feat(cooking-session): regroupement d'étapes sensible aux métadonnées d'action

L'optimiseur ne mutualisait que le pré-découpage. Il regroupe maintenant
aussi les actions SETUP (préchauffage, ébullition) entre recettes, mais
seulement quand elles sont compatibles : deux préchauffages ne fusionnent
que s'ils visent la même température détectée. Deux préchauffages à des
températures différentes restent séparés, ordonnés du plus froid au plus
chaud, et la mise en place porte une note « Four requis à N températures —
enchaîner … ». Défaut optimiste : deux préchauffages sans température
détectée fusionnent quand même (supposés compatibles).

- cooking-optimizer.ts : temperatureKey (comparaison exacte, aucune
  conversion inter-représentations), isPureSetupStep / setupSignature /
  extractMergedSetup en miroir du chemin merged-prep ; comparableTemp pour
  l'ordre seul ; detectApplianceTemperatureConflicts → CookingPhaseView.notes
- cooking-session.service.ts : `temperatures` dans l'include + mapping
- packages/shared : CookingTemperatureView, kind « merged-setup »,
  CookingTaskView.temperatures, CookingPhaseNoteView, CookingPhaseView.notes
- web : temperature-label.ts extrait de StepDescription et réutilisé ;
  taskHeadline gère merged-setup ; phaseNoteText ; bandeau .cooking-phase__note
- i18n : cookingSession.task.mergedSetupLabel, cookingSession.note.*
- tests : 7 cas Mocha « setup pooling » + test DB cooking-session,
  cas Cypress mode layout + scénario Gherkin

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/src/lib/recipe-matching/cooking-optimizer.ts

@@ -1,10 +1,12 @@
 import type {
   CookingBackgroundTaskView,
   CookingPhaseKind,
+  CookingPhaseNoteView,
   CookingPhaseView,
   CookingSessionRecipeRef,
   CookingTaskIngredientView,
   CookingTaskView,
+  CookingTemperatureView,
   TechStepView,
   UtensilView,
 } from "@batch-cooking/shared";
@@ -23,12 +25,22 @@ import type {
  * `aggregateShoppingList`, so the whole optimization is unit-testable
  * without a Postgres round-trip.
  *
- * v1 scope (see the plan / spec): preparation is the only thing *merged*
- * across recipes — a `chop`/`peel`/… technique applied to the same
- * ingredient by two or more recipes, in a step that does nothing but prep,
- * collapses into a single {@link CookingTaskView} of `kind: "merged-prep"`.
- * Cooking steps themselves are never merged (no "same oven, same
- * temperature" reasoning yet); they're only *reordered* for parallelism.
+ * Two families of work are *merged* across recipes:
+ * - **Preparation** — a `chop`/`peel`/… technique applied to the same
+ *   ingredient by two or more recipes, in a step that does nothing but
+ *   prep, collapses into one {@link CookingTaskView} of `kind:
+ *   "merged-prep"`.
+ * - **Setup** — the same `preheat`/`boil`/`bainMarie` action shared across
+ *   recipes collapses into one `kind: "merged-setup"` task, but *only when
+ *   the action metadata is compatible*: two recipes that both preheat the
+ *   oven merge only when they preheat it to the **same temperature**.
+ *   Two preheats at different temperatures stay separate (you cannot heat
+ *   one oven to two temperatures at once), are ordered coolest-first, and
+ *   the mise-en-place phase carries a {@link CookingPhaseNoteView} telling
+ *   the cook to run them in sequence.
+ *
+ * Cooking steps themselves are still never merged (no shared-oven bake
+ * batching yet); they're only *reordered* for parallelism.
  */
 
 /**
@@ -66,7 +78,8 @@ const PREP_TECHNIQUES: ReadonlySet<string> = new Set([
  *
  * - `"SETUP"` — a short active trigger, then it looks after itself: preheat
  *   the oven, bring a pot of water to the boil. Pooled into the first
- *   ("mise en place") phase so it's running before it's needed.
+ *   ("mise en place") phase so it's running before it's needed, and merged
+ *   across recipes when compatible (see {@link extractMergedSetup}).
  * - `"PASSIVE"` — unattended once started (simmer, braise, bake, marinate,
  *   rest…). Scheduled, then floated into every following phase's
  *   `background` until the step that consumes it comes up.
@@ -106,6 +119,13 @@ interface OptimizerTechStepInput {
   order: number;
   ingredients: CookingTaskIngredientView[];
   utensils: UtensilView[];
+  /**
+   * Target temperature(s) named in this same clause (`preheat` → "à 180 °C").
+   * The structured subset only — see {@link CookingTemperatureView}. Not
+   * scaled (a temperature doesn't grow with the portion count). `[]` when
+   * the clause named no temperature.
+   */
+  temperatures: CookingTemperatureView[];
 }
 
 /** One recipe step, as handed to {@link optimizeCookingPlan}. */
@@ -152,7 +172,7 @@ function scaleOf(recipe: OptimizerRecipeInput): number {
   return recipe.portions / recipe.recipePortions;
 }
 
-/** A step normalized for scheduling — techniques scaled, attention resolved, ingredients/utensils unioned across its technique clauses. */
+/** A step normalized for scheduling — techniques scaled, attention resolved, ingredients/utensils/temperatures unioned across its technique clauses. */
 interface NormalizedStep {
   /** Stable within one response: `step:<recipeIndex>:<stepId>` (the index disambiguates the same recipe planned twice). */
   taskId: string;
@@ -164,10 +184,14 @@ interface NormalizedStep {
   techSteps: OptimizerTechStepInput[];
   attention: Attention;
   isPurePrep: boolean;
+  /** Every technique in the step is a {@link SETUP_TECHNIQUES} one — eligible to pool via {@link extractMergedSetup}. */
+  isPureSetup: boolean;
   dominantTechnique: TechStepView | null;
   ingredients: CookingTaskIngredientView[];
   utensils: UtensilView[];
-  /** Set once merged-prep extraction absorbs this step wholesale (all its prep pooled elsewhere) — it then produces no standalone task. */
+  /** Distinct target temperatures across the step's clauses (see {@link unionTemperatures}) — drives setup pooling and the coolest-first ordering. */
+  temperatures: CookingTemperatureView[];
+  /** Set once merged-prep/merged-setup extraction absorbs this step wholesale — it then produces no standalone task. */
   absorbed: boolean;
 }
 
@@ -215,11 +239,62 @@ function unionUtensils(utensils: UtensilView[]): UtensilView[] {
   return [...byId.values()].sort((a, b) => a.key.localeCompare(b.key));
 }
 
+/**
+ * A stable canonical string for one temperature — `c<°C>` / `g<gasMark>` /
+ * `q<level>`, or `""` when every field is null (shouldn't happen — the
+ * upstream extractor guarantees one non-null — but stays total). Two
+ * temperatures are "the same" iff their keys are equal: **no conversion**
+ * between °C, gas marks and qualitative levels is guessed for a merge
+ * decision (same "don't invent a conversion" stance as `ShoppingListItemView`
+ * on units). °C is rounded to the nearest degree so `180` and `180.00`
+ * (a `Decimal` artefact) collapse.
+ */
+function temperatureKey(temperature: CookingTemperatureView): string {
+  if (temperature.celsius !== null) return `c${Math.round(temperature.celsius)}`;
+  if (temperature.gasMark !== null) return `g${temperature.gasMark}`;
+  if (temperature.qualitative !== null) return `q${temperature.qualitative}`;
+  return "";
+}
+
+/** Unions temperatures by {@link temperatureKey}, keeping a stable order by that key. */
+function unionTemperatures(temperatures: CookingTemperatureView[]): CookingTemperatureView[] {
+  const byKey = new Map<string, CookingTemperatureView>();
+  for (const temperature of temperatures) byKey.set(temperatureKey(temperature), temperature);
+  return [...byKey.entries()].sort(([a], [b]) => a.localeCompare(b)).map(([, value]) => value);
+}
+
+/**
+ * A single number to *order* temperatures by (coolest first) — **never** used
+ * to decide a merge (that's {@link temperatureKey}, exact-match only). Gas
+ * marks map via the French `th × 30 ≈ °C` convention and qualitative levels
+ * via rough midpoints, purely so a mixed list still sorts sensibly; a
+ * temperature-less task sorts first.
+ */
+function comparableTemp(temperature: CookingTemperatureView): number {
+  if (temperature.celsius !== null) return temperature.celsius;
+  if (temperature.gasMark !== null) return temperature.gasMark * 30;
+  if (temperature.qualitative !== null) {
+    return { low: 120, medium: 180, high: 240 }[temperature.qualitative];
+  }
+  return Number.NEGATIVE_INFINITY;
+}
+
+/** A setup task's sort position (coolest first) — its lowest target, or "before everything" when it has no detected temperature. */
+function setupTaskTemp(task: CookingTaskView): number {
+  if (task.temperatures.length === 0) return Number.NEGATIVE_INFINITY;
+  return Math.min(...task.temperatures.map(comparableTemp));
+}
+
 /** A step is pure prep only if it has techniques and every one of them is in {@link PREP_TECHNIQUES}. */
 function isPurePrepStep(techSteps: OptimizerTechStepInput[]): boolean {
   return techSteps.length > 0 && techSteps.every((ts) => PREP_TECHNIQUES.has(ts.techStep.key));
 }
 
