apps/api/prisma/migrations/20260905120000_leftovers_portions_requested/migration.sql

@@ -0,0 +1,27 @@
+-- Splits "portions to prepare" from "portions actually needed" on a
+-- planning slot, and adds the two columns a leftovers-serving item needs
+-- (its source item + how much of its own pool was thrown away). Purely
+-- additive — no existing column renamed. See the `PlanningItem` model doc
+-- comments and issue #34.
+
+-- `discarded_portions` and `source_planning_item_id` are trivial adds.
+ALTER TABLE "planning_item"
+  ADD COLUMN "discarded_portions" INTEGER NOT NULL DEFAULT 0,
+  ADD COLUMN "source_planning_item_id" INTEGER;
+
+-- `portions_requested` is NOT NULL but the table may have rows already:
+-- add it nullable, backfill, then lock it down — same discipline as the
+-- `ingredient_unit_catalog` / `planning_item_portions` migrations. Every
+-- pre-existing row predates this feature, so it had no leftovers:
+-- requested == prepared at the time it was added.
+ALTER TABLE "planning_item" ADD COLUMN "portions_requested" INTEGER;
+UPDATE "planning_item" SET "portions_requested" = "portions";
+ALTER TABLE "planning_item" ALTER COLUMN "portions_requested" SET NOT NULL;
+
+-- Self-FK for a "leftovers" item pointing back at the item it draws from.
+-- ON DELETE CASCADE: removing the source item removes everything served
+-- from its pool too (same as the Planning -> PlanningItem cascade).
+ALTER TABLE "planning_item"
+  ADD CONSTRAINT "planning_item_source_planning_item_id_fkey"
+  FOREIGN KEY ("source_planning_item_id") REFERENCES "planning_item"("id")
+  ON DELETE CASCADE ON UPDATE CASCADE;

apps/api/prisma/schema.prisma

@@ -218,12 +218,36 @@ model PlanningItem {
   weekDay    String @map("week_day")
   meal       String
   recipeId   Int    @map("recipe_id")
+  /// Portions actually *prepared* for this slot — always a whole multiple
+  /// of `recipe.portions` (a dish is cooked in whole batches). Derived from
+  /// `portionsRequested` + the recipe's yield via `computeBatchedPortions`
+  /// (`@batch-cooking/shared`) in `addPlanningItem`, never sent raw by the
+  /// client. On a "leftovers" item (`sourcePlanningItemId` set) it always
+  /// equals `portionsRequested`.
   portions   Int
+  /// How many portions this slot must actually feed. For a fresh item
+  /// (`sourcePlanningItemId` null), `<= portions` — the gap is this item's
+  /// leftover pool. For a "leftovers" item, always `== portions` (serving
+  /// leftovers prepares nothing new, so it can't generate more — no
+  /// leftovers-on-leftovers).
+  portionsRequested    Int  @map("portions_requested")
+  /// Non-null only on a "leftovers" item: the item whose leftover pool it
+  /// draws from. `onDelete: Cascade` — deleting the source item also
+  /// deletes everything served from its leftovers (same reasoning as the
+  /// existing `Planning` -> `PlanningItem` cascade).
+  sourcePlanningItemId Int? @map("source_planning_item_id")
+  /// Portions of *this* item's leftover pool explicitly thrown away (the
+  /// basket's "jeter" button). Always 0 on a "leftovers" item (its own
+  /// pool is null by construction).
+  discardedPortions    Int  @default(0) @map("discarded_portions")
   /// See `Planning.createdAt` — same admin-metrics-only timestamp.
   createdAt  DateTime @default(now()) @map("created_at")
 
   planning           Planning       @relation(fields: [planningId], references: [id], onDelete: Cascade)
   recipe             Recipe         @relation(fields: [recipeId], references: [id])
+  sourcePlanningItem PlanningItem?  @relation("PlanningItemLeftoverSource", fields: [sourcePlanningItemId], references: [id], onDelete: Cascade)
+  /// The "leftovers" items served from this item's own pool — inverse of `sourcePlanningItem`.
+  leftoverUses       PlanningItem[] @relation("PlanningItemLeftoverSource")
 
