diff --git a/apps/web/cypress/e2e/recipe-form.ts b/apps/web/cypress/e2e/recipe-form.ts
index d655f04..6b214cf 100644
--- a/apps/web/cypress/e2e/recipe-form.ts
+++ b/apps/web/cypress/e2e/recipe-form.ts
@@ -108,7 +108,11 @@ Given("recipe 7 exists with an egg omelette", () => {
     diets: [],
     isFavorite: false,
     ingredients: [{ ingredient: egg, quantity: 3, unit: pieceUnit }],
-    steps: [{ id: 1, description: "Battre les œufs.", picture: null, order: 0 }],
+    // `techSteps: []` matches the real `StepView` shape (packages/shared) —
+    // every other recipe-step mock in the suite sends it, and its absence
+    // here let `/recettes/7` (rendered after this recipe saves) hit
+    // `StepDescription` with `techSteps === undefined`.
+    steps: [{ id: 1, description: "Battre les œufs.", picture: null, order: 0, techSteps: [] }],
   };
   cy.intercept("GET", "**/recipes/7", { statusCode: 200, body: existingRecipe });
 });
diff --git a/apps/web/cypress/e2e/recipes.cy.ts b/apps/web/cypress/e2e/recipes.cy.ts
index 137dcd9..c6eebf6 100644
--- a/apps/web/cypress/e2e/recipes.cy.ts
+++ b/apps/web/cypress/e2e/recipes.cy.ts
@@ -166,6 +166,29 @@ const brownStepRecipe = {
   ],
 };
 
+/**
+ * A recipe whose step object is missing `techSteps` entirely (not `[]`) —
+ * a partial/older payload shape. `StepDescription` must render its
+ * description as plain text rather than crashing on `liveTechSteps.flatMap`.
+ * Regression: an intermittent `recipe-form.feature` failure where saving an
+ * edited recipe navigates to `/recettes/:id`, whose detail loaded before
+ * `techSteps` was populated.
+ */
+const techStepsMissingDetail = {
+  id: 7,
+  name: "Omelette",
+  description: null,
+  picture: null,
+  portions: 2,
+  authorId: 1,
+  visibility: "PERSONAL",
+  allergens: [],
+  diets: [],
+  isFavorite: false,
+  ingredients: [],
+  steps: [{ id: 1, description: "Battre les œufs.", picture: null, order: 1 }],
+};
+
 function interceptAuth() {
   cy.intercept("GET", "**/auth/me", { statusCode: 200, body: authenticatedProfile });
   cy.intercept("GET", "**/profile/disliked-ingredients", { statusCode: 200, body: [] });
@@ -284,6 +307,27 @@ describe("Recipe catalog", () => {
     });
   });
 
+  // Regression: a step payload missing `techSteps` entirely (see
+  // `techStepsMissingDetail`) made `StepDescription` throw
+  // `Cannot read properties of undefined (reading 'flatMap')`, surfacing as
+  // an uncaught application error. An uncaught exception fails the spec on
+  // its own, so simply asserting the description renders is enough — no
+  // extra `cy.on("uncaught:exception")` needed.
+  it("renders a step whose techSteps field is absent from the payload, as plain text", () => {
+    cy.viewport(1600, 900);
+    cy.intercept("GET", /\/recipes\?/, { statusCode: 200, body: [] });
+    cy.intercept("GET", "**/recipes/7", { statusCode: 200, body: techStepsMissingDetail }).as(
+      "getRecipe",
+    );
+
+    cy.visit("/recettes/7");
+    cy.wait("@getRecipe");
+
+    cy.get(".recipe-detail-panel__steps").within(() => {
+      cy.contains("Battre les œufs.").should("be.visible");
+    });
+  });
+
   // Regression: `.recipe-detail-panel__steps`'s CSS step counter
   // (recipes.scss) used a bare descendant `li` selector, matching *any*
   // `<li>` nested inside a step — including ones several levels down
diff --git a/apps/web/src/features/recipes/steps/StepDescription.tsx b/apps/web/src/features/recipes/steps/StepDescription.tsx
index 5fb0e4a..eb79903 100644
--- a/apps/web/src/features/recipes/steps/StepDescription.tsx
+++ b/apps/web/src/features/recipes/steps/StepDescription.tsx
@@ -71,14 +71,15 @@ function findTechStepForTemperature(
  * no click handlers) — this mode is purely additive, not a rewrite of the
  * read-only rendering.
  *
- * Maintains its own local copy of `techSteps` (seeded from the prop, then
- * replaced with whatever `POST .../corrections` returns on a successful
- * submit — see `SubmitTechStepCorrectionResult`'s doc comment,
- * `packages/shared`) so a correction's effect (a new/relabeled/removed
- * highlight) appears immediately, without needing the parent to re-fetch
- * the whole recipe. Resynced whenever the `techSteps` prop itself changes
- * (e.g. the parent reloaded the recipe for an unrelated reason) so this
- * never keeps showing stale local state past that.
+ * Maintains its own local copy of `techSteps` (seeded from the prop — or
+ * `[]` if it's momentarily absent, see the prop's own note — then replaced
+ * with whatever `POST .../corrections` returns on a successful submit — see
+ * `SubmitTechStepCorrectionResult`'s doc comment, `packages/shared`) so a
+ * correction's effect (a new/relabeled/removed highlight) appears
+ * immediately, without needing the parent to re-fetch the whole recipe.
+ * Resynced whenever the `techSteps` prop itself changes (e.g. the parent
+ * reloaded the recipe for an unrelated reason) so this never keeps showing
+ * stale local state past that.
  */
 export function StepDescription({
   description,
@@ -88,15 +89,32 @@ export function StepDescription({
   stepId,
 }: {
   description: string;
-  techSteps: StepTechStepView[];
+  /**
+   * The step's detected technique sequence. `StepView.techSteps`
+   * (`packages/shared`) always sends an array — `[]` when nothing matched —
+   * but this is optional so a partial/not-yet-resolved payload degrades to
+   * "render the description as plain text" instead of crashing on
+   * `.flatMap`, the same "tolerate missing data, don't crash" posture this
+   * component already takes for a match with no `contextStart`/`contextEnd`
+   * or a temperature with no owning occurrence. Seen `undefined` in
+   * practice on the post-save navigation of the "edit an existing recipe"
+   * flow, before the reloaded recipe's detail had resolved
+   * (`recipe-form.feature`).
+   */
+  techSteps?: StepTechStepView[];
   /** Requires `recipeId`/`stepId` when `true` — omit (or leave `false`) for a read-only view with nothing real to correct against yet (e.g. `RecipeDetailPanel`'s `"loaded-draft"` unsaved-preview branch). */
   editable?: boolean;
   recipeId?: number;
   stepId?: number;
 }) {
   const { t } = useTranslation();
-  const [liveTechSteps, setLiveTechSteps] = useState(techSteps);
-  useEffect(() => setLiveTechSteps(techSteps), [techSteps]);
+  // `?? []` here, not just at each read site, so every consumer below
+  // (`.flatMap` for `temperatures`, `splitDescriptionSegments`,
+  // `findTechStepForTemperature`, the `activeStepTechStep` lookup) always
+  // has a real array — see the `techSteps` prop's own note for when it
+  // arrives absent.
+  const [liveTechSteps, setLiveTechSteps] = useState(techSteps ?? []);
+  useEffect(() => setLiveTechSteps(techSteps ?? []), [techSteps]);
 
   // Temperatures are attached per technique-clause server-side; for the
   // read-only highlight we only care *where* in the description they are,