feat: regenerate recipe with modifications from the editor

Every existing AI entry point (generate, generate-from-idea, adapt,
variations) either creates a new recipe or a saved variation — none
let you revise the draft you're currently editing in place. Adds a
stateless /api/v1/ai/regenerate endpoint that takes the editor's
current in-progress fields (not a recipeId, so unsaved edits are
included) plus a free-text instruction, and returns a full revised
draft the editor merges into its own state. No DB write happens;
the user still saves normally.

v0.42.0

apps/web/components/recipe/recipe-form.tsx

@@ -24,6 +24,8 @@ import {
 } from "@/components/ui/alert-dialog";
 import { DietaryTagPicker } from "./dietary-tag-picker";
 import { PhotoUploader, type PhotoEntry } from "./photo-uploader";
+import { RegenerateRecipeButton } from "./regenerate-recipe-button";
+import type { RegeneratedRecipe } from "@/lib/ai/features/regenerate-recipe";
 
 type DietaryTags = {
   vegan?: boolean;
@@ -217,6 +219,31 @@ export function RecipeForm({ recipeId, defaultValues }: RecipeFormProps) {
     setIngredients((prev) => prev.filter((_, idx) => idx !== i));
   }
 
+  // Merges an AI-regenerated draft into the in-progress form state — it
+  // never touches the DB directly, so the user still has to hit Save.
+  function applyRegenerated(recipe: RegeneratedRecipe) {
+    setTitle(recipe.title);
+    if (recipe.description !== undefined) setDescription(recipe.description);
+    setBaseServings(String(recipe.baseServings));
+    if (recipe.difficulty) setDifficulty(recipe.difficulty);
+    setPrepMins(recipe.prepMins !== undefined ? String(recipe.prepMins) : "");
+    setCookMins(recipe.cookMins !== undefined ? String(recipe.cookMins) : "");
+    if (recipe.dietaryTags) setDietaryTags(recipe.dietaryTags);
+    setIngredients(recipe.ingredients.map((ing) => ({
+      id: crypto.randomUUID(),
+      rawName: ing.rawName,
+      quantity: ing.quantity !== undefined ? String(ing.quantity) : "",
+      unit: ing.unit ?? "",
+      note: ing.note ?? "",
+    })));
+    setSteps(recipe.steps.map((step) => ({
+      id: crypto.randomUUID(),
+      instruction: step.instruction,
+      timerSeconds: step.timerSeconds !== undefined ? String(step.timerSeconds) : "",
+      appliesTo: [],
+    })));
+  }
+
   function addTag(raw: string) {
     const tag = raw.trim().toLowerCase().slice(0, 50);
     if (!tag || tags.includes(tag) || tags.length >= 20) return;
@@ -392,6 +419,21 @@ export function RecipeForm({ recipeId, defaultValues }: RecipeFormProps) {
     <form onSubmit={handleSubmit} className="space-y-8 max-w-3xl pb-20">
       {/* Basic info */}
       <div className="space-y-4">
+        {isEdit && (
+          <div className="flex justify-end">
+            <RegenerateRecipeButton
+              current={{
+                title,
+                description,
+                baseServings: Number(baseServings) || 1,
+                difficulty,
+                ingredients: ingredients.map((ing) => ({ rawName: ing.rawName, quantity: ing.quantity, unit: ing.unit })),
+                steps: steps.map((step) => ({ instruction: step.instruction })),
+              }}
+              onRegenerated={applyRegenerated}
+            />
+          </div>
+        )}
         <div className="space-y-2">
           <Label htmlFor="title">{t("titleLabel")}</Label>
           <Input