3c: partial consumption + undo for cooking sessions

- Append-only undo via correction transactions tied to cookingSessionId.
- POST /v1/cooking-sessions/:id/undo with 24h UTC window (409 + i18n after expiry).
- Complete undo scope: meals removed, meal boxes discarded, recipe_cooks
deleted, cookCount decremented; activation milestones left intact.
- Deterministic assumption-profile rollback via lastSessionAnswers.sessionId;
profile deleted when observationCount reaches 0.
- New status 'undone' as TEXT validated against COOKING_SESSION_STATUSES.
- Analytics event cooking_session_undone + domain events MEAL_BOX_DISCARDED,
MEAL_REMOVED, COOKING_SESSION_UNDONE.
- Partial consumption uses actualPortionsEaten/plannedPortions factor.
- i18n coverage for cooked.undoWindowExpired across all 12 locales + server.
- Invariant tests: computeBalance(transactions) === item.quantity after
complete, undo, and undo + new complete; transaction count increases on undo.
- Migration 0014_expand_event_types.sql adds new enum values.
- Updated FAS3-COOKING-SESSIONS-AUDIT.md with chosen semantics.

packages/inventory-engine/src/cooking-profiles.ts

@@ -55,6 +55,51 @@ export function updateCookingAssumptionProfile(
   return { averageEatenPortions, averageLeftoverPortions, observationCount, lastSessionAnswers };
 }
 
+/**
+ * Återställ en antagandeprofil genom att ta bort ett specifikt sessions-id
+ * från historiken och räkna om medelvärdena deterministiskt från resterande
+ * observationer. Ren funktion – alla beroenden är explicita argument.
+ */
+export function rollbackCookingAssumptionProfile(
+  sessionId: string,
+  existing: ExistingProfile,
+): {
+  averageEatenPortions: number | null;
+  averageLeftoverPortions: number | null;
+  observationCount: number;
+  lastSessionAnswers: Array<{ sessionId: string; eaten: number; leftovers: number; date: string }>;
+} {
+  const history = (existing.lastSessionAnswers ?? []).filter((a) => a.sessionId !== sessionId);
+
+  if (history.length === 0) {
+    return {
+      averageEatenPortions: null,
+      averageLeftoverPortions: null,
+      observationCount: 0,
+      lastSessionAnswers: [],
+    };
+  }
+
+  // Räkna om EMA från scratch i kronologisk ordning (äldst först).
+  const chronological = [...history].reverse();
+  let avgEaten = chronological[0]!.eaten;
+  let avgLeftovers = chronological[0]!.leftovers;
+
+  for (let i = 1; i < chronological.length; i++) {
+    const alpha = 1 / (i + 1);
+    const a = chronological[i]!;
+    avgEaten = round2(avgEaten + alpha * (a.eaten - avgEaten));
+    avgLeftovers = round2(avgLeftovers + alpha * (a.leftovers - avgLeftovers));
+  }
+
+  return {
+    averageEatenPortions: avgEaten,
+    averageLeftoverPortions: avgLeftovers,
+    observationCount: history.length,
+    lastSessionAnswers: history,
+  };
+}
+
 function clamp(n: number, min: number, max: number): number {
   return Math.max(min, Math.min(max, n));
 }

packages/inventory-engine/test/cooking-profiles.test.ts

@@ -1,5 +1,8 @@
 import { describe, expect, it } from "vitest";
-import { updateCookingAssumptionProfile } from "../src/cooking-profiles.js";
+import {
+  updateCookingAssumptionProfile,
+  rollbackCookingAssumptionProfile,
+} from "../src/cooking-profiles.js";
 
