diff --git a/src/dev.ts b/src/dev.ts
index 07fe2a0..f82f9f7 100644
--- a/src/dev.ts
+++ b/src/dev.ts
@@ -7,6 +7,7 @@ import { type Fuel, newHeatSource, setKnob, heatStep, envStep, newOutdoorEnv, ad
 import { newRoastSession, roastStep, roastResult } from './sim/roasting';
 import { Rng } from './core/rng';
 import { newGrillSession, bankCoals, placeFood, grillStep, grillResult, bedCeiling } from './sim/charcoal';
+import { newPanSession, setPanKnob, addButter, addFood, flip, baste, panStep, panResult, butterState } from './sim/pan';
 
 /**
  * Dev harness. The game is driven by mouse gestures over a 3D scene, which makes
@@ -515,6 +516,103 @@ export function installDevHarness(app: App, game: Game): void {
       return { fuel, wind, sheltered, mean: +mean.toFixed(3), stdev: +stdev.toFixed(4) };
     },
 
+    // ---- M17 + M-H4: the pan. Butter state timeline, the flip, the baste,
+    //      and the fuel differences (gas foams faster, induction never flares). ----
+
+    /** Butter state timeline at a given heat: seconds to foaming / noisette /
+     *  burnt, and the foaming-window duration (shorter at higher heat). */
+    panButter(fuel = 'gas', heat = 7, dt = 1 / 60) {
+      const s = newPanSession(fuel);
+      setPanKnob(s, heat);
+      addButter(s);
+      const mark: Record<string, number> = {};
+      let prev = butterState(s);
+      for (let i = 0; i < 60 * 60; i++) {
+        panStep(s, dt);
+        const st = butterState(s);
+        if (st !== prev) {
+          if (!(st in mark)) mark[st] = +s.seconds.toFixed(2);
+          prev = st;
+        }
+        if (st === 'burnt') break;
+      }
+      const foamWindow = mark.noisette && mark.foaming ? +(mark.noisette - mark.foaming).toFixed(2) : null;
+      return { fuel, heat, toFoaming: mark.foaming ?? null, toNoisette: mark.noisette ?? null, toBurnt: mark.burnt ?? null, foamWindow };
+    },
+
+    /** M17: cook a mushroom, flip at `flipAt`s. A well-timed flip → both sides
+     *  within 0.1; never flipping → one side burnt, one raw. */
+    panFlip(fuel = 'gas', flipAt = 9, total = 18, heat = 7) {
+      const s = newPanSession(fuel);
+      setPanKnob(s, heat);
+      addButter(s);
+      // let the butter come up to foaming before the mushroom goes in
+      for (let i = 0; i < 60 * 4; i++) panStep(s, 1 / 60);
+      addFood(s, 'button_mushroom', 'A');
+      for (let sec = 0; sec < total; sec++) {
+        if (sec === flipAt) flip(s);
+        for (let i = 0; i < 60; i++) panStep(s, 1 / 60);
+      }
+      const r = panResult(s);
+      const q = (n: number) => +n.toFixed(3);
+      return { sideGap: q(r.sideGap), doneScore: q(r.doneScore), butter: r.butter, bitterness: q(r.bitterness) };
+    },
+
+    /** M17: never flip — one side should burn (>0.9), the other stay raw. */
+    panNoFlip(fuel = 'gas', total = 20, heat = 7) {
+      const s = newPanSession(fuel);
+      setPanKnob(s, heat);
+      addButter(s);
+      for (let i = 0; i < 60 * 4; i++) panStep(s, 1 / 60);
+      addFood(s, 'button_mushroom', 'A');
+      for (let i = 0; i < 60 * total; i++) panStep(s, 1 / 60);
+      const r = panResult(s);
+      return { downMean: +r.downMean.toFixed(3), upMean: +r.upMean.toFixed(3) };
+    },
+
+    /** M17: baste the up side during noisette — raises its mean, flags the bonus.