+/** A step is pure setup only if it has techniques and every one is in {@link SETUP_TECHNIQUES} — mirror of {@link isPurePrepStep}. */
+function isPureSetupStep(techSteps: OptimizerTechStepInput[]): boolean {
+  return techSteps.length > 0 && techSteps.every((ts) => SETUP_TECHNIQUES.has(ts.techStep.key));
+}
+
 /** Resolves a step's {@link Attention} — SETUP wins, then a *trailing* passive technique, else ACTIVE (see {@link SETUP_TECHNIQUES}). */
 function attentionOf(techSteps: OptimizerTechStepInput[]): Attention {
   if (techSteps.some((ts) => SETUP_TECHNIQUES.has(ts.techStep.key))) return "SETUP";
@@ -251,6 +326,9 @@ function normalizeRecipe(recipe: OptimizerRecipeInput, recipeIndex: number): Nor
             unit: line.unit,
           })),
           utensils: ts.utensils,
+          // Temperatures are not scaled — an oven set to 180 °C for 4
+          // portions is still 180 °C for 8.
+          temperatures: ts.temperatures,
         }));
 
       const lastTech = techSteps[techSteps.length - 1];
@@ -264,9 +342,11 @@ function normalizeRecipe(recipe: OptimizerRecipeInput, recipeIndex: number): Nor
         techSteps,
         attention: attentionOf(techSteps),
         isPurePrep: isPurePrepStep(techSteps),
+        isPureSetup: isPureSetupStep(techSteps),
         dominantTechnique: lastTech ? lastTech.techStep : null,
         ingredients: unionIngredients(techSteps.flatMap((ts) => ts.ingredients)),
         utensils: unionUtensils(techSteps.flatMap((ts) => ts.utensils)),
+        temperatures: unionTemperatures(techSteps.flatMap((ts) => ts.temperatures)),
         absorbed: false,
       } satisfies NormalizedStep;
     });
@@ -283,6 +363,26 @@ function prepSignature(step: NormalizedStep): string {
   return [...new Set(pairs)].sort().join("+");
 }
 
+/**
+ * The setup signature of a pure-setup step — `<sorted technique keys>|<sorted
+ * temperature keys>`. Two steps with the same signature start the *same*
+ * appliance in the *same* state and can be pooled. The temperature part is
+ * `""` when no temperature was detected, which is a valid signature: two
+ * bare "préchauffer le four" steps then share it and merge (the optimistic
+ * default — an unknown temperature is assumed compatible). The appliance
+ * itself is deliberately not in the key (a `preheat` is the oven either
+ * way); its utensils are still unioned onto the pooled task.
+ */
+function setupSignature(step: NormalizedStep): string {
+  const techKeys = [...new Set(step.techSteps.map((ts) => ts.techStep.key))].sort().join("+");
+  const tempKeys = step.temperatures
+    .map(temperatureKey)
+    .filter((key) => key !== "")
+    .sort()
+    .join("+");
+  return `${techKeys}|${tempKeys}`;
+}
+
 /** Builds one {@link CookingTaskView} from a normalized step run as written. */
 function stepToTask(step: NormalizedStep): CookingTaskView {
   return {
@@ -292,6 +392,10 @@ function stepToTask(step: NormalizedStep): CookingTaskView {
     description: step.description,
     ingredients: step.ingredients,
     utensils: step.utensils,
+    // Only a setup step (preheat/boil/…) carries a target temperature the
+    // plan should reason about; every other step leaves it `[]` even if its
+    // text happens to mention degrees.
+    temperatures: step.attention === "SETUP" ? step.temperatures : [],
     sourceRecipes: [step.recipe],
     originalSteps: [
       {
@@ -376,6 +480,7 @@ function extractMergedPrep(steps: NormalizedStep[]): CookingTaskView[] {
       description: null,
       ingredients,
       utensils,
+      temperatures: [],
       sourceRecipes,
       originalSteps,
     });
@@ -384,6 +489,99 @@ function extractMergedPrep(steps: NormalizedStep[]): CookingTaskView[] {
   return merged.sort((a, b) => a.id.localeCompare(b.id));
 }
 
+/**
+ * Pools pure-setup steps with the same {@link setupSignature} (same action,
+ * same detected temperature) across two or more distinct recipes into one
+ * `merged-setup` {@link CookingTaskView}, marking each contributing step
+ * `absorbed`. Two `preheat` steps at *different* temperatures have different
+ * signatures and are therefore never pooled — {@link detectApplianceTemperatureConflicts}
+ * turns that into a phase note. A signature only one recipe needs is left
+ * untouched (still lands in mise-en-place as its own step task).
+ *
+ * Returns the merged tasks sorted by id.
+ */
+function extractMergedSetup(steps: NormalizedStep[]): CookingTaskView[] {
+  const bySignature = new Map<string, NormalizedStep[]>();
+  for (const step of steps) {
+    if (!step.isPureSetup) continue;
+    const signature = setupSignature(step);
+    const group = bySignature.get(signature);
+    if (group) group.push(step);
+    else bySignature.set(signature, [step]);
+  }
+
+  const merged: CookingTaskView[] = [];
+  for (const group of bySignature.values()) {
+    const recipeIndexes = new Set(group.map((s) => s.recipeIndex));
+    if (recipeIndexes.size < 2) continue;
+
+    for (const step of group) step.absorbed = true;
+
+    const firstTech = group[0]?.techSteps[0]?.techStep ?? null;
+    const ingredients = unionIngredients(
+      group.flatMap((s) => s.techSteps.flatMap((ts) => ts.ingredients)),
+    );
+    const utensils = unionUtensils(group.flatMap((s) => s.utensils));
+    const temperatures = unionTemperatures(group.flatMap((s) => s.temperatures)).sort(
+      (a, b) => comparableTemp(a) - comparableTemp(b),
+    );
+
+    // Distinct source recipes / original step texts, in input order.
+    const sourceRecipes: CookingSessionRecipeRef[] = [];
+    const seenRecipe = new Set<number>();
+    const originalSteps: CookingTaskView["originalSteps"] = [];
+    for (const step of [...group].sort((a, b) => a.recipeIndex - b.recipeIndex)) {
+      if (!seenRecipe.has(step.recipeIndex)) {
+        seenRecipe.add(step.recipeIndex);
+        sourceRecipes.push(step.recipe);
+      }
+      originalSteps.push({
+        recipeId: step.recipe.recipeId,
+        recipeName: step.recipe.name,
+        description: step.description,
+      });
+    }
+
+    const tempKey = temperatures.map(temperatureKey).join("+");
+    merged.push({
+      id: `setup:${firstTech ? firstTech.key : "setup"}:${tempKey || "any"}`,
+      kind: "merged-setup",
+      technique: firstTech,
+      description: null,
+      ingredients,
+      utensils,
+      temperatures,
+      sourceRecipes,
+      originalSteps,
+    });
+  }
+
+  return merged.sort((a, b) => a.id.localeCompare(b.id));
+}
+
+/**
+ * The kitchen has one oven: if the mise-en-place ends up with two or more
+ * `preheat` tasks at *distinct known* temperatures, they cannot run at once.
+ * Emits a single {@link CookingPhaseNoteView} listing those temperatures
+ * coolest-first so the web layer can say "enchaîner 180 °C puis 210 °C".
+ * A `preheat` with no detected temperature contributes nothing to the note
+ * (it merged optimistically with the other unknowns and we've no number to
+ * show).
+ */
+function detectApplianceTemperatureConflicts(
+  setupTasks: CookingTaskView[],
+): CookingPhaseNoteView[] {
+  const preheats = setupTasks.filter((task) => task.technique?.key === "preheat");
+  const distinct = unionTemperatures(preheats.flatMap((task) => task.temperatures))
+    .filter((temperature) => temperatureKey(temperature) !== "")
+    .sort((a, b) => comparableTemp(a) - comparableTemp(b));
+
+  const technique = preheats.find((task) => task.technique !== null)?.technique;
+  if (distinct.length < 2 || !technique) return [];
+
+  return [{ kind: "appliance-temperature-conflict", technique, temperatures: distinct }];
+}
+
 /** Maps the input recipe list to its display legend, de-duplicating an exact `(recipeId, portions)` repeat. */
 function toRecipeLegend(recipes: OptimizerRecipeInput[]): CookingSessionRecipeRef[] {
   const seen = new Set<string>();
@@ -406,9 +604,11 @@ function cookingPhaseKind(tasks: CookingTaskView[]): CookingPhaseKind {
  * See the file header. Given the week's planned recipes (already resolved
  * to reference views), returns the display legend plus the ordered phases:
  *
- * 1. **Mise en place** (`"mise-en-place"`) — every `merged-prep` task, then
- *    every leftover pure-prep step, then every `SETUP` step. Omitted
- *    entirely if it would be empty.
+ * 1. **Mise en place** (`"mise-en-place"`) — all prep first (`merged-prep`
+ *    tasks, then leftover pure-prep steps), then all setup (`merged-setup`
+ *    tasks and leftover `SETUP` steps, ordered coolest-first). Carries an
+ *    `appliance-temperature-conflict` note when the week needs the oven at
+ *    two or more temperatures. Omitted entirely if it would be empty.
  * 2. **Cooking** (`"cooking"` / `"finishing"`) — the recipes interleaved:
  *    each phase pops the next remaining step of every recipe that still has
  *    one (passive-cook steps first, so long cooks start early). A passive
@@ -420,21 +620,41 @@ export function optimizeCookingPlan(recipes: OptimizerRecipeInput[]): OptimizeCo
   const normalized = recipes.map((recipe, index) => normalizeRecipe(recipe, index));
   const allSteps = normalized.flat();
 