   @@map("planning_item")
 }

apps/api/src/modules/planning/planning.service.ts

@@ -2,6 +2,7 @@ import { type DateTime, getWeekStart, toDateOnly } from "@batch-cooking/date-too
 import { HttpError } from "@batch-cooking/error-tools";
 import {
   type AddPlanningItemInput,
+  computeBatchedPortions,
   ErrorCode,
   type PlanningItemView,
   type PlanningView,
@@ -69,6 +70,9 @@ export async function getPlanningForDate(
         weekDay: item.weekDay,
         meal: item.meal,
         portions: item.portions,
+        portionsRequested: item.portionsRequested,
+        discardedPortions: item.discardedPortions,
+        sourceItem: item.sourcePlanningItemId !== null ? { id: item.sourcePlanningItemId } : null,
         recipe: item.recipe,
       })),
     };
@@ -144,6 +148,18 @@ export async function addPlanningItem(
     }
     await assertRecipeVisible(input.recipeId, viewerId, viewerHouseId);
 
+    // `assertRecipeVisible` already guaranteed the recipe exists and is
+    // visible — this second read just pulls its written yield, needed to
+    // turn "portions requested" into "portions to actually prepare"
+    // (a whole number of batches, see `computeBatchedPortions`). The
+    // `?? 1` never triggers in practice (the assert above threw otherwise);
+    // it only keeps TypeScript happy about `findUnique`'s `| null`.
+    const recipe = await prisma.recipe.findUnique({
+      where: { id: input.recipeId },
+      select: { portions: true },
+    });
+    const { portions } = computeBatchedPortions(recipe?.portions ?? 1, input.portionsRequested);
+
     const weekStart = getWeekStart(toDateOnly(date));
     const planning = await findOrCreatePlanningForWeek(houseId, weekStart);
 
@@ -153,14 +169,19 @@ export async function addPlanningItem(
         weekDay: input.weekDay,
         meal: input.meal,
         recipeId: input.recipeId,
-        portions: input.portions,
+        portions,
+        portionsRequested: input.portionsRequested,
       },
       include: { recipe: { select: { id: true, name: true } } },
     });
 
     analytics.recordEvent("planning.item_added", {
       actorId: viewerId,
-      context: { recipeId: input.recipeId, portions: input.portions },
+      context: {
+        recipeId: input.recipeId,
+        portions,
+        portionsRequested: input.portionsRequested,
+      },
     });
 
     return {
@@ -168,6 +189,9 @@ export async function addPlanningItem(
       weekDay: item.weekDay,
       meal: item.meal,
       portions: item.portions,
+      portionsRequested: item.portionsRequested,
+      discardedPortions: item.discardedPortions,
+      sourceItem: item.sourcePlanningItemId !== null ? { id: item.sourcePlanningItemId } : null,
       recipe: item.recipe,
     };
   } catch (err) {

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

@@ -177,6 +177,7 @@ describe("Cooking session", () => {
             meal: "dejeuner",
             recipeId: soupe.id,
             portions: 4,
+            portionsRequested: 4,
           },
           {
             planningId: planning.id,
@@ -184,6 +185,7 @@ describe("Cooking session", () => {
             meal: "diner",
             recipeId: tarte.id,
             portions: 4,
+            portionsRequested: 4,
           },
         ],
       });
@@ -280,6 +282,7 @@ describe("Cooking session", () => {
             meal: i === 0 ? "dejeuner" : "diner",
             recipeId,
             portions: 4,
+            portionsRequested: 4,
           })),
         });
       }

