diff --git a/apps/web/cypress/e2e/layout.cy.ts b/apps/web/cypress/e2e/layout.cy.ts
index 4369ea5..65f6589 100644
--- a/apps/web/cypress/e2e/layout.cy.ts
+++ b/apps/web/cypress/e2e/layout.cy.ts
@@ -172,44 +172,78 @@ describe("Page width — full-bleed pages vs. centered reading columns (#21 regr
   }
 });
 
-describe("Responsive breakpoint — sidebar becomes a horizontal top bar under 640px", () => {
+describe("Responsive breakpoint — the sidebar becomes a bottom tab bar under 640px", () => {
+  // Regression coverage for the mobile/tablet UI chantier's foundation
+  // ticket: below this point the desktop `<aside>` sidebar isn't reflowed
+  // by CSS anymore, it's replaced outright by a fixed bottom nav (a
+  // genuinely different component tree — see AppLayout.tsx's own doc
+  // comment on why). This block used to test the old CSS-squash treatment
+  // (sidebar → horizontal top bar); that treatment no longer exists.
   beforeEach(() => {
     interceptAuth();
     cy.intercept("GET", /\/planning\?/, { statusCode: 200, body: null });
   });
 
-  it("switches to a full-width horizontal bar, hides the collapse toggle and version tag, and keeps every nav link legible", () => {
+  it("renders the bottom nav instead of the sidebar, with every route tab legible and a working Plus tab", () => {
     cy.viewport(375, 812);
     cy.visit("/");
 
-    cy.get(".app-sidebar").should(($sidebar) => {
-      const rect = $sidebar[0].getBoundingClientRect();
+    // The desktop sidebar isn't just hidden — it's not in the DOM at all.
+    cy.get(".app-sidebar").should("not.exist");
+
+    cy.get(".app-bottom-nav").should(($nav) => {
+      const rect = $nav[0].getBoundingClientRect();
       expect(rect.width).to.be.closeTo(375, 1);
-      // A short horizontal bar, not the tall vertical rail — well under the
-      // desktop rail's own content-driven height.
+      // A short bar flush against the bottom edge, not a tall rail.
       expect(rect.height).to.be.lessThan(120);
+      expect(rect.bottom).to.be.closeTo(812, 1);
+      expect(getComputedStyle($nav[0]).position).to.equal("fixed");
     });
 
-    // Nothing to collapse into on a bar with no rail to shrink.
-    cy.get(".app-sidebar__collapse-toggle").should("not.be.visible");
-    cy.get(".app-sidebar__version").should("not.be.visible");
+    // Every route tab keeps its icon *and* label legible — this bar never
+    // falls back to icon-only or horizontal scroll, unlike the old
+    // squashed sidebar treatment it replaces (only 4 short tabs, always
+    // fits).
+    cy.contains(".app-bottom-nav a", "Planning").find("span.label").should("be.visible");
+    cy.contains(".app-bottom-nav a", "Recettes").should("have.attr", "href", "/recettes");
+    cy.contains(".app-bottom-nav a", "Liste de courses").should(
+      "have.attr",
+      "href",
+      "/liste-de-courses",
+    );
 
-    // The main nav must stay fully legible and tappable — icon *and* label
-    // — falling back to horizontal scroll instead of ever being crushed
-    // down to unlabeled slivers (see AppLayout.scss's own comment on this
-    // exact failure mode).
-    cy.get(".app-sidebar__nav").should(($nav) => {
-      expect(getComputedStyle($nav[0]).overflowX).to.equal("auto");
-    });
-    cy.contains(".app-sidebar__nav a", "Planning").find("span.label").should("be.visible");
-    cy.contains(".app-sidebar__nav a", "Planning").should(($link) => {
-      expect($link[0].getBoundingClientRect().width).to.be.greaterThan(40);
-    });
+    // The "Plus" tab opens a bottom sheet with Paramètres + Compte, closed
+    // by default.
+    cy.get(".bottom-sheet").should("not.exist");
+    cy.contains(".app-bottom-nav button", "Plus").click();
 