+  // Merged-prep first, then merged-setup — each marks its contributing
+  // steps `absorbed`, so the leftover loop below only sees the solo ones.
   const mergedPrep = extractMergedPrep(allSteps);
+  const mergedSetup = extractMergedSetup(allSteps);
 
   const phases: CookingPhaseView[] = [];
 
-  // Phase 0 — mise en place.
-  const miseTasks: CookingTaskView[] = [...mergedPrep];
+  // Phase 0 — mise en place: all prep, then all setup. Keeping the two
+  // groups apart (rather than input order) lets the setup group be ordered
+  // coolest-first without disturbing the prep order.
+  const prepTasks: CookingTaskView[] = [...mergedPrep];
+  const setupTasks: CookingTaskView[] = [...mergedSetup];
   for (const step of allSteps) {
     if (step.absorbed) continue;
-    if (step.isPurePrep || step.attention === "SETUP") {
-      miseTasks.push(stepToTask(step));
+    if (step.isPurePrep) {
+      prepTasks.push(stepToTask(step));
       step.absorbed = true; // consumed here, not again in the cooking loop
+    } else if (step.attention === "SETUP") {
+      setupTasks.push(stepToTask(step));
+      step.absorbed = true;
     }
   }
+  // Coolest oven first, so a temperature conflict reads "180 °C puis 210 °C";
+  // `id` as a stable tiebreaker keeps the plan deterministic.
+  setupTasks.sort((a, b) => setupTaskTemp(a) - setupTaskTemp(b) || a.id.localeCompare(b.id));
+
+  const miseTasks = [...prepTasks, ...setupTasks];
   if (miseTasks.length > 0) {
-    phases.push({ index: 0, kind: "mise-en-place", tasks: miseTasks, background: [] });
+    phases.push({
+      index: 0,
+      kind: "mise-en-place",
+      tasks: miseTasks,
+      background: [],
+      notes: detectApplianceTemperatureConflicts(setupTasks),
+    });
   }
 
   // Cooking phases — one "next step of each recipe" per phase. `hold` keeps
@@ -490,6 +710,9 @@ export function optimizeCookingPlan(recipes: OptimizerRecipeInput[]): OptimizeCo
       kind: cookingPhaseKind(tasks),
       tasks,
       background,
+      // Temperature conflicts only matter in mise-en-place, where all the
+      // preheats live; a cooking phase never carries a note today.
+      notes: [],
     });
 
     for (const step of phaseSteps) {

apps/api/src/modules/cooking-session/cooking-session.service.ts

@@ -47,6 +47,7 @@ function cookingSessionPlanningInclude() {
                       },
                     },
                     utensils: { include: { utensil: true } },
+                    temperatures: true,
                   },
                 },
               },
@@ -87,6 +88,19 @@ function toOptimizerRecipe(item: PlanningItemWithSteps): OptimizerRecipeInput {
         order: techStep.order,
         ingredients,
         utensils: techStep.utensils.map(({ utensil }) => ({ id: utensil.id, key: utensil.key })),
+        // Structured value only — `Decimal` °C → plain number, `qualitative`
+        // re-narrowed to the literal union (same posture as
+        // `recipe.service.ts`'s `toStepTechStepViews`).
+        temperatures: techStep.temperatures.map((temperature) => ({
+          celsius: temperature.celsius === null ? null : Number(temperature.celsius),
+          gasMark: temperature.gasMark,
+          qualitative:
+            temperature.qualitative === "low" ||
+            temperature.qualitative === "medium" ||
+            temperature.qualitative === "high"
+              ? temperature.qualitative
+              : null,
+        })),
       };
     }),
   }));

apps/api/test/cooking-session.test.ts

@@ -210,5 +210,120 @@ describe("Cooking session", () => {
       const backgrounds = later.flatMap((p: { background: unknown[] }) => p.background);
       expect(backgrounds.length).to.be.greaterThan(0);
     });
+
+    it("pools two preheats at the same temperature, and flags a conflict at different temperatures", async () => {
+      const agent = request.agent(app);
+      await agent.post("/auth/signup").send(buildSignupPayload());
+      const houseRes = await agent.post("/house").send({ name: "Chez moi" });
+      const houseId: number = houseRes.body.id;
+      const authorId: number = houseRes.body.adminId;
+
+      const preheatId = await techStepId("preheat");
+      const bakeId = await techStepId("bake");
+
+      /** A recipe whose first step is "préchauffer le four" carrying a °C temperature, then a bake. */
+      async function makeOvenRecipe(name: string, description: string, celsius: number) {
+        return prisma.recipe.create({
+          data: {
+            name,
+            authorId,
+            portions: 4,
+            steps: {
+              create: [
+                {
+                  order: 0,
+                  description,
+                  techSteps: {
+                    create: [
+                      {
+                        techStepId: preheatId,
+                        order: 0,
+                        temperatures: {
+                          create: [
+                            {
+                              start: 0,
+                              end: description.length,
+                              celsius,
+                              gasMark: null,
+                              qualitative: null,
+                              raw: `${celsius}°C`,
+                            },
+                          ],
+                        },
+                      },
+                    ],
+                  },
+                },
+                {
+                  order: 1,
+                  description: "Enfourner",
+                  techSteps: { create: [{ techStepId: bakeId, order: 0 }] },
+                },
+              ],
+            },
+          },
+        });
+      }
+
+      async function planWeek(recipeIds: number[]) {
+        const planning = await prisma.planning.create({
+          data: {
+            houseId,
+            startDate: TEST_REFERENCE_DATE.minus({ days: 2 }).toJSDate(),
+            finishDate: TEST_REFERENCE_DATE.plus({ days: 2 }).toJSDate(),
+          },
+        });
+        await prisma.planningItem.createMany({
+          data: recipeIds.map((recipeId, i) => ({
+            planningId: planning.id,
+            weekDay: i === 0 ? "lundi" : "mardi",
+            meal: i === 0 ? "dejeuner" : "diner",
+            recipeId,
+            portions: 4,
+          })),
+        });
+      }
+
+      // Same temperature → one pooled merged-setup task, no conflict note.
+      const gratin = await makeOvenRecipe("Gratin", "Préchauffer le four à 180°C", 180);
+      const tarte = await makeOvenRecipe("Tarte", "Préchauffer à 180 degrés", 180);
+      await planWeek([gratin.id, tarte.id]);
+
+      let res = await agent.get("/cooking-session").query({ date: today() });
+      expect(res.status).to.equal(200);
+      let mise = res.body.phases[0];
+      const setupMerges = mise.tasks.filter((t: { kind: string }) => t.kind === "merged-setup");
+      expect(setupMerges).to.have.length(1);
+      expect(setupMerges[0].technique.key).to.equal("preheat");
+      expect(setupMerges[0].temperatures).to.deep.equal([
+        { celsius: 180, gasMark: null, qualitative: null },
+      ]);
+      expect(mise.notes).to.deep.equal([]);
+
+      // Re-plan the same week with a second temperature → not merged, conflict note.
+      await prisma.planning.deleteMany({ where: { houseId } });
+      const roti = await makeOvenRecipe("Rôti", "Préchauffer le four à 210°C", 210);
+      await planWeek([gratin.id, roti.id]);
+
+      res = await agent.get("/cooking-session").query({ date: today() });
+      mise = res.body.phases[0];
+      expect(mise.tasks.filter((t: { kind: string }) => t.kind === "merged-setup")).to.have.length(
+        0,
+      );
+      const preheats = mise.tasks.filter(
+        (t: { technique: { key: string } | null }) => t.technique?.key === "preheat",
+      );
+      expect(preheats.map((t: { description: string }) => t.description)).to.deep.equal([
+        "Préchauffer le four à 180°C",
+        "Préchauffer le four à 210°C",
+      ]);
+      const note = mise.notes.find(
+        (n: { kind: string }) => n.kind === "appliance-temperature-conflict",
+      );
+      expect(note, "a conflict note").to.not.equal(undefined);
+      expect(note.temperatures.map((tp: { celsius: number }) => tp.celsius)).to.deep.equal([
+        180, 210,
+      ]);
+    });
   });
 });