apps/api/test/planning-portions.test.ts

@@ -0,0 +1,73 @@
+import { computeAvailableLeftover, computeBatchedPortions } from "@batch-cooking/shared";
+import { expect } from "chai";
+
+/**
+ * Pure portion arithmetic from `@batch-cooking/shared` — no DB, so this
+ * suite skips `resetDatabase`. The API (`addPlanningItem`, and later the
+ * leftover-assignment endpoints) and the web app both call these; the
+ * numbers below are the two worked examples from issue #34 plus the
+ * boundary cases.
+ */
+describe("planning portion arithmetic", () => {
+  describe("computeBatchedPortions", () => {
+    it("rounds up to one batch when fewer portions are requested than the recipe yields", () => {
+      expect(computeBatchedPortions(4, 3)).to.deep.equal({ portions: 4, leftover: 1 });
+    });
+
+    it("cooks several batches when more portions are requested than one batch yields", () => {
+      expect(computeBatchedPortions(4, 10)).to.deep.equal({ portions: 12, leftover: 2 });
+    });
+
+    it("leaves no leftover on an exact batch boundary", () => {
+      expect(computeBatchedPortions(4, 4)).to.deep.equal({ portions: 4, leftover: 0 });
+      expect(computeBatchedPortions(4, 8)).to.deep.equal({ portions: 8, leftover: 0 });
+    });
+
+    it("still prepares one batch when a single portion is requested", () => {
+      expect(computeBatchedPortions(6, 1)).to.deep.equal({ portions: 6, leftover: 5 });
+    });
+
+    it("handles a one-portion recipe (every request is an exact number of batches)", () => {
+      expect(computeBatchedPortions(1, 5)).to.deep.equal({ portions: 5, leftover: 0 });
+    });
+  });
+
+  describe("computeAvailableLeftover", () => {
+    const base = { portions: 12, portionsRequested: 10, discardedPortions: 0, leftoverUses: [] };
+
+    it("is the prepared-minus-requested pool when nothing has been discarded or served", () => {
+      expect(computeAvailableLeftover(base)).to.equal(2);
+    });
+
+    it("subtracts portions already served to other slots", () => {
+      expect(
+        computeAvailableLeftover({ ...base, leftoverUses: [{ portions: 1 }, { portions: 1 }] }),
+      ).to.equal(0);
+    });
+
+    it("subtracts explicitly discarded portions", () => {
+      expect(computeAvailableLeftover({ ...base, discardedPortions: 2 })).to.equal(0);
+    });
+
+    it("never goes negative", () => {
+      expect(
+        computeAvailableLeftover({
+          ...base,
+          discardedPortions: 5,
+          leftoverUses: [{ portions: 3 }],
+        }),
+      ).to.equal(0);
+    });
+
+    it("is 0 for an item whose request landed exactly on a batch (no pool at all)", () => {
+      expect(
+        computeAvailableLeftover({
+          portions: 8,
+          portionsRequested: 8,
+          discardedPortions: 0,
+          leftoverUses: [],
+        }),
+      ).to.equal(0);
+    });
+  });
+});

apps/api/test/planning.test.ts

@@ -114,6 +114,7 @@ describe("Planning", () => {
           meal: "diner",
           recipeId: recipe.id,
           portions: 4,
+          portionsRequested: 3,
         },
       });
 
@@ -122,7 +123,14 @@ describe("Planning", () => {
       expect(res.status).to.equal(200);
       expect(res.body.id).to.equal(planning.id);
       expect(res.body.items).to.have.length(1);
-      expect(res.body.items[0]).to.include({ weekDay: "lundi", meal: "diner" });
+      expect(res.body.items[0]).to.include({
+        weekDay: "lundi",
+        meal: "diner",
+        portions: 4,
+        portionsRequested: 3,
+        discardedPortions: 0,
+      });
+      expect(res.body.items[0].sourceItem).to.equal(null);
       expect(res.body.items[0].recipe).to.include({ id: recipe.id, name: "Ratatouille" });
     });
 
@@ -171,6 +179,7 @@ describe("Planning", () => {
           meal: "dejeuner",
           recipeId: recipe.id,
           portions: 2,
+          portionsRequested: 2,
         },
       });
 