+     *  Baste with burnt butter instead → bitterness written in. */
+    panBaste(fuel = 'gas', heat = 7) {
+      // noisette baste
+      const s = newPanSession(fuel);
+      setPanKnob(s, heat); addButter(s);
+      for (let i = 0; i < 60 * 4; i++) panStep(s, 1 / 60);
+      addFood(s, 'button_mushroom', 'A');
+      for (let i = 0; i < 60 * 8; i++) panStep(s, 1 / 60); // butter into noisette
+      const upBefore = panResult(s).upMean;
+      const b1 = baste(s, 4);
+      const upAfter = panResult(s).upMean;
+      // burnt baste (separate pan, run butter to burnt)
+      const s2 = newPanSession(fuel);
+      setPanKnob(s2, 9); addButter(s2);
+      for (let i = 0; i < 60 * 20; i++) panStep(s2, 1 / 60); // burn the butter
+      addFood(s2, 'button_mushroom', 'A');
+      const b2 = baste(s2, 4);
+      return {
+        noisette: { state: b1.state, bonus: b1.bonus, upBefore: +upBefore.toFixed(3), upAfter: +upAfter.toFixed(3) },
+        burnt: { state: b2.state, bitterness: +panResult(s2).bitterness.toFixed(3) },
+      };
+    },
+
+    /** M-H4: butter reaches noisette on gas ~faster than electric at the same
+     *  knob; induction never flares (fat has zero effect on output). */
+    panFuel(heat = 7) {
+      const noisetteAt = (fuel: string) => {
+        const s = newPanSession(fuel);
+        setPanKnob(s, heat); addButter(s);
+        for (let i = 0; i < 60 * 60; i++) { panStep(s, 1 / 60); if (butterState(s) === 'noisette') return +s.seconds.toFixed(2); }
+        return null;
+      };
+      // induction flare check: cook a fatty piece, watch output — fat must not spike it
+      const ind = newPanSession('induction');
+      setPanKnob(ind, 8); ind.env.vesselFerrous = true; addButter(ind);
+      for (let i = 0; i < 60 * 3; i++) panStep(ind, 1 / 60);
+      addFood(ind, 'button_mushroom', 'A');
+      let maxOut = 0;
+      for (let i = 0; i < 60 * 15; i++) { panStep(ind, 1 / 60); maxOut = Math.max(maxOut, ind.src.output); }
+      return { noisetteGas: noisetteAt('gas'), noisetteElectric: noisetteAt('electric'), inductionMaxOut: +maxOut.toFixed(2), inductionKnob: 8 };
+    },
+
     // ---- M-H6: charcoal is a Field, not a dial. Pure-sim probes for the bed
     //      gradient, the monotonic decay, and one-bed-two-outcomes. ----
 
diff --git a/src/sim/pan.ts b/src/sim/pan.ts
new file mode 100644
index 0000000..d2391ee
--- /dev/null
+++ b/src/sim/pan.ts
@@ -0,0 +1,272 @@
+import { Field } from '../core/field';
+import { Rng } from '../core/rng';
+import { INGREDIENTS, type IngredientId } from './ingredients';
+import {
+  type HeatSource,
+  type Environment,
+  newHeatSource,
+  newIndoorEnv,
+  setKnob,
+  heatStep,
+  applyToHeatMap,
+  addSmoke,
+} from './heatsource';
+
+/**
+ * THE PAN — the toaster generalized to a continuous, modulated heat source with
+ * two things the toaster never had: BUTTER, and a second side.
+ *
+ * The pan reads a HeatSource: the knob commands a target and the pan temp
+ * (`src.output`) chases it on the fuel's lag. Gas is instant, an electric coil
+ * drags AND remembers, induction is exact. You don't cook the knob — you cook
+ * the lag, and then you cook the BUTTER:
+ *
+ *   cold → melting → FOAMING → noisette → burnt
+ *
+ * Foaming is the moment to land your food; noisette is the nutty peak (a flavour
+ * bonus); burnt is bitterness + smoke. The food has two sides, each its own sear
+ * Field — the side on the pan browns fast, the up side barely, until you FLIP it
+ * or BASTE hot butter over it. Baste with burnt butter and you paint bitterness.
+ *
+ * On a flame fuel, rendered fat can flare (spike the output); induction never
+ * flares. Pure — Field + Rng — so the harness cooks headless and reads the
+ * judge's exact numbers.