apps/api/test/recipe-matching/cooking-optimizer.test.ts

@@ -2,6 +2,7 @@ import type {
   CookingPhaseView,
   CookingTaskIngredientView,
   CookingTaskView,
+  CookingTemperatureView,
   IngredientView,
   TechStepView,
   UnitView,
@@ -84,13 +85,19 @@ describe("cooking-optimizer", () => {
     return { id, key };
   }
 
+  /** Minimal `CookingTemperatureView` — a plain °C target, the common `preheat` case. */
+  function celsius(value: number): CookingTemperatureView {
+    return { celsius: value, gasMark: null, qualitative: null };
+  }
+
   /** One technique clause of a step. */
   function clause(
     techKey: string,
     ingredients: CookingTaskIngredientView[] = [],
     utensils: { id: number; key: string }[] = [],
+    temperatures: CookingTemperatureView[] = [],
   ): OptimizerTechStepInput {
-    return { techStep: tech(techKey), order: 0, ingredients, utensils };
+    return { techStep: tech(techKey), order: 0, ingredients, utensils, temperatures };
   }
 
   /** A step described by an ordered list of technique clauses. */
@@ -134,8 +141,9 @@ describe("cooking-optimizer", () => {
   const allTasks = (plan: { phases: CookingPhaseView[] }): CookingTaskView[] =>
     plan.phases.flatMap((phase) => phase.tasks);
 
+  /** Every pooled task — `merged-prep` and `merged-setup` alike (i.e. anything that isn't a plain recipe `step`). */
   const mergedTasks = (plan: { phases: CookingPhaseView[] }): CookingTaskView[] =>
-    allTasks(plan).filter((task) => task.kind === "merged-prep");
+    allTasks(plan).filter((task) => task.kind !== "step");
 
   const stepTasks = (plan: { phases: CookingPhaseView[] }): CookingTaskView[] =>
     allTasks(plan).filter((task) => task.kind === "step");
@@ -575,6 +583,165 @@ describe("cooking-optimizer", () => {
     });
   });
 