@@ -183,4 +192,83 @@ describe("Planning", () => {
       expect(thisWeekRes.body).to.equal(null);
     });
   });
+
+  describe("POST /planning/items", () => {
+    /** Signs up, creates a household, and returns an authenticated agent + a saved recipe with the given yield. */
+    async function setup(recipePortions: number) {
+      const agent = request.agent(app);
+      await agent.post("/auth/signup").send(buildSignupPayload());
+      const houseRes = await agent.post("/house").send({ name: "Chez moi" });
+      const recipe = await prisma.recipe.create({
+        data: { name: "Lasagnes", authorId: houseRes.body.adminId, portions: recipePortions },
+      });
+      return { agent, recipe };
+    }
+
+    it("rounds the prepared portions up to a whole batch of the recipe and reports the leftover", async () => {
+      const { agent, recipe } = await setup(4);
+
+      const res = await agent.post("/planning/items").send({
+        date: today(),
+        weekDay: "lundi",
+        meal: "diner",
+        recipeId: recipe.id,
+        portionsRequested: 3,
+      });
+
+      expect(res.status).to.equal(201);
+      // 3 requested, 4-portion recipe -> one batch of 4 prepared, 1 leftover.
+      expect(res.body).to.include({ portions: 4, portionsRequested: 3, discardedPortions: 0 });
+      expect(res.body.sourceItem).to.equal(null);
+
+      const stored = await prisma.planningItem.findUnique({ where: { id: res.body.id } });
+      expect(stored).to.include({ portions: 4, portionsRequested: 3 });
+    });
+
+    it("cooks several batches when more portions are requested than one batch yields", async () => {
+      const { agent, recipe } = await setup(4);
+
+      const res = await agent.post("/planning/items").send({
+        date: today(),
+        weekDay: "mardi",
+        meal: "dejeuner",
+        recipeId: recipe.id,
+        portionsRequested: 10,
+      });
+
+      expect(res.status).to.equal(201);
+      // 10 requested, 4-portion recipe -> three batches (12) prepared, 2 leftover.
+      expect(res.body).to.include({ portions: 12, portionsRequested: 10 });
+    });
+
+    it("leaves no leftover when the request lands exactly on a batch boundary", async () => {
+      const { agent, recipe } = await setup(4);
+
+      const res = await agent.post("/planning/items").send({
+        date: today(),
+        weekDay: "mercredi",
+        meal: "diner",
+        recipeId: recipe.id,
+        portionsRequested: 8,
+      });
+
+      expect(res.status).to.equal(201);
+      expect(res.body).to.include({ portions: 8, portionsRequested: 8 });
+    });
+
+    it("rejects a non-positive portionsRequested with 400 VALIDATION_ERROR", async () => {
+      const { agent, recipe } = await setup(4);
+
+      const res = await agent.post("/planning/items").send({
+        date: today(),
+        weekDay: "lundi",
+        meal: "diner",
+        recipeId: recipe.id,
+        portionsRequested: 0,
+      });
+
+      expect(res.status).to.equal(400);
+      expect(res.body.code).to.equal(ErrorCode.VALIDATION_ERROR);
+    });
+  });
 });

apps/api/test/recipe.test.ts

@@ -1031,6 +1031,7 @@ describe("Recipes", () => {
           meal: "diner",
           recipeId: recipe.id,
           portions: 4,
+          portionsRequested: 4,
         },
       });
 

apps/api/test/shopping-list.test.ts

@@ -150,6 +150,7 @@ describe("Shopping list", () => {
             meal: "dejeuner",
             recipeId: recipe.id,
             portions: 4,
+            portionsRequested: 4,
           },
           {
             planningId: planning.id,
@@ -157,6 +158,7 @@ describe("Shopping list", () => {
             meal: "diner",
             recipeId: recipe.id,
             portions: 4,
+            portionsRequested: 4,
           },
         ],
       });
@@ -211,6 +213,7 @@ describe("Shopping list", () => {
             meal: "dejeuner",
             recipeId: recipeA.id,
             portions: 4,
+            portionsRequested: 4,
           },
           {
             planningId: planning.id,
@@ -218,6 +221,7 @@ describe("Shopping list", () => {
             meal: "diner",
             recipeId: recipeB.id,
             portions: 4,
+            portionsRequested: 4,
           },
         ],
       });
@@ -272,6 +276,7 @@ describe("Shopping list", () => {
             meal: "dejeuner",
             recipeId: recipeA.id,
             portions: 2,
+            portionsRequested: 2,
           },
           {
             planningId: planning.id,
@@ -279,6 +284,7 @@ describe("Shopping list", () => {
             meal: "diner",
             recipeId: recipeB.id,
             portions: 2,
+            portionsRequested: 2,
           },
         ],
       });
@@ -323,6 +329,7 @@ describe("Shopping list", () => {
           meal: "dejeuner",
           recipeId: recipe.id,
           portions: 2,
+          portionsRequested: 2,
         },
       });
 

apps/web/cypress/e2e/planning.feature

@@ -40,7 +40,7 @@ Feature: Adding a recipe to the planning
     And I select unit "unité" for the first ingredient
     And I fill in the last ingredient's quantity with "1" and unit "unité"
     And I click the button "Importer"
-    Then the planning add request should have included recipe 99, weekDay "lundi", meal "petit-dejeuner", and portions 4
+    Then the planning add request should have included recipe 99, weekDay "lundi", meal "petit-dejeuner", and requested portions 4
     And the recipe picker dialog should be closed
     And the recipe "Fish Pie" should appear in the first planning slot with 4 portions
 