+ */
+
+export type ButterState = 'none' | 'cold' | 'melting' | 'foaming' | 'noisette' | 'burnt';
+
+const N = 32;
+/** Butter browning per second at full pan temp. */
+const BUTTER_RATE = 0.06;
+/** Pan temp (0..10) below which butter just sits cold. */
+const MELT_TEMP = 1.5;
+/** Down-side sear per second per unit of (heat × dryness × butter). */
+const SEAR_RATE = 0.085;
+/** The up side gets this fraction of the pan's heat (radiant off the pan walls). */
+const UP_FRACTION = 0.15;
+
+export interface PanFood {
+  id: string;
+  mask: Field;
+  searA: Field;
+  searB: Field;
+  dryA: number;
+  dryB: number;
+  down: 'A' | 'B';
+  /** From cooking IN or basting WITH burnt butter — the judge tastes it. */
+  bitterness: number;
+  /** Rendered fat, feeds the flame's flare. */
+  fat: number;
+  moisture: number;
+  /** The fuel-shaped heat map under the food: gas hot-spots, induction flat. */
+  panHeat: Float32Array;
+}
+
+export interface PanSession {
+  src: HeatSource;
+  env: Environment;
+  /** 0 = fresh butter .. 1 = burnt. Only meaningful once `hasButter`. */
+  butter: number;
+  hasButter: boolean;
+  food: PanFood | null;
+  seconds: number;
+  /** Fired the frame the smoke alarm trips (burnt butter, indoors). */
+  zapped: boolean;
+  rng: Rng;
+}
+
+export function newPanSession(fuel: string = 'gas', env?: Environment): PanSession {
+  return {
+    src: newHeatSource(fuel),
+    env: env ?? newIndoorEnv(),
+    butter: 0,
+    hasButter: false,
+    food: null,
+    seconds: 0,
+    zapped: false,
+    rng: new Rng(20260719),
+  };
+}
+
+export function setPanKnob(s: PanSession, k: number): void {
+  setKnob(s.src, k);
+}
+
+export function addButter(s: PanSession): void {
+  s.hasButter = true;
+  s.butter = 0;
+}
+
+export function butterState(s: PanSession): ButterState {
+  if (!s.hasButter) return 'none';
+  const b = s.butter;
+  if (b < 0.02) return s.src.output > MELT_TEMP ? 'melting' : 'cold';
+  if (b < 0.2) return 'melting';
+  if (b < 0.45) return 'foaming';
+  if (b < 0.7) return 'noisette';
+  return 'burnt';
+}
+
+function stampDisc(mask: Field): void {
+  const n = mask.n;
+  for (let y = 0; y < n; y++) {
+    for (let x = 0; x < n; x++) {
+      const u = x / (n - 1);
+      const v = y / (n - 1);
+      if (Math.hypot(u - 0.5, v - 0.5) <= 0.42) mask.data[y * n + x] = 1;
+    }
+  }
+}
+
+/** Lay a piece of food in the pan, `down` side against the heat. */
+export function addFood(s: PanSession, id: IngredientId | string, down: 'A' | 'B' = 'A'): void {
+  const mask = new Field(N);
+  stampDisc(mask);
+  const panHeat = new Float32Array(N * N);
+  applyToHeatMap(panHeat, N, s.src, new Rng(7), mask);
+  const ing = (INGREDIENTS as Record<string, { flesh?: { moisture: number } }>)[id];
+  s.food = {
+    id,
+    mask,
+    searA: new Field(N),
+    searB: new Field(N),
+    dryA: 0,
+    dryB: 0,
+    down,
+    bitterness: 0,
+    fat: 0,
+    moisture: ing?.flesh?.moisture ?? 0.4,
+    panHeat,
+  };
+}
+
+/** Turn the piece over — the up side comes down onto the heat. */
+export function flip(s: PanSession): void {
+  if (s.food) s.food.down = s.food.down === 'A' ? 'B' : 'A';
+}
+
+/**
+ * Baste: spoon hot butter over the UP face. Raises its sear toward the down
+ * side, and carries the butter's character — noisette butter is a flavour bonus,
+ * burnt butter paints bitterness. Returns the state you basted with.
+ */
+export function baste(s: PanSession, strokes = 3): { state: ButterState; bonus: boolean } {
+  const st = butterState(s);
+  const f = s.food;
+  if (!f || !s.hasButter) return { state: st, bonus: false };
+  const up = f.down === 'A' ? f.searB : f.searA;
+  const gain = st === 'burnt' ? 0.04 : st === 'noisette' || st === 'foaming' ? 0.09 : 0.05;
+  for (let stroke = 0; stroke < strokes; stroke++) {
+    for (let i = 0; i < up.data.length; i++) if (f.mask.data[i] >= 0.5) up.data[i] = Math.min(1.2, up.data[i] + gain);
+  }
+  if (st === 'burnt') f.bitterness = Math.min(1, f.bitterness + 0.12 * strokes);
+  return { state: st, bonus: st === 'noisette' };
+}
+
+export function panStep(s: PanSession, dt: number): void {
+  s.zapped = false;
+  const f = s.food;
+  const fatLoad = f ? f.fat : 0;
+  // The pan temp chases the knob on the fuel's lag; rendered fat can flare a flame.
+  heatStep(s.src, dt, s.env, fatLoad);
+  const temp = s.src.output;
+  const p = temp / 10;
+
+  // Butter browns with pan temp — the hotter the pan, the shorter the window.