+  // =====================================================================
+  //  Setup pooling (preheat / boil), gated on action metadata
+  // =====================================================================
+  describe("setup pooling", () => {
+    const setupMerges = (plan: { phases: CookingPhaseView[] }) =>
+      mergedTasks(plan).filter((t) => t.kind === "merged-setup");
+    const conflictNote = (plan: { phases: CookingPhaseView[] }) =>
+      plan.phases[0]?.notes.find((n) => n.kind === "appliance-temperature-conflict");
+
+    it("merges two preheats at the same temperature into one merged-setup task", () => {
+      const recipes = [
+        recipe(1, "Gratin", [
+          step(1, 0, "Préchauffer le four à 180°C", [clause("preheat", [], [], [celsius(180)])]),
+          simpleStep(2, 1, "Enfourner", "bake"),
+        ]),
+        recipe(2, "Tarte", [
+          step(3, 0, "Préchauffer à 180 degrés", [clause("preheat", [], [], [celsius(180)])]),
+          simpleStep(4, 1, "Cuire", "bake"),
+        ]),
+      ];
+      const plan = optimizeCookingPlan(recipes);
+
+      const merged = setupMerges(plan);
+      expect(merged).to.have.lengthOf(1);
+      expect(merged[0]?.technique?.key).to.equal("preheat");
+      expect(merged[0]?.description).to.equal(null);
+      expect(merged[0]?.temperatures).to.deep.equal([celsius(180)]);
+      expect(merged[0]?.sourceRecipes.map((r) => r.recipeId)).to.have.members([1, 2]);
+      expect(merged[0]?.id).to.equal("setup:preheat:c180");
+      expect(plan.phases[0]?.notes).to.deep.equal([]);
+      assertEveryStepAccountedForOnce(recipes, plan);
+    });
+
+    it("keeps two preheats at different temperatures separate, coolest-first, with a conflict note", () => {
+      const recipes = [
+        recipe(1, "Gratin", [
+          step(1, 0, "Préchauffer le four à 210°C", [clause("preheat", [], [], [celsius(210)])]),
+          simpleStep(2, 1, "Enfourner", "bake"),
+        ]),
+        recipe(2, "Tarte", [
+          step(3, 0, "Préchauffer le four à 180°C", [clause("preheat", [], [], [celsius(180)])]),
+          simpleStep(4, 1, "Cuire", "bake"),
+        ]),
+      ];
+      const plan = optimizeCookingPlan(recipes);
+
+      expect(setupMerges(plan)).to.have.lengthOf(0);
+      const preheats = (plan.phases[0]?.tasks ?? []).filter((t) => t.technique?.key === "preheat");
+      expect(preheats.map((t) => t.description)).to.deep.equal([
+        "Préchauffer le four à 180°C",
+        "Préchauffer le four à 210°C",
+      ]);
+
+      const note = conflictNote(plan);
+      expect(note, "a conflict note on the mise-en-place phase").to.not.equal(undefined);
+      expect(note?.technique.key).to.equal("preheat");
+      expect(note?.temperatures.map((tp) => tp.celsius)).to.deep.equal([180, 210]);
+      assertEveryStepAccountedForOnce(recipes, plan);
+    });
+
+    it("merges two preheats with no detected temperature (optimistic default), no note", () => {
+      const recipes = [
+        recipe(1, "A", [
+          simpleStep(1, 0, "Préchauffer le four", "preheat"),
+          simpleStep(2, 1, "Enfourner", "bake"),
+        ]),
+        recipe(2, "B", [
+          simpleStep(3, 0, "Préchauffer le four", "preheat"),
+          simpleStep(4, 1, "Cuire", "bake"),
+        ]),
+      ];
+      const plan = optimizeCookingPlan(recipes);
+
+      const merged = setupMerges(plan);
+      expect(merged).to.have.lengthOf(1);
+      expect(merged[0]?.temperatures).to.deep.equal([]);
+      expect(merged[0]?.id).to.equal("setup:preheat:any");
+      expect(plan.phases[0]?.notes).to.deep.equal([]);
+      assertEveryStepAccountedForOnce(recipes, plan);
+    });
+
+    it("does not fire a conflict note when a known-temperature preheat sits next to an unknown one", () => {
+      const recipes = [
+        recipe(1, "A", [
+          step(1, 0, "Préchauffer le four à 200°C", [clause("preheat", [], [], [celsius(200)])]),
+          simpleStep(2, 1, "Enfourner", "bake"),
+        ]),
+        recipe(2, "B", [
+          simpleStep(3, 0, "Préchauffer le four", "preheat"),
+          simpleStep(4, 1, "Cuire", "bake"),
+        ]),
+      ];
+      const plan = optimizeCookingPlan(recipes);
+      // Two distinct signatures (`c200` vs `""`) → no merge, but only one
+      // *known* temperature → nothing to sequence, so no note.
+      expect(setupMerges(plan)).to.have.lengthOf(0);
+      expect(plan.phases[0]?.notes).to.deep.equal([]);
+      assertEveryStepAccountedForOnce(recipes, plan);
+    });
+
+    it("pools 'bring water to a boil' across recipes regardless of temperature", () => {
+      const recipes = [
+        recipe(1, "Pâtes", [
+          simpleStep(1, 0, "Porter une casserole d'eau à ébullition", "boil"),
+          simpleStep(2, 1, "Cuire les pâtes", "cook"),
+        ]),
+        recipe(2, "Riz", [
+          simpleStep(3, 0, "Porter de l'eau à ébullition", "boil"),
+          simpleStep(4, 1, "Cuire le riz", "cook"),
+        ]),
+      ];
+      const plan = optimizeCookingPlan(recipes);
+
+      const merged = setupMerges(plan);
+      expect(merged).to.have.lengthOf(1);
+      expect(merged[0]?.technique?.key).to.equal("boil");
+      expect(merged[0]?.sourceRecipes.map((r) => r.recipeId)).to.have.members([1, 2]);
+      assertEveryStepAccountedForOnce(recipes, plan);
+    });
+
+    it("keeps a preheat only one recipe needs as its own step task, no note", () => {
+      const recipes = [
+        recipe(1, "Gratin", [
+          step(1, 0, "Préchauffer le four à 200°C", [clause("preheat", [], [], [celsius(200)])]),
+          simpleStep(2, 1, "Enfourner", "bake"),
+        ]),
+        recipe(2, "Salade", [simpleStep(3, 0, "Mélanger", "mix")]),
+      ];
+      const plan = optimizeCookingPlan(recipes);
+
+      expect(setupMerges(plan)).to.have.lengthOf(0);
+      const preheat = allTasks(plan).find((t) => t.technique?.key === "preheat");
+      expect(preheat?.kind).to.equal("step");
+      expect(plan.phases[0]?.tasks).to.include(preheat);
+      expect(plan.phases[0]?.notes).to.deep.equal([]);
+      assertEveryStepAccountedForOnce(recipes, plan);
+    });
+
+    it("is deterministic with temperature-gated setup merges", () => {
+      const build = () => [
+        recipe(1, "A", [
+          step(1, 0, "Préchauffer à 180°C", [clause("preheat", [], [], [celsius(180)])]),
+          simpleStep(2, 1, "Cuire", "bake"),
+        ]),
+        recipe(2, "B", [
+          step(3, 0, "Préchauffer à 220°C", [clause("preheat", [], [], [celsius(220)])]),
+          simpleStep(4, 1, "Cuire", "bake"),
+        ]),
+        recipe(3, "C", [
+          step(5, 0, "Préchauffer à 180°C", [clause("preheat", [], [], [celsius(180)])]),
+          simpleStep(6, 1, "Cuire", "bake"),
+        ]),
+      ];
+      expect(JSON.stringify(optimizeCookingPlan(build()))).to.equal(
+        JSON.stringify(optimizeCookingPlan(build())),
+      );
+    });
+  });
+
   // =====================================================================
   //  Quantity scaling
   // =====================================================================
@@ -764,7 +931,7 @@ describe("cooking-optimizer", () => {
           simpleStep(24, 4, "Parsemer de persil", "plate", [line(ING.parsley, null, null)]),
         ]),
         recipe(104, "Poulet rôti & pommes de terre", [
-          simpleStep(30, 0, "Préchauffer le four à 210°C", "preheat"),
+          step(30, 0, "Préchauffer le four à 210°C", [clause("preheat", [], [], [celsius(210)])]),
           simpleStep(31, 1, "Éplucher les pommes de terre", "peel", [
             line(ING.potato, 1, KILOGRAM),
           ]),
@@ -774,7 +941,7 @@ describe("cooking-optimizer", () => {
           simpleStep(35, 5, "Découper et dresser", "plate"),
         ]),
         recipe(105, "Gratin dauphinois", [
-          simpleStep(40, 0, "Préchauffer le four à 180°C", "preheat"),
+          step(40, 0, "Préchauffer le four à 180°C", [clause("preheat", [], [], [celsius(180)])]),
           simpleStep(41, 1, "Éplucher les pommes de terre", "peel", [
             line(ING.potato, 1, KILOGRAM),
           ]),
@@ -837,14 +1004,25 @@ describe("cooking-optimizer", () => {
       expect(onionPool?.technique?.key).to.equal("chop");
     });
 
-    it("pulls every 'préchauffer le four' into the mise-en-place phase", () => {
+    it("keeps the two 'préchauffer le four' steps separate (different °C), coolest-first, with a conflict note", () => {
       const week = householdWeek();
       const plan = optimizeCookingPlan(week);
       const startsWithPreheat = (d: string | null) => (d ?? "").startsWith("Préchauffer le four");
+
+      // Recipes 104 (210 °C) and 105 (180 °C) preheat the same oven to
+      // different temperatures — never merged, both in mise-en-place, and
+      // ordered so the cook heats to 180 first then 210.
       const miseDescr = plan.phases[0]?.tasks.map((t) => t.description) ?? [];
-      expect(miseDescr.filter(startsWithPreheat)).to.have.lengthOf(2);
+      expect(miseDescr.filter(startsWithPreheat)).to.deep.equal([
+        "Préchauffer le four à 180°C",
+        "Préchauffer le four à 210°C",
+      ]);
       const laterDescr = plan.phases.slice(1).flatMap((p) => p.tasks.map((t) => t.description));
       expect(laterDescr.some(startsWithPreheat)).to.equal(false);
+
+      const note = plan.phases[0]?.notes.find((n) => n.kind === "appliance-temperature-conflict");
+      expect(note?.technique.key).to.equal("preheat");
+      expect(note?.temperatures.map((tp) => tp.celsius)).to.deep.equal([180, 210]);
     });
 
     it("runs the long cooks in the background of later phases (bourguignon braise, poulet rôti, gratins)", () => {

apps/web/cypress/e2e/cooking-session-page.cy.ts

@@ -44,6 +44,7 @@ function planFixture() {
         index: 0,
         kind: "mise-en-place",
         background: [],
+        notes: [],
         tasks: [
           {
             id: "prep:chop:onion",
@@ -58,6 +59,7 @@ function planFixture() {
               },
             ],
             utensils: [{ id: 1, key: "knife" }],
+            temperatures: [],
             sourceRecipes: [
               { recipeId: 1, name: "Soupe à l'oignon", portions: 4 },
               { recipeId: 2, name: "Tarte à l'oignon", portions: 6 },
@@ -70,6 +72,7 @@ function planFixture() {
         index: 1,
         kind: "cooking",
         background: [],
+        notes: [],
         tasks: [
           {
             id: "step:0:1",
@@ -78,6 +81,7 @@ function planFixture() {
             description: "Faire mijoter le bouillon",
             ingredients: [],
             utensils: [],
+            temperatures: [],
             sourceRecipes: [{ recipeId: 1, name: "Soupe à l'oignon", portions: 4 }],
             originalSteps: [],
           },
@@ -95,6 +99,7 @@ function planFixture() {
             recipeName: "Soupe à l'oignon",
           },
         ],
+        notes: [],
         tasks: [
           {
             id: "step:1:3",
@@ -103,6 +108,7 @@ function planFixture() {
             description: "Enfourner la tarte",
             ingredients: [],
             utensils: [],
+            temperatures: [],
             sourceRecipes: [{ recipeId: 2, name: "Tarte à l'oignon", portions: 6 }],
             originalSteps: [],
           },
@@ -112,6 +118,74 @@ function planFixture() {
   };
 }
 