@@ -54,6 +54,6 @@ Feature: Adding a recipe to the planning
     And I click the source item "Ratatouille"
     And I click the button "Confirmer"
     Then the import request for "7777" should have included the name "Ratatouille"
-    And the planning add request should have included recipe 100, weekDay "lundi", meal "petit-dejeuner", and portions 4
+    And the planning add request should have included recipe 100, weekDay "lundi", meal "petit-dejeuner", and requested portions 4
     And the recipe picker dialog should be closed
     And the recipe "Ratatouille" should appear in the first planning slot with 4 portions

apps/web/cypress/e2e/planning.ts

@@ -152,6 +152,9 @@ Given("adding recipe {int} to the planning will succeed", (recipeId: number) =>
       weekDay: "lundi",
       meal: "petit-dejeuner",
       portions: 4,
+      portionsRequested: 4,
+      discardedPortions: 0,
+      sourceItem: null,
       recipe: { id: recipeId, name: "Ratatouille" },
     },
   }).as("addPlanningItem");
@@ -250,11 +253,11 @@ When("I choose an ingredient for the unresolved line {string}", (rawText: string
 });
 
 Then(
-  "the planning add request should have included recipe {int}, weekDay {string}, meal {string}, and portions {int}",
+  "the planning add request should have included recipe {int}, weekDay {string}, meal {string}, and requested portions {int}",
-  (recipeId: number, weekDay: string, meal: string, portions: number) => {
+  (recipeId: number, weekDay: string, meal: string, portionsRequested: number) => {
     cy.wait("@addPlanningItem")
       .its("request.body")
-      .should("deep.include", { recipeId, weekDay, meal, portions });
+      .should("deep.include", { recipeId, weekDay, meal, portionsRequested });
   },
 );
 

apps/web/src/features/planning/RecipePickerDialog.tsx

@@ -1,4 +1,5 @@
 import {
+  computeBatchedPortions,
   type DietView,
   ErrorCode,
   type IngredientView,
@@ -306,7 +307,9 @@ export function RecipePickerDialog({
         weekDay: slot.weekDay,
         meal: slot.meal,
         recipeId: saved.id,
-        portions: payload.portions,
+        // A freshly imported recipe is added at exactly its own yield, so
+        // requested == prepared and there's no leftover to compute here.
+        portionsRequested: payload.portions,
       });
       onAdded(planningItem);
       onClose();
@@ -334,7 +337,7 @@ export function RecipePickerDialog({
         weekDay: slot.weekDay,
         meal: slot.meal,
         recipeId: selectedRecipe.id,
-        portions: parsedPortions,
+        portionsRequested: parsedPortions,
       });
       onAdded(item);
       onClose();
@@ -374,13 +377,22 @@ export function RecipePickerDialog({
   }
 
   if (selectedRecipe) {
+    // A whole number of batches of this recipe is what actually gets
+    // cooked; the hint below only shows when that leaves a leftover.
+    const parsedRequested = Number(portions);
+    const batched =
+      Number.isInteger(parsedRequested) && parsedRequested > 0
+        ? computeBatchedPortions(selectedRecipe.portions, parsedRequested)
+        : null;
     return (
       <Dialog
         onClose={onClose}
         title={t("planning.picker.confirmTitle", { recipe: selectedRecipe.name })}
       >
         <div className="recipe-picker-confirm">
-          <label htmlFor="planning-picker-portions">{t("planning.picker.portionsLabel")}</label>
+          <label htmlFor="planning-picker-portions">
+            {t("planning.picker.portionsRequestedLabel")}
+          </label>
           <input
             id="planning-picker-portions"
             type="number"
@@ -389,6 +401,14 @@ export function RecipePickerDialog({
             value={portions}
             onChange={(e) => setPortions(e.target.value)}
           />
+          {batched && batched.leftover > 0 && (
+            <p className="recipe-picker-confirm__batched-hint">
+              {t("planning.picker.batchedHint", {
+                prepared: batched.portions,
+                leftover: batched.leftover,
+              })}
+            </p>
+          )}
           {submitError && <p className="field-error">{submitError}</p>}
           <div className="recipe-picker-confirm__actions">
             <button type="button" onClick={() => setSelectedRecipe(null)} disabled={isSubmitting}>

