAIN_TIME_COMPRESSION cloth-side: how much water a
+     * SAIL holds is theirs, how hard it rains is mine. Handy shape for a HUD
+     * "water delivered" readout too.
+     */
+    rainDepthMm(t0, t1, stepS = 0.25) {
+      if (!(t1 > t0)) return 0;
+      let mm = 0;
+      const n = Math.max(1, Math.ceil((t1 - t0) / stepS));
+      const h = (t1 - t0) / n;
+      let prev = field.rainMmPerHour(t0);
+      for (let i = 1; i <= n; i++) {
+        const cur = field.rainMmPerHour(t0 + i * h);
+        mm += (prev + cur) * 0.5 * h / 3600;   // mm/hr × seconds → mm
+        prev = cur;
+      }
+      return mm;
+    },
   };
 
   return field;
@@ -446,6 +504,21 @@ export function validateStorm(def, name = 'storm') {
   }
 
   if (def.rain && def.rain.curve && !isCurve(def.rain.curve)) bad('rain.curve must be [[t,intensity],...]');
+  if (def.rain) {
+    if (def.rain.curve && isCurve(def.rain.curve)
+        && def.rain.curve.some((p) => p[1] < 0 || p[1] > 1)) {
+      bad('rain.curve intensity must be 0..1 — the physical scale is rain.peakMmPerHour');
+    }
+    const mm = def.rain.peakMmPerHour;
+    if (mm != null && (!Number.isFinite(mm) || mm < 0 || mm > 300)) {
+      bad(`rain.peakMmPerHour must be 0..300 mm/hr (8 light, 30 moderate, 50 heavy, 80+ severe) — got ${mm}`);
+    }
+    // Ponding reads this; a storm that rains with no scale silently ponds at the
+    // default instead of what its author meant.
+    if (def.rain.curve && mm == null) {
+      bad('rain.curve without rain.peakMmPerHour — ponding needs the mm/hr scale (SPRINT4 decision 10)');
+    }
+  }
 
   return { ok: errors.length === 0, errors };
 }

web/world/js/weather.js

@@ -10,9 +10,9 @@
 // determinism rule can't be broken by accident.
 
 import * as THREE from '../vendor/three.module.js';
-import { createWindField, validateStorm, GUST } from './weather.core.js';
+import { createWindField, validateStorm, GUST, RAIN_TIME_COMPRESSION } from './weather.core.js';
 
-export { GUST, validateStorm };
+export { GUST, validateStorm, RAIN_TIME_COMPRESSION };
 
 // Resolved against this module, not the server root: server.py serves the repo
 // root (so the 2D prototype stays reachable), but the demo bench serves web/.
@@ -84,9 +84,16 @@ export function createWind(def, opts = {}) {
     /** Storm events fired in (a,b] — poll with (t-dt, t). Deterministic. */
     eventsBetween(a, b) { return field.eventsBetween(a, b); },
 
-    /** 0..1 rain intensity. */
+    /** 0..1 rain intensity — drives drop count and opacity. */
     rainAt(t) { return field.rainAt(t); },
 
+    /** Rain rate in real-world mm/hr. Ponding (decision 10) reads this. */
+    rainMmPerHour(t) { return field.rainMmPerHour(t); },
+
+    /** Real-world mm of water delivered over (t0,t1]. Multiply by
+     *  RAIN_TIME_COMPRESSION cloth-side — see weather.core. */
+    rainDepthMm(t0, t1) { return field.rainDepthMm(t0, t1); },
+
     /** Direction (radians, XZ plane from +X toward +Z) ignoring local effects. */
     dirAt(t) { return field.dirAt(t); },