-    // Contrast: the settings/account toggles' labels *do* collapse to
-    // icon-only here — there's no room for both a full nav row and full
-    // text labels on every piece of chrome at once.
-    cy.contains("button", "Paramètres").find("span.label").should("not.be.visible");
+    cy.get(".bottom-sheet").should("be.visible");
+    cy.contains(".bottom-sheet", "Bonjour Alice").should("be.visible");
+    cy.contains(".bottom-sheet a", "Compte").should("have.attr", "href", "/parametres/compte");
+    cy.contains(".bottom-sheet a", "Préférences alimentaires").should(
+      "have.attr",
+      "href",
+      "/parametres/preferences",
+    );
+    cy.contains(".bottom-sheet button", "Se déconnecter").should("be.visible");
+
+    // The close button calls the native `<dialog>`'s own `.close()`, whose
+    // `close` event `useNativeDialogBehavior` forwards back to
+    // `MobileBottomNav`'s own state — same wiring Escape/tap-outside use,
+    // exercised here since it doesn't depend on this Cypress/Electron
+    // environment faithfully replicating the browser's own native
+    // Escape-closes-a-modal-dialog behavior (a browser built-in this app
+    // doesn't implement itself — see Dialog.tsx's own doc comment).
+    cy.get(".bottom-sheet__close").click();
+    cy.get(".bottom-sheet").should("not.exist");
+  });
+
+  it("keeps the desktop sidebar (not the bottom nav) above the phone breakpoint", () => {
+    cy.viewport(1000, 700);
+    cy.visit("/");
+
+    cy.get(".app-sidebar").should("exist");
+    cy.get(".app-bottom-nav").should("not.exist");
   });
 });
 
diff --git a/apps/web/src/components/ui/BottomSheet.tsx b/apps/web/src/components/ui/BottomSheet.tsx
new file mode 100644
index 0000000..c33b3e0
--- /dev/null
+++ b/apps/web/src/components/ui/BottomSheet.tsx
@@ -0,0 +1,65 @@
+import type { ReactNode } from "react";
+import "./bottom-sheet.scss";
+import { useNativeDialogBehavior } from "./useNativeDialogBehavior";
+
+/**
+ * A native `<dialog>` anchored to the bottom edge instead of centered —
+ * the mobile-native replacement for a small anchored floating popover
+ * (a menu, a short list of actions) that a phone-width screen has no good
+ * place to float. Same open/close mechanics as `Dialog.tsx` (via the
+ * shared `useNativeDialogBehavior`: `showModal()` on mount, Escape/`close`
+ * event, tap-outside-to-dismiss) — only the panel's own position/shape
+ * differs, so both get the browser's focus trap and top-layer stacking for
+ * free.
+ *
+ * First consumer: `AppLayout`'s mobile nav, for the "Plus" tab (Paramètres
+ * + Compte, previously two separate floating dropdowns that had no
+ * viewport-edge handling at all — see the mobile/tablet UI chantier's own
+ * audit). Meant to be reused by the planning popovers (leftovers basket,
+ * week calendar) in a later ticket of that same chantier — kept generic
+ * (title + children, no planning-specific assumptions) for that reason.
+ *
+ * Not used on desktop: a sheet sliding up from the bottom of a full
+ * viewport only reads as "anchored to what you tapped" on a narrow screen
+ * where the tapped control is usually near the bottom already (a bottom
+ * tab bar, a floating action button). Desktop keeps the existing anchored
+ * dropdown/popover pattern for the same triggers — callers decide which to
+ * render (typically via `useIsMobileViewport()`), this component doesn't
+ * check the viewport itself.
+ */
+export function BottomSheet({
+  onClose,
+  title,
+  children,
+}: {
+  onClose: () => void;
+  title?: string;
+  children: ReactNode;
+}) {
+  const dialogRef = useNativeDialogBehavior(onClose);
+
+  return (
+    <dialog ref={dialogRef} className="bottom-sheet" aria-label={title}>
+      {/* Purely decorative drag-affordance — this sheet closes via
+          tap-outside/Escape/the close button, never an actual drag
+          gesture, but the grabber bar is still the expected visual
+          convention for "this slid up from the bottom" on both Android and
+          iOS, so it's worth keeping even without the gesture behind it. */}
+      <div className="bottom-sheet__grabber" aria-hidden="true" />
+      {title && (
+        <div className="bottom-sheet__header">
+          <h2>{title}</h2>
+          <button
+            type="button"
+            className="bottom-sheet__close"
+            onClick={() => dialogRef.current?.close()}
+            aria-label="Fermer"
+          >
+            ✕
+          </button>
+        </div>
+      )}
+      <div className="bottom-sheet__body">{children}</div>
+    </dialog>
+  );
+}
diff --git a/apps/web/src/components/ui/Dialog.tsx b/apps/web/src/components/ui/Dialog.tsx
index c451f41..a90b5e7 100644
--- a/apps/web/src/components/ui/Dialog.tsx
+++ b/apps/web/src/components/ui/Dialog.tsx
@@ -1,5 +1,6 @@
-import { type ReactNode, useEffect, useRef } from "react";
+import type { ReactNode } from "react";
 import "./dialog.scss";
+import { useNativeDialogBehavior } from "./useNativeDialogBehavior";
 