apps/web/src/features/planning/recipe-picker-dialog.scss

@@ -147,6 +147,16 @@
   }
 }
 
+// "→ N portions préparées, M en restes" — shown under the portions field
+// only when the requested count doesn't land on a whole batch of the
+// recipe, so the user sees the leftover a batch-cooking round-up creates
+// before confirming (issue #34).
+.recipe-picker-confirm__batched-hint {
+  margin: 0;
+  color: var(--color-text-muted);
+  font-size: var(--font-size-sm);
+}
+
 .recipe-picker-confirm__actions {
   display: flex;
   justify-content: flex-end;

apps/web/src/features/recipes/sources/RecipeImportForm.tsx

@@ -322,7 +322,10 @@ export function RecipeImportForm({
             weekDay: planningSlot.weekDay,
             meal: planningSlot.meal,
             recipeId: saved.id,
-            portions: Number(portions),
+            // This form's `portions` field is the recipe's own yield; an
+            // import lands on the slot at exactly that, so requested ==
+            // prepared and no leftover is created.
+            portionsRequested: Number(portions),
           });
           onImported({ recipe: saved, planningItem });
           return;

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

@@ -145,7 +145,8 @@
       "loading": "Chargement des recettes…",
       "empty": "Aucune recette ne correspond à ces filtres.",
       "confirmTitle": "Ajouter {{recipe}}",
-      "portionsLabel": "Nombre de portions",
+      "portionsRequestedLabel": "Portions demandées",
+      "batchedHint": "→ {{prepared}} portions préparées, {{leftover}} en restes",
       "backButton": "Retour",
       "confirmButton": "Ajouter au planning",
       "adding": "Ajout…",

packages/shared/src/index.ts

@@ -6,6 +6,7 @@
 export * from "./data/catalog-labels-en.js";
 export * from "./data/catalog-labels-fr.js";
 export * from "./errors/error-codes.js";
+export * from "./logic/planning-portions.js";
 export * from "./schemas/account.js";
 export * from "./schemas/admin.js";
 export * from "./schemas/auth.js";

packages/shared/src/logic/planning-portions.ts

@@ -0,0 +1,68 @@
+/**
+ * Pure portion arithmetic for the planning grid — no I/O, so it runs
+ * identically in the API (deriving what to store / validating a leftover
+ * assignment) and the web app (the "→ prepared / leftover" hint under the
+ * portions field, and the leftovers basket). Colocated here in
+ * `@batch-cooking/shared` rather than in either app for exactly that
+ * "one formula, two callers" reason.
+ */
+
+/** What {@link computeBatchedPortions} returns: the portions actually prepared, and the leftover that creates. */
+export interface BatchedPortions {
+  /** Portions actually cooked — always a whole multiple of the recipe's own yield. */
+  portions: number;
+  /** `portions - requestedPortions` — how many prepared portions nobody asked for yet. */
+  leftover: number;
+}
+
+/**
+ * Splits "portions this slot must actually feed" into "portions prepared"
+ * and the leftover that creates. A dish is only ever cooked in whole
+ * batches of its own recipe (never a fraction of a plat), so the prepared
+ * count is rounded **up** to the next multiple of the recipe's yield:
+ *
+ * ```
+ * portions = ceil(requestedPortions / recipePortions) * recipePortions
+ * leftover = portions - requestedPortions
+ * ```
+ *
+ * e.g. for a 4-portion recipe: 3 requested → 4 prepared, 1 leftover;
+ * 10 requested → 12 prepared, 2 leftover; 8 requested → 8 prepared,
+ * 0 leftover.
+ *
+ * Both inputs are expected to be positive integers (a recipe always yields
+ * at least 1, `addPlanningItemSchema` rejects a non-positive request) —
+ * `Math.max(1, …)` on the batch count is just belt and braces so a stray 0
+ * still produces one batch rather than `0` prepared.
+ */
+export function computeBatchedPortions(
+  recipePortions: number,
+  requestedPortions: number,
+): BatchedPortions {
+  const batches = Math.max(1, Math.ceil(requestedPortions / recipePortions));
+  const portions = batches * recipePortions;
+  return { portions, leftover: portions - requestedPortions };
+}
+
+/**
+ * How many portions of one item's leftover pool are still available to
+ * assign to another slot: what it prepared beyond what it needed, minus
+ * whatever has since been thrown away (`discardedPortions`) or already
+ * served elsewhere (`leftoverUses`, the items that point back at this one).
+ * Never negative.
+ *
+ * Same function on both sides of the wire: the API revalidates every
+ * leftover assignment against it (from `leftoverUses` loaded by Prisma),
+ * the web basket derives each line's remaining count from it (using the
+ * flat `planning.items` array it already has in memory).
+ */
+export function computeAvailableLeftover(item: {
+  portions: number;
+  portionsRequested: number;
+  discardedPortions: number;
+  leftoverUses: { portions: number }[];
+}): number {
+  const pool = item.portions - item.portionsRequested;
+  const served = item.leftoverUses.reduce((sum, use) => sum + use.portions, 0);
+  return Math.max(0, pool - item.discardedPortions - served);
+}