 describe("updateCookingAssumptionProfile", () => {
   it("initializes profile from first observation", () => {
@@ -61,3 +64,104 @@ describe("updateCookingAssumptionProfile", () => {
     expect(existing.lastSessionAnswers![0]!.sessionId).toBe("s11");
   });
 });
+
+describe("rollbackCookingAssumptionProfile", () => {
+  it("returns null averages and zero count when history becomes empty", () => {
+    const existing = updateCookingAssumptionProfile(
+      {
+        householdId: "h1",
+        canonicalIngredientId: "i1",
+        plannedPortions: 4,
+        actualPortionsEaten: 3,
+        leftoverEstimatePortions: 1,
+        sessionId: "s1",
+        date: "2026-08-07",
+      },
+      { averageEatenPortions: null, averageLeftoverPortions: null, observationCount: 0 },
+    );
+    const rolled = rollbackCookingAssumptionProfile("s1", existing);
+    expect(rolled.averageEatenPortions).toBeNull();
+    expect(rolled.averageLeftoverPortions).toBeNull();
+    expect(rolled.observationCount).toBe(0);
+    expect(rolled.lastSessionAnswers).toHaveLength(0);
+  });
+
+  it("recalculates averages deterministically from remaining history", () => {
+    let existing: {
+      averageEatenPortions: number | null;
+      averageLeftoverPortions: number | null;
+      observationCount: number;
+      lastSessionAnswers?: Array<{ sessionId: string; eaten: number; leftovers: number; date: string }> | null;
+    } = { averageEatenPortions: null, averageLeftoverPortions: null, observationCount: 0 };
+
+    // Three chronological observations.
+    const observations = [
+      { sessionId: "s1", eaten: 4, leftovers: 0 },
+      { sessionId: "s2", eaten: 2, leftovers: 1 },
+      { sessionId: "s3", eaten: 3, leftovers: 1 },
+    ];
+    for (const obs of observations) {
+      existing = updateCookingAssumptionProfile(
+        {
+          householdId: "h1",
+          canonicalIngredientId: "i1",
+          plannedPortions: 4,
+          actualPortionsEaten: obs.eaten,
+          leftoverEstimatePortions: obs.leftovers,
+          sessionId: obs.sessionId,
+          date: "2026-08-07",
+        },
+        existing,
+      );
+    }
+
+    // Roll back the middle observation and recompute from scratch.
+    const rolled = rollbackCookingAssumptionProfile("s2", existing);
+    expect(rolled.lastSessionAnswers).toHaveLength(2);
+    expect(rolled.lastSessionAnswers!.map((a) => a.sessionId)).toContain("s1");
+    expect(rolled.lastSessionAnswers!.map((a) => a.sessionId)).toContain("s3");
+
+    // Recompute EMA manually from s1 then s3.
+    // s1: avgEaten=4, avgLeftovers=0
+    // s3: alpha=1/2 => eaten=4+0.5*(3-4)=3.5, leftovers=0+0.5*(1-0)=0.5
+    expect(rolled.averageEatenPortions).toBe(3.5);
+    expect(rolled.averageLeftoverPortions).toBe(0.5);
+    expect(rolled.observationCount).toBe(2);
+  });
+
+  it("is idempotent: rolling back the same session twice leaves history unchanged", () => {
+    let existing: {
+      averageEatenPortions: number | null;
+      averageLeftoverPortions: number | null;
+      observationCount: number;
+      lastSessionAnswers?: Array<{ sessionId: string; eaten: number; leftovers: number; date: string }> | null;
+    } = { averageEatenPortions: null, averageLeftoverPortions: null, observationCount: 0 };
+    existing = updateCookingAssumptionProfile(
+      {
+        householdId: "h1",
+        canonicalIngredientId: "i1",
+        plannedPortions: 4,
+        actualPortionsEaten: 3,
+        leftoverEstimatePortions: 1,
+        sessionId: "s1",
+        date: "2026-08-07",
+      },
+      existing,
+    );
+    existing = updateCookingAssumptionProfile(
+      {
+        householdId: "h1",
+        canonicalIngredientId: "i1",
+        plannedPortions: 4,
+        actualPortionsEaten: 2,
+        leftoverEstimatePortions: 0,
+        sessionId: "s2",
+        date: "2026-08-07",
+      },
+      existing,
+    );
+    const first = rollbackCookingAssumptionProfile("s1", existing);
+    const second = rollbackCookingAssumptionProfile("s1", first);
+    expect(second).toEqual(first);
+  });
+});