 /**
  * App-wide modal primitive — a native `<dialog>` (`showModal()`), not a
@@ -11,6 +12,14 @@ import "./dialog.scss";
  * overlay; a full recipe catalog + filters (`RecipePickerDialog`) doesn't
  * fit inline, hence this.
  *
+ * On a phone (`_breakpoints.scss`'s `$phone`) the panel goes edge-to-edge
+ * full screen instead of staying a centered, rounded panel — see
+ * `dialog.scss`'s own comment on why a shrunk desktop dialog isn't enough
+ * on a small screen. `BottomSheet` (this same folder) is the sibling
+ * primitive for a *permanently* bottom-anchored overlay (a menu/popover),
+ * not a full modal — the two share their open/close mechanics via
+ * `useNativeDialogBehavior` but stay visually and semantically distinct.
+ *
  * Mounted only while open (see `PlanningPage`'s conditional rendering of
  * `RecipePickerDialog`, same convention as its own `CalendarPopover`) —
  * `showModal()` fires once on mount rather than toggling on an `isOpen`
@@ -31,56 +40,7 @@ export function Dialog({
   /** Optional action bar pinned below the scrollable body (`.dialog-panel__footer`) — outside `.dialog-panel__body`'s own scroll, same idea as `title`'s header. Omit for a plain dialog with no persistent footer actions. */
   footer?: ReactNode;
 }) {
-  const dialogRef = useRef<HTMLDialogElement>(null);
-
-  useEffect(() => {
-    dialogRef.current?.showModal();
-  }, []);
-
-  useEffect(() => {
-    const dialog = dialogRef.current;
-    if (!dialog) return;
-    // `close` covers every way a native dialog can close — Escape (which
-    // fires `cancel` first, then `close`) as much as a future
-    // `<form method="dialog">` — so this is the one listener needed to
-    // keep the caller's own "is this open" state (e.g. `PlanningPage`'s
-    // `openSlot`) in sync with it.
-    dialog.addEventListener("close", onClose);
-    return () => dialog.removeEventListener("close", onClose);
-  }, [onClose]);
-
-  useEffect(() => {
-    const dialog = dialogRef.current;
-    if (!dialog) return;
-    // Attached imperatively (not a JSX `onClick`) since the click-to-close
-    // it implements is already reachable from the keyboard via Escape
-    // (native `cancel`/`close`, wired above) — a JSX `onClick` here would
-    // trip the "needs a matching keyboard handler" a11y lint for a
-    // non-interactive element even though one already exists, just not in
-    // a form that lint rule can see.
-    function handleClick(e: MouseEvent) {
-      // Re-read from the ref (not the outer `dialog` const) — TS can't
-      // carry that early-return narrowing into a nested function, since it
-      // can't prove the function won't run at some later point where it no
-      // longer holds (even though here, as an event listener on this same
-      // element, it trivially still does).
-      const current = dialogRef.current;
-      if (!current) return;
-      // A click lands on the `<dialog>` element itself both for the
-      // backdrop *and* for its own unfilled padding/margin — comparing
-      // against its content box (not just `e.target`) is what actually
-      // distinguishes "outside the panel" from "on it".
-      const rect = current.getBoundingClientRect();
-      const inside =
-        e.clientX >= rect.left &&
-        e.clientX <= rect.right &&
-        e.clientY >= rect.top &&
-        e.clientY <= rect.bottom;
-      if (!inside) current.close();
-    }
-    dialog.addEventListener("click", handleClick);
-    return () => dialog.removeEventListener("click", handleClick);
-  }, []);
+  const dialogRef = useNativeDialogBehavior(onClose);
 