packages/shared/src/schemas/planning.ts

@@ -32,8 +32,13 @@ export const addPlanningItemSchema = z.object({
   weekDay: z.enum(WEEK_DAYS),
   meal: z.enum(MEALS),
   recipeId: z.number().int().positive(),
-  /** How many portions to prepare for this slot — a plain manual entry, see `PlanningItemView.portions`. */
+  /**
-  portions: z.number().int().positive("Le nombre de portions doit être positif"),
+   * How many portions this slot must actually feed. The server derives the
+   * batched `portions` to prepare from this plus the recipe's own yield
+   * (`computeBatchedPortions`, `@batch-cooking/shared`) — the client never
+   * sends `portions` directly. See `PlanningItemView.portionsRequested`.
+   */
+  portionsRequested: z.number().int().positive("Le nombre de portions doit être positif"),
 });
 /** Inferred TS type for {@link addPlanningItemSchema}'s validated output. */
 export type AddPlanningItemInput = z.infer<typeof addPlanningItemSchema>;

packages/shared/src/types/planning.ts

@@ -37,8 +37,27 @@ export interface PlanningItemView {
   weekDay: string;
   /** Which meal of the day this item is for — see {@link Meal} (free-form for now, same reason). */
   meal: string;
-  /** How many portions to prepare for this slot — entered by whoever assigns the recipe (`addPlanningItemSchema`'s `portions`). The picker UI pre-fills this from `Recipe.portions` (see {@link RecipeSummaryView.portions}) but it's still stored independently here, since a slot may scale the recipe up/down from its written yield. */
+  /**
+   * How many portions are actually **prepared** for this slot — always a
+   * whole multiple of the recipe's own yield (`Recipe.portions`), since a
+   * dish is only ever cooked in whole batches. Derived from
+   * {@link portionsRequested} + the recipe's yield via
+   * `computeBatchedPortions`, never entered directly. For a
+   * leftovers-serving item ({@link sourceItem} set) this equals
+   * {@link portionsRequested} — serving leftovers cooks nothing new.
+   */
   portions: number;
+  /**
+   * How many portions this slot is actually meant to feed — the single
+   * number entered when adding the recipe ("on est 3", "il en faut 10").
+   * For a fresh item this is `<= portions`; the gap is this item's
+   * leftover pool.
+   */
+  portionsRequested: number;
+  /** Portions of this item's own leftover pool already explicitly thrown away (the basket's "jeter" button). Always 0 on a leftovers-serving item. */
+  discardedPortions: number;
+  /** Set only when this item serves another item's leftovers rather than a freshly cooked batch — points back at that source item. `null` for a normal item. */
+  sourceItem: { id: number } | null;
   recipe: {
     id: number;
     name: string;

specs/backend-architecture.md

@@ -226,17 +226,26 @@ Router `/planning` (`planning.routes.ts`/`.service.ts`), `requireAuth`.
   null`. `null` recouvre **deux** états normaux confondus : pas de foyer, ou
   aucun `Planning` ne couvre cette date — jamais une erreur.
 - `POST /planning/items` → `addPlanningItem`, 201. Body `addPlanningItemSchema`
-  = `{ date, weekDay, meal, recipeId, portions }` (`weekDay`/`meal` sont des
+  = `{ date, weekDay, meal, recipeId, portionsRequested }` (`weekDay`/`meal` sont
-  enums `WEEK_DAYS`/`MEALS` de `packages/shared`, réellement validés ici — pas
+  des enums `WEEK_DAYS`/`MEALS` de `packages/shared`, réellement validés ici —
-  juste une convention documentée). `recipeId` doit exister et être visible par
+  pas juste une convention documentée). `recipeId` doit exister et être visible
-  l'appelant (`assertRecipeVisible`, `recipe.service.ts`) → 404
+  par l'appelant (`assertRecipeVisible`, `recipe.service.ts`) → 404
   `RECIPE_NOT_FOUND` sinon.
 - `DELETE /planning/items/:id` → `removePlanningItem`, 204.
 