+/**
+ * A one-phase plan whose mise-en-place has a pooled `merged-setup` preheat
+ * (both recipes, same 180 °C) plus two un-merged preheats at 200 °C / 220 °C
+ * that trigger an `appliance-temperature-conflict` note.
+ */
+function setupPlanFixture() {
+  const soupe = { recipeId: 1, name: "Soupe", portions: 4 };
+  const gratin = { recipeId: 2, name: "Gratin", portions: 4 };
+  const roti = { recipeId: 3, name: "Rôti", portions: 4 };
+  return {
+    startDate: "2026-08-17T00:00:00.000Z",
+    finishDate: "2026-08-23T00:00:00.000Z",
+    recipes: [soupe, gratin, roti],
+    phases: [
+      {
+        index: 0,
+        kind: "mise-en-place",
+        background: [],
+        notes: [
+          {
+            kind: "appliance-temperature-conflict",
+            technique: { id: 9, key: "preheat" },
+            temperatures: [
+              { celsius: 200, gasMark: null, qualitative: null },
+              { celsius: 220, gasMark: null, qualitative: null },
+            ],
+          },
+        ],
+        tasks: [
+          {
+            id: "setup:preheat:c180",
+            kind: "merged-setup",
+            technique: { id: 9, key: "preheat" },
+            description: null,
+            ingredients: [],
+            utensils: [],
+            temperatures: [{ celsius: 180, gasMark: null, qualitative: null }],
+            sourceRecipes: [soupe, gratin],
+            originalSteps: [],
+          },
+          {
+            id: "step:1:10",
+            kind: "step",
+            technique: { id: 9, key: "preheat" },
+            description: "Préchauffer le four à 200°C",
+            ingredients: [],
+            utensils: [],
+            temperatures: [{ celsius: 200, gasMark: null, qualitative: null }],
+            sourceRecipes: [gratin],
+            originalSteps: [],
+          },
+          {
+            id: "step:2:20",
+            kind: "step",
+            technique: { id: 9, key: "preheat" },
+            description: "Préchauffer le four à 220°C",
+            ingredients: [],
+            utensils: [],
+            temperatures: [{ celsius: 220, gasMark: null, qualitative: null }],
+            sourceRecipes: [roti],
+            originalSteps: [],
+          },
+        ],
+      },
+    ],
+  };
+}
+
 describe("Cooking session page", () => {
   beforeEach(() => {
     cy.viewport(1400, 900);
@@ -226,6 +300,27 @@ describe("Cooking session page", () => {
     cy.get(".cooking-stepper").should("not.exist");
   });
 
+  it("renders a merged-setup preheat with its temperature and the oven-conflict note", () => {
+    cy.intercept("GET", /\/cooking-session\?/, { statusCode: 200, body: setupPlanFixture() });
+    cy.visit("/cuisiner?date=2026-08-17");
+
+    // The pooled preheat shows the technique label + its pooled temperature,
+    // flagged shared like a merged-prep task.
+    cy.get(".cooking-task--merged-setup")
+      .should("contain.text", "180 °C")
+      .and("contain.text", "Mutualisé");
+
+    // The phase warns the oven is needed at two more temperatures, in order.
+    cy.get(".cooking-phase__note")
+      .should("contain.text", "2 températures")
+      .and("contain.text", "200 °C puis 220 °C");
+
+    // The two un-merged preheats are still listed as their own tasks.
+    cy.contains(".cooking-task", "Préchauffer le four à 200°C").should("be.visible");
+    cy.contains(".cooking-task", "Préchauffer le four à 220°C").should("be.visible");
+    cy.contains(".cooking-plan__count", "0 / 3 tâches").should("be.visible");
+  });
+
   it("shows an error state when the request fails", () => {
     cy.intercept("GET", /\/cooking-session\?/, {
       statusCode: 500,

apps/web/cypress/e2e/cooking-session.feature

@@ -53,3 +53,11 @@ Feature: Start cooking an optimized plan
     Then I should see "Soupe à l'oignon"
     And the recipe "Soupe à l'oignon" should link to "/recettes/1"
     And the recipe "Tarte à l'oignon" should link to "/recettes/2"
+
+  Scenario: Two recipes preheat the oven to different temperatures
+    Given the planning for this week has recipes "Gratin" and "Rôti"
+    And the cooking plan for "2026-08-17" needs the oven at 180 °C and 210 °C
+    When I visit "/cuisiner?date=2026-08-17"
+    Then I should see the oven conflict note "enchaîner 180 °C puis 210 °C"
+    And I should see "Préchauffer le four à 180°C"
+    And I should see "Préchauffer le four à 210°C"

apps/web/cypress/e2e/cooking-session.ts

@@ -59,6 +59,7 @@ Given(
             index: 0,
             kind: "mise-en-place",
             background: [],
+            notes: [],
             tasks: [
               {
                 id: "prep:chop:onion",
@@ -73,6 +74,7 @@ Given(
                   },
                 ],
                 utensils: [],
+                temperatures: [],
                 sourceRecipes: [
                   { recipeId: 1, name: "Soupe à l'oignon", portions: 4 },
                   { recipeId: 2, name: "Tarte à l'oignon", portions: 4 },
@@ -117,6 +119,7 @@ Given("the cooking plan for {string} has a mise en place then a cooking step", (
           index: 0,
           kind: "mise-en-place",
           background: [],
+          notes: [],
           tasks: [
             {
               id: "prep:chop:onion",
@@ -131,6 +134,7 @@ Given("the cooking plan for {string} has a mise en place then a cooking step", (
                 },
               ],
               utensils: [],
+              temperatures: [],
               sourceRecipes: [
                 { recipeId: 1, name: "Soupe à l'oignon", portions: 4 },
                 { recipeId: 2, name: "Tarte à l'oignon", portions: 6 },
@@ -143,6 +147,7 @@ Given("the cooking plan for {string} has a mise en place then a cooking step", (
           index: 1,
           kind: "cooking",
           background: [],
+          notes: [],
           tasks: [
             {
               id: "step:0:1",
@@ -151,6 +156,7 @@ Given("the cooking plan for {string} has a mise en place then a cooking step", (
               description: "Faire mijoter le bouillon",
               ingredients: [],
               utensils: [],
+              temperatures: [],
               sourceRecipes: [{ recipeId: 1, name: "Soupe à l'oignon", portions: 4 }],
               originalSteps: [],
             },
@@ -161,6 +167,51 @@ Given("the cooking plan for {string} has a mise en place then a cooking step", (
   });
 });
 
+Given("the cooking plan for {string} needs the oven at 180 °C and 210 °C", (date: string) => {
+  const celsius = (value: number) => ({ celsius: value, gasMark: null, qualitative: null });
+  const preheatStep = (id: string, recipe: { recipeId: number; name: string }, value: number) => ({
+    id,
+    kind: "step",
+    technique: { id: 9, key: "preheat" },
+    description: `Préchauffer le four à ${value}°C`,
+    ingredients: [],
+    utensils: [],
+    temperatures: [celsius(value)],
+    sourceRecipes: [recipe],
+    originalSteps: [],
+  });
+  const gratin = { recipeId: 1, name: "Gratin", portions: 4 };
+  const roti = { recipeId: 2, name: "Rôti", portions: 4 };
+  cy.intercept("GET", `**/cooking-session?date=${date}`, {
+    statusCode: 200,
+    body: {
+      startDate: `${date}T00:00:00.000Z`,
+      finishDate: "2026-08-23T00:00:00.000Z",
+      recipes: [gratin, roti],
+      phases: [
+        {
+          index: 0,
+          kind: "mise-en-place",
+          background: [],
+          notes: [
+            {
+              kind: "appliance-temperature-conflict",
+              technique: { id: 9, key: "preheat" },
+              temperatures: [celsius(180), celsius(210)],
+            },
+          ],
+          // Coolest first, as the optimizer emits them.
+          tasks: [preheatStep("step:0:1", gratin, 180), preheatStep("step:1:2", roti, 210)],
+        },
+      ],
+    },
+  });
+});
+
+Then("I should see the oven conflict note {string}", (text: string) => {
+  cy.get(".cooking-phase__note").should("contain.text", text);
+});
+
 When("I open the {string} cooking tab", (label: string) => {
   cy.contains(".cooking-session-page__tab", label).click();
 });

apps/web/src/features/recipes/steps/StepDescription.tsx

@@ -1,38 +1,12 @@
-import type {
-  StepTechStepTemperatureView,
-  StepTechStepView,
-  SubmitTechStepCorrectionResult,
-} from "@batch-cooking/shared";
+import type { StepTechStepView, SubmitTechStepCorrectionResult } from "@batch-cooking/shared";
 import { Fragment, useEffect, useRef, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { Tooltip } from "../../../components/ui/Tooltip";
 import { splitDescriptionSegments } from "./highlight-tech-steps";
 import { TechStepCorrectionPopover } from "./TechStepCorrectionPopover";
+import { temperatureLabel } from "./temperature-label";
 import { type TextSelectionRange, useTextSelection } from "./use-text-selection";
 