+  if (s.hasButter && temp > MELT_TEMP) {
+    s.butter = Math.min(1.2, s.butter + BUTTER_RATE * p * dt);
+  }
+  const st = butterState(s);
+  // Foaming/noisette butter conducts and flavours; burnt butter drags and taints.
+  const butterFactor = st === 'foaming' || st === 'noisette' ? 1.15 : st === 'burnt' ? 0.9 : st === 'melting' ? 1.0 : 0.85;
+
+  if (f) {
+    const downSear = f.down === 'A' ? f.searA : f.searB;
+    const upSear = f.down === 'A' ? f.searB : f.searA;
+    // The down side steams its water off, then browns fast.
+    const dryCap = 0.5 + f.moisture * 2;
+    if (f.down === 'A') f.dryA = Math.min(1, f.dryA + (p * dt) / dryCap);
+    else f.dryB = Math.min(1, f.dryB + (p * dt) / dryCap);
+    const dryDown = f.down === 'A' ? f.dryA : f.dryB;
+    const md = f.mask.data;
+    const dd = downSear.data;
+    for (let i = 0; i < dd.length; i++) {
+      if (md[i] < 0.5) continue;
+      const h = f.panHeat[i] * p;
+      dd[i] = Math.min(1.2, dd[i] + SEAR_RATE * h * (0.3 + 0.7 * dryDown) * butterFactor * dt);
+    }
+    // The up side gets only the pan's radiant halo — slow, even.
+    const ud = upSear.data;
+    for (let i = 0; i < ud.length; i++) {
+      if (md[i] < 0.5) continue;
+      ud[i] = Math.min(1.2, ud[i] + SEAR_RATE * p * UP_FRACTION * dt);
+    }
+    // Fat renders off the browning down side and feeds the flare.
+    const dmean = downSear.stats(f.mask).mean;
+    if (dmean > 0.4) f.fat = Math.min(1, f.fat + 0.35 * dt);
+    else f.fat = Math.max(0, f.fat - 0.2 * dt);
+    // Cooking in burnt butter taints the food.
+    if (st === 'burnt') f.bitterness = Math.min(1, f.bitterness + 0.05 * dt);
+  }
+
+  // Burnt butter smokes — indoors it trips the alarm once.
+  if (st === 'burnt' && addSmoke(s.env, 0.5 * dt)) s.zapped = true;
+  s.seconds += dt;
+}
+
+export interface PanResult {
+  /** Per-side browning. */
+  downMean: number;
+  upMean: number;
+  downStdev: number;
+  /** |downMean - upMean| — evenness across the two sides (the flip test). */
+  sideGap: number;
+  /** Best-side / worst-side doneness in the good window (0.5..0.85). */
+  doneScore: number;
+  butter: ButterState;
+  bitterness: number;
+  flares: number;
+}
+
+/** A good sear per side lives here; past it is over, then burnt. */
+export const SEAR_LO = 0.5;
+export const SEAR_HI = 0.85;
+export const BURN_AT = 0.95;
+
+export function panResult(s: PanSession): PanResult {
+  const f = s.food;
+  if (!f) return { downMean: 0, upMean: 0, downStdev: 0, sideGap: 0, doneScore: 0, butter: butterState(s), bitterness: 0, flares: 0 };
+  const a = f.searA.stats(f.mask);
+  const b = f.searB.stats(f.mask);
+  // A and B, not down/up — the judge sees the finished piece, both faces.
+  const inWindow = (m: number) => (m >= SEAR_LO && m < BURN_AT ? 1 - Math.abs(m - 0.68) / 0.4 : m >= BURN_AT ? 0 : m / SEAR_LO * 0.5);
+  const doneScore = Math.max(0, Math.min(1, (inWindow(a.mean) + inWindow(b.mean)) / 2));
+  return {
+    downMean: (f.down === 'A' ? a : b).mean,
+    upMean: (f.down === 'A' ? b : a).mean,
+    downStdev: (f.down === 'A' ? a : b).stdev,
+    sideGap: Math.abs(a.mean - b.mean),
+    doneScore,
+    butter: butterState(s),
+    bitterness: f.bitterness,
+    flares: 0,
+  };
+}
+
+/** The live diegetic tell for the butter — never a meter. */
+export function butterWord(s: PanSession): string {
+  switch (butterState(s)) {
+    case 'none':
+      return 'dry pan';
+    case 'cold':
+      return 'cold butter, sitting there';
+    case 'melting':
+      return 'melting…';
+    case 'foaming':
+      return 'FOAMING — in it goes';
+    case 'noisette':
+      return 'nutty brown — noisette';
+    case 'burnt':
+      return 'burnt. that is a smell you chose';
+  }
+}