   return (
     <dialog
diff --git a/apps/web/src/components/ui/bottom-sheet.scss b/apps/web/src/components/ui/bottom-sheet.scss
new file mode 100644
index 0000000..54ec948
--- /dev/null
+++ b/apps/web/src/components/ui/bottom-sheet.scss
@@ -0,0 +1,76 @@
+// Bottom-anchored panel — see BottomSheet.tsx. A native <dialog> opened via
+// showModal(), same UA-default reset as dialog.scss, but positioned flush
+// against the bottom edge instead of centered.
+
+.bottom-sheet {
+  display: flex;
+  flex-direction: column;
+  width: 100%;
+  max-width: 32rem; // caps how wide this gets on a tablet-width viewport
+  max-height: min(80vh, 40rem);
+  // A native <dialog>'s UA default is `position: fixed; inset: 0; margin:
+  // auto` (centered) — overriding just the vertical half of that margin
+  // pins it to the bottom edge while `margin-inline: auto` keeps it
+  // horizontally centered (relevant once `max-width` is narrower than the
+  // viewport, e.g. on a tablet).
+  margin: 0 auto auto;
+  padding: 0;
+  border: none;
+  background: var(--color-surface);
+  color: var(--color-text);
+  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
+  box-shadow: var(--shadow-md);
+  overflow: hidden;
+
+  &::backdrop {
+    background: rgba(0, 0, 0, 0.45);
+  }
+}
+
+.bottom-sheet__grabber {
+  flex-shrink: 0;
+  width: 2.5rem;
+  height: 0.25rem;
+  margin: var(--space-sm) auto;
+  border-radius: var(--radius-pill);
+  background: var(--color-border);
+}
+
+.bottom-sheet__header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: var(--space-md);
+  padding: 0 var(--space-lg) var(--space-md);
+
+  h2 {
+    font-size: var(--font-size-lg);
+  }
+}
+
+.bottom-sheet__close {
+  flex: none;
+  width: 2rem;
+  height: 2rem;
+  border: none;
+  border-radius: var(--radius-base);
+  background: transparent;
+  color: var(--color-text-muted);
+  font-size: var(--font-size-md);
+  cursor: pointer;
+
+  &:hover {
+    background: var(--color-surface-alt);
+    color: var(--color-text);
+  }
+}
+
+.bottom-sheet__body {
+  flex: 1;
+  min-height: 0;
+  overflow-y: auto;
+  // A phone's bottom safe area (gesture bar / rounded corners) sits right
+  // below this sheet's own bottom edge — the extra bottom padding keeps the
+  // last item from ever feeling flush against it.
+  padding: 0 var(--space-lg) var(--space-lg);
+}
diff --git a/apps/web/src/components/ui/dialog.scss b/apps/web/src/components/ui/dialog.scss
index 5948032..9e0a754 100644
--- a/apps/web/src/components/ui/dialog.scss
+++ b/apps/web/src/components/ui/dialog.scss
@@ -5,6 +5,8 @@
 // since it's one component's styling, same convention as every feature's
 // own .scss file (recipes.scss, planning-page.scss, …).
 