-/**
- * Human label for a detected temperature — the °C value, else the gas-mark
- * number, else the qualitative level, each via i18n. Shown in the
- * highlight's Tooltip (`raw` is what stays inline as the highlighted text).
- * `t` is passed in (see `ingredient-label.ts` for the same "plain function,
- * unit-testable" split).
- */
-function temperatureLabel(
-  temperature: StepTechStepTemperatureView,
-  t: (key: string, options?: Record<string, unknown>) => string,
-): string {
-  if (temperature.celsius !== null) {
-    return t("recipes.temperature.celsius", { value: temperature.celsius });
-  }
-  if (temperature.gasMark !== null) {
-    return t("recipes.temperature.gasMark", { value: temperature.gasMark });
-  }
-  if (temperature.qualitative !== null) {
-    return t(`recipes.temperature.qualitative.${temperature.qualitative}`);
-  }
-  return temperature.raw;
-}
-
 /**
  * A recipe step's description, with every detected technique's exact
  * matched words highlighted and given a {@link Tooltip} naming the

apps/web/src/features/recipes/steps/temperature-label.ts

@@ -0,0 +1,40 @@
+/**
+ * The three structured fields a temperature label is built from. Both
+ * `StepTechStepTemperatureView` (recipe-detail highlight — also carries a
+ * `raw` fragment) and `CookingTemperatureView` (the cooking session's
+ * pooled setup targets — no `raw`) satisfy this, so {@link temperatureLabel}
+ * serves both without either type depending on the other.
+ */
+export interface TemperatureLabelInput {
+  celsius: number | null;
+  gasMark: number | null;
+  qualitative: "low" | "medium" | "high" | null;
+  /** The exact recognized fragment, present only on a recipe-detail temperature — used only as a last-resort fallback (unreachable when one of the three above is set, which the contract guarantees). */
+  raw?: string;
+}
+
+/**
+ * Human label for a detected temperature — the °C value, else the gas-mark
+ * number, else the qualitative level, each via i18n (`recipes.temperature.*`).
+ * `t` is passed in rather than calling `useTranslation` here so this stays a
+ * plain function usable from non-component code and unit-testable without
+ * mounting i18next — same split as `ingredient-label.ts` / `shopping-list.ts`.
+ *
+ * Extracted from `StepDescription.tsx` (its original home) once the cooking
+ * session page needed the same label for a `merged-setup` task.
+ */
+export function temperatureLabel(
+  temperature: TemperatureLabelInput,
+  t: (key: string, options?: Record<string, unknown>) => string,
+): string {
+  if (temperature.celsius !== null) {
+    return t("recipes.temperature.celsius", { value: temperature.celsius });
+  }
+  if (temperature.gasMark !== null) {
+    return t("recipes.temperature.gasMark", { value: temperature.gasMark });
+  }
+  if (temperature.qualitative !== null) {
+    return t(`recipes.temperature.qualitative.${temperature.qualitative}`);
+  }
+  return temperature.raw ?? "";
+}

apps/web/src/locales/fr/translation.json

@@ -350,8 +350,13 @@
     "background": {
       "title": "Pendant ce temps"
     },
+    "note": {
+      "applianceTemperatureConflict": "Four requis à {{count}} températures — enchaîner {{sequence}}",
+      "sequenceSeparator": "puis"
+    },
     "task": {
       "mergedPrepLabel": "{{technique}} : {{items}}",
+      "mergedSetupLabel": "{{technique}} · {{temperature}}",
       "forRecipes": "pour {{recipes}}",
       "utensils": "Ustensiles",
       "sharedBadge": "Mutualisé"

apps/web/src/pages/cooking-session/CookingSessionPage.tsx

@@ -13,7 +13,13 @@ import { apiClient } from "../../api/client";
 import { CheckboxOption } from "../../components/ui/Checkbox";
 import { WeekNavigator } from "../../features/planning/WeekNavigator";
 import { cookingProgress } from "./cooking-progress";
-import { phaseProgress, reconcileChecked, taskHeadline, taskRecipeNames } from "./cooking-session";
+import {
+  phaseNoteText,
+  phaseProgress,
+  reconcileChecked,
+  taskHeadline,
+  taskRecipeNames,
+} from "./cooking-session";
 import "./cooking-session-page.scss";
 
 /** Load state for the `GET /cooking-session` call — same discriminated-union shape as `ShoppingListPage`'s own state. */
@@ -269,6 +275,12 @@ function PhaseSection({
 
   return (
     <section className={`cooking-phase cooking-phase--${phase.kind}`}>
+      {(phase.notes ?? []).map((note) => (
+        <p key={note.kind} className="cooking-phase__note">
+          {phaseNoteText(note, t)}
+        </p>
+      ))}
+
       {phase.background.length > 0 && (
         <div className="cooking-phase__background">
           <span className="cooking-phase__background-title">
@@ -299,7 +311,7 @@ function PhaseSection({
   );
 }
 
-/** A single actionable task — a merged-prep pool or a plain recipe step — with a tick to mark it done. */
+/** A single actionable task — a merged pool (prep or setup) or a plain recipe step — with a tick to mark it done. */
 function TaskCard({
   task,
   checked,
@@ -310,6 +322,7 @@ function TaskCard({
   onToggle: (isChecked: boolean) => void;
 }) {
   const { t } = useTranslation();
+  const isMerged = task.kind === "merged-prep" || task.kind === "merged-setup";
 
   return (
     <CheckboxOption
@@ -320,7 +333,7 @@ function TaskCard({
       <span className="cooking-task__body">
         <span className="cooking-task__headline">
           {taskHeadline(task, t)}
-          {task.kind === "merged-prep" && (
+          {isMerged && (
             <span className="cooking-task__badge">{t("cookingSession.task.sharedBadge")}</span>
           )}
         </span>

apps/web/src/pages/cooking-session/cooking-session-page.scss

@@ -303,6 +303,20 @@
   flex-direction: column;
   gap: var(--space-sm);
 
+  // A phase-level caveat — today only the "four requis à 2 températures"
+  // conflict. A tinted callout in the accent colour so it reads as a
+  // heads-up, not a plain paragraph.
+  &__note {
+    margin: 0;
+    padding: var(--space-sm) var(--space-md);
+    border-left: 3px solid var(--color-accent);
+    border-radius: 0 var(--radius-md) var(--radius-md) 0;
+    background: color-mix(in srgb, var(--color-accent) 10%, var(--color-surface));
+    color: var(--color-text);
+    font-size: var(--font-size-sm);
+    font-weight: 600;
+  }
+
   // "Pendant ce temps" — passive cooks still running from earlier phases.
   &__background {
     border-left: 3px solid var(--color-border);
@@ -346,7 +360,8 @@
       align-items: flex-start;
     }
 
-    .cooking-task--merged-prep {
+    .cooking-task--merged-prep,
+    .cooking-task--merged-setup {
       border-left: 3px solid var(--color-accent);
     }
 

apps/web/src/pages/cooking-session/cooking-session.ts

@@ -1,9 +1,12 @@
 import type {
+  CookingPhaseNoteView,
   CookingPhaseView,
   CookingTaskIngredientView,
   CookingTaskView,
+  CookingTemperatureView,
   OptimizedCookingPlanView,
 } from "@batch-cooking/shared";
+import { temperatureLabel } from "../../features/recipes/steps/temperature-label";
 
 /**
  * Minimal shape of `react-i18next`'s `t` — just what this module needs.
@@ -39,27 +42,66 @@ export function formatIngredientLine(line: CookingTaskIngredientView, t: Transla
   return `${amount} ${unit}${name}`.trim();
 }
 