-**`PlanningItem.portions`** est saisi **indépendamment** de `Recipe.portions`
+**Portions demandées vs préparées (issue #34)** — le client n'envoie que
-(le rendement "tel qu'écrit" de la recette) — un créneau peut mettre à
+`portionsRequested` (« combien ce créneau doit nourrir »). `addPlanningItem`
-l'échelle. Le picker web pré-remplit depuis `Recipe.portions` mais envoie
+en dérive `portions` (ce qui est **réellement préparé**) via
-toujours sa propre valeur.
+`computeBatchedPortions(recipe.portions, portionsRequested)`
+(`@batch-cooking/shared`, pur) : on arrondit au multiple supérieur du
+rendement de la recette (`ceil(demandées / recette.portions) × recette.portions`)
+— on cuisine des lots entiers, jamais une fraction de plat. L'écart
+`portions − portionsRequested` est le **pool de restes** de cet item.
+`getPlanningForDate` renvoie les deux valeurs plus `discardedPortions` et
+`sourceItem` (dérivé de `sourcePlanningItemId`) dans chaque
+`PlanningItemView`, sans `include` Prisma supplémentaire. Les routes
+d'attribution/jet de restes et l'exclusion des items « restes » de la liste
+de courses / session de cuisine arrivent dans une itération ultérieure.
 
 **Création de la semaine** — `findOrCreatePlanningForWeek` est le seul
 endroit qui crée une ligne `Planning`, retrouvée par `startDate` exact (un

specs/batch-cooking-modele.md

@@ -103,6 +103,9 @@ erDiagram
     string meal
     int recipeId FK
     int portions
+    int portionsRequested
+    int sourcePlanningItemId FK "nullable, auto-relation"
+    int discardedPortions
   }
   SOURCE {
     int id PK
@@ -264,7 +267,10 @@ pas en avance.
 | `weekDay` | Jour de la semaine |
 | `meal` | Repas concerné |
 | `recipeId` | FK → `recipe` (pas de cascade — voir `RECIPE_IN_USE` dans [error-handling.md](./error-handling.md)) |
-| `portions` | Nombre de portions **pour ce créneau précis** — indépendant de `Recipe.portions` (le rendement "tel qu'écrit" de la recette) : un créneau peut mettre l'échelle à la hausse/baisse. Le picker web pré-remplit depuis `Recipe.portions` mais stocke une valeur propre |
+| `portions` | Portions réellement **préparées** pour ce créneau — toujours un multiple entier de `Recipe.portions` (on cuisine des lots entiers). Dérivé de `portionsRequested` + le rendement de la recette via `computeBatchedPortions` (`@batch-cooking/shared`) dans `addPlanningItem`, jamais saisi tel quel |
+| `portionsRequested` | Portions que ce créneau doit réellement nourrir — le seul nombre saisi à l'ajout. `≤ portions` pour un item frais ; l'écart est le **pool de restes** de cet item |
+| `sourcePlanningItemId` | Auto-FK, non nul uniquement sur un item « restes » : l'item d'origine dont il consomme le pool. `onDelete: Cascade` |
+| `discardedPortions` | Portions du pool de cet item explicitement jetées (bouton « jeter » du panier). `0` par défaut, toujours `0` sur un item « restes » |
 
 ---
 

specs/frontend-architecture.md

@@ -410,8 +410,12 @@ ligne.
    dialogue épinglé ("Confirmer", actif dès qu'une prévisualisation existe)
    est ce qui agit réellement.
 2. **Confirmer les portions** (une vraie recette est prévisualisée) — petit
-   formulaire "combien de portions ?" (pré-rempli depuis
+   formulaire "portions demandées" (pré-rempli depuis
-   `RecipeSummaryView.portions`), puis `POST /planning/items`.
+   `RecipeSummaryView.portions`), avec un indice dérivé en direct via
+   `computeBatchedPortions` (« → N préparées, M en restes ») affiché quand
+   l'arrondi au lot crée un reste (issue #34) ; le corps envoyé à
+   `POST /planning/items` est `portionsRequested` (le serveur calcule
+   `portions`).
 3. **Revue intégrée** (un item de source *pas encore importé* est prévisualisé
    et nécessite une intervention humaine) — rend `RecipeImportForm`
    directement à l'intérieur du même `Dialog` (`planningSlot` transmis pour