+/**
+ * The pooled target temperature(s) of a `merged-setup` task as one string —
+ * `"180 °C"`, `"180 °C / Thermostat 6"` in the rare mixed case, or `""` when
+ * no temperature was detected. Labels via the shared {@link temperatureLabel}
+ * (same `recipes.temperature.*` keys as the recipe-step highlight).
+ */
+export function formatTemperatures(temperatures: CookingTemperatureView[], t: TranslateFn): string {
+  return temperatures.map((temperature) => temperatureLabel(temperature, t)).join(" / ");
+}
+
 /**
  * The headline shown on a task card:
  * - `merged-prep` — `"Émincer : 3 oignon, 200 g carotte"` (technique label +
  *   its pooled ingredient lines), built from the
  *   `cookingSession.task.mergedPrepLabel` template.
+ * - `merged-setup` — `"Préchauffer · 180 °C"` (technique label + pooled
+ *   temperature), via `cookingSession.task.mergedSetupLabel`; just the
+ *   technique label when no temperature was detected.
  * - `step` — the original recipe step text, verbatim.
  */
 export function taskHeadline(task: CookingTaskView, t: TranslateFn): string {
   if (task.kind === "step") return task.description ?? "";
+
   const technique = task.technique
     ? t(`catalog.techSteps.${task.technique.key}`)
     : t("cookingSession.phase.mise-en-place");
+
+  if (task.kind === "merged-setup") {
+    const temperature = formatTemperatures(task.temperatures, t);
+    return temperature
+      ? t("cookingSession.task.mergedSetupLabel", { technique, temperature })
+      : technique;
+  }
+
   const items = task.ingredients.map((line) => formatIngredientLine(line, t)).join(", ");
   return t("cookingSession.task.mergedPrepLabel", { technique, items });
 }
 
-/** Comma-joined names of the recipes a task belongs to — one for a `step`, several for a pooled `merged-prep`. */
+/** Comma-joined names of the recipes a task belongs to — one for a `step`, several for a pooled `merged-prep`/`merged-setup`. */
 export function taskRecipeNames(task: CookingTaskView): string {
   return task.sourceRecipes.map((recipe) => recipe.name).join(", ");
 }
 
+/**
+ * The sentence for a phase-level note (see {@link CookingPhaseNoteView}).
+ * Today the only kind is `appliance-temperature-conflict`: the oven is
+ * needed at several temperatures at once, so the cook runs the preheats one
+ * after another — "Four requis à 2 températures — enchaîner 180 °C puis
+ * 210 °C" (temperatures already coolest-first from the optimizer).
+ */
+export function phaseNoteText(note: CookingPhaseNoteView, t: TranslateFn): string {
+  const sequence = note.temperatures
+    .map((temperature) => temperatureLabel(temperature, t))
+    .join(` ${t("cookingSession.note.sequenceSeparator")} `);
+  return t("cookingSession.note.applianceTemperatureConflict", {
+    count: note.temperatures.length,
+    sequence,
+  });
+}
+
 /**
  * Drops any ticked id that no longer names a task in the current plan.
  * `CookingTaskView.id` is only stable *within one plan response* (see its

packages/shared/src/types/cooking-session.ts

@@ -43,6 +43,27 @@ export interface CookingTaskIngredientView {
   unit: UnitView | null;
 }
 
+/**
+ * A target temperature carried by a {@link CookingTaskView} or a
+ * {@link CookingPhaseNoteView} — the *structured* subset of
+ * `StepTechStepTemperatureView` (no `raw` text / spans / `source`), which is
+ * all the optimizer needs to decide whether two `preheat` actions can be
+ * merged and to order them coolest-first. Exactly as on the recipe-detail
+ * view, at least one of the three is non-null:
+ * - `celsius`     — °C (a °F mention was converted upstream).
+ * - `gasMark`     — a gas-mark / thermostat number.
+ * - `qualitative` — `"low" | "medium" | "high"` ("feu doux/moyen/vif").
+ *
+ * Two temperatures are treated as the *same* only when they match in the
+ * same representation — no °C↔gas-mark↔qualitative conversion is guessed
+ * for a merge decision (same stance as `ShoppingListItemView` on units).
+ */
+export interface CookingTemperatureView {
+  celsius: number | null;
+  gasMark: number | null;
+  qualitative: "low" | "medium" | "high" | null;
+}
+
 /**
  * One actionable unit of work in a phase's `tasks` list.
  *
@@ -56,19 +77,34 @@ export interface CookingTaskIngredientView {
  *   `description` is `null` (the web layer composes a label from
  *   `technique` + `ingredients`), `sourceRecipes` lists every recipe it
  *   covers, and `ingredients` holds the pooled quantity.
+ * - `kind: "merged-setup"` — the same setup action (`preheat` / `boil` /
+ *   `bainMarie`) shared across recipes: two recipes that both preheat the
+ *   oven **to the same temperature** become one task. `description` is
+ *   `null` (the web layer composes a label from `technique` +
+ *   `temperatures`), `temperatures` holds the pooled target(s). Two
+ *   `preheat` actions at *different* temperatures are never merged — they
+ *   stay separate tasks and the phase carries a
+ *   {@link CookingPhaseNoteView} telling the cook to run them in sequence.
  *
- * `id` is stable within a single response (`"prep:<techniqueKey>:<ingredientKey>"`
- * or `"step:<stepId>"`) so the frontend can key a checklist off it.
- * `originalSteps` is the provenance trail — the exact step text(s) this
- * task stands in for, so the UI can link back to "voir la recette".
+ * `temperatures` is non-empty only for a `merged-setup` task, or a
+ * `kind: "step"` task whose step is itself a setup action (so the plan can
+ * still order and conflict-check a preheat that only one recipe needs);
+ * `[]` otherwise.
+ *
+ * `id` is stable within a single response
+ * (`"prep:<techniqueKey>:<ingredientKey>"`, `"setup:<techniqueKey>:<tempKey>"`
+ * or `"step:<recipeIndex>:<stepId>"`) so the frontend can key a checklist
+ * off it. `originalSteps` is the provenance trail — the exact step text(s)
+ * this task stands in for, so the UI can link back to "voir la recette".
  */
 export interface CookingTaskView {
   id: string;
-  kind: "merged-prep" | "step";
+  kind: "merged-prep" | "merged-setup" | "step";
   technique: TechStepView | null;
   description: string | null;
   ingredients: CookingTaskIngredientView[];
   utensils: UtensilView[];
+  temperatures: CookingTemperatureView[];
   sourceRecipes: CookingSessionRecipeRef[];
   originalSteps: { recipeId: number; recipeName: string; description: string }[];
 }
@@ -89,17 +125,45 @@ export interface CookingBackgroundTaskView {
   recipeName: string;
 }
 
+/**
+ * Kind of a {@link CookingPhaseNoteView}. Only one today; kept as a named
+ * union so a future note type is an additive change and the web layer's
+ * `switch` stays exhaustive.
+ *
+ * - `"appliance-temperature-conflict"` — the week needs the same appliance
+ *   (the oven, via `preheat`) at two or more incompatible temperatures.
+ *   The conflicting tasks are left un-merged and ordered coolest-first; the
+ *   note tells the cook to run them one after the other.
+ */
+export type CookingPhaseNoteKind = "appliance-temperature-conflict";
+
+/**
+ * A caveat attached to a whole phase rather than a single task — see
+ * {@link CookingPhaseNoteKind}. `technique` is the action the conflict is
+ * about (`preheat`), `temperatures` the distinct incompatible targets in
+ * ascending order (coolest first), so the web layer can compose e.g.
+ * "Four requis à 2 températures — enchaîner 180 °C puis 210 °C".
+ */
+export interface CookingPhaseNoteView {
+  kind: CookingPhaseNoteKind;
+  technique: TechStepView;
+  temperatures: CookingTemperatureView[];
+}
+
 /**
  * One phase of the optimized plan: a batch of work the cook does now
- * (`tasks`), plus any passive cooks carried over from before (`background`).
- * `index` is 0-based and matches the array position — carried explicitly so
- * a caller rendering a single phase still knows where it sits.
+ * (`tasks`), plus any passive cooks carried over from before (`background`)
+ * and any phase-level caveats (`notes`, usually `[]` — see
+ * {@link CookingPhaseNoteView}). `index` is 0-based and matches the array
+ * position — carried explicitly so a caller rendering a single phase still
+ * knows where it sits.
  */
 export interface CookingPhaseView {
   index: number;
   kind: CookingPhaseKind;
   tasks: CookingTaskView[];
   background: CookingBackgroundTaskView[];
+  notes: CookingPhaseNoteView[];
 }
 
 /**