+@use "../../styles/breakpoints" as bp;
+
 .dialog-panel {
   display: flex;
   flex-direction: column;
@@ -24,14 +26,18 @@
     background: rgba(0, 0, 0, 0.45);
   }
 
-  // On a phone the `48rem` cap is irrelevant (the viewport is narrower),
-  // but the `var(--space-2xl)` top/bottom breathing room is a large slice
-  // of a short screen — tighten it so a form-heavy dialog isn't
-  // needlessly cramped, and keep a small side gutter so the panel never
-  // sits edge to edge.
-  @media (max-width: 640px) {
-    max-width: calc(100vw - var(--space-md));
-    max-height: calc(100vh - var(--space-md));
+  // A shrunk-but-still-centered panel (the old phone treatment here — just
+  // tighter margins) still wastes a meaningful slice of a ~375px screen on
+  // rounded corners + drop shadow + surrounding backdrop, and still needs
+  // its own internal scroll for anything longer than a short form. Full
+  // screen removes all of that: the panel just *is* the screen, so there's
+  // nothing left to reflow around.
+  @include bp.phone {
+    max-width: 100vw;
+    max-height: 100vh;
+    height: 100vh;
+    border-radius: 0;
+    box-shadow: none;
   }
 }
 
diff --git a/apps/web/src/components/ui/useNativeDialogBehavior.ts b/apps/web/src/components/ui/useNativeDialogBehavior.ts
new file mode 100644
index 0000000..a0b1e28
--- /dev/null
+++ b/apps/web/src/components/ui/useNativeDialogBehavior.ts
@@ -0,0 +1,69 @@
+import { useEffect, useRef } from "react";
+
+/**
+ * The mechanics every native `<dialog>`-based overlay in this app needs,
+ * factored out of `Dialog.tsx` once `BottomSheet.tsx` needed the exact same
+ * three behaviors with only its CSS differing: open via `showModal()` on
+ * mount, forward the native `close` event (covers Escape and any future
+ * `<form method="dialog">`) to the caller's own `onClose`, and treat a
+ * click that lands outside the panel's own content box as "close" (a click
+ * on the `<dialog>` element itself, since it fills the viewport, is what a
+ * backdrop click looks like — there's no separate `::backdrop` element to
+ * attach a listener to).
+ *
+ * Returns just the ref — callers still own their own JSX/className, this
+ * only owns the imperative wiring. No explicit return type annotation on
+ * purpose: `useRef<HTMLDialogElement>(null)`'s inferred type is exactly
+ * what JSX's `ref` prop expects, but spelling that same type out by hand
+ * (`RefObject<HTMLDialogElement | null>`) is subtly different and doesn't
+ * satisfy it — let inference carry it through instead of re-typing it.
+ */
+export function useNativeDialogBehavior(onClose: () => void) {
+  const dialogRef = useRef<HTMLDialogElement>(null);
+
+  useEffect(() => {
+    dialogRef.current?.showModal();
+  }, []);
+
+  useEffect(() => {
+    const dialog = dialogRef.current;
+    if (!dialog) return;
+    dialog.addEventListener("close", onClose);
+    return () => dialog.removeEventListener("close", onClose);
+  }, [onClose]);
+
+  useEffect(() => {
+    const dialog = dialogRef.current;
+    if (!dialog) return;
+    // Attached imperatively (not a JSX `onClick`) since the click-to-close
+    // it implements is already reachable from the keyboard via Escape
+    // (native `cancel`/`close`, wired above) — a JSX `onClick` here would
+    // trip the "needs a matching keyboard handler" a11y lint for a
+    // non-interactive element even though one already exists, just not in
+    // a form that lint rule can see.
+    function handleClick(e: MouseEvent) {
+      // Re-read from the ref (not the outer `dialog` const) — TS can't
+      // carry that early-return narrowing into a nested function, since it
+      // can't prove the function won't run at some later point where it no
+      // longer holds (even though here, as an event listener on this same
+      // element, it trivially still does).
+      const current = dialogRef.current;
+      if (!current) return;
+      // A click lands on the `<dialog>` element itself both for the
+      // backdrop *and* for its own unfilled padding/margin — comparing
+      // against its content box (not just `e.target`) is what actually
+      // distinguishes "outside the panel" from "on it".
+      const rect = current.getBoundingClientRect();
+      const inside =
+        e.clientX >= rect.left &&
+        e.clientX <= rect.right &&
+        e.clientY >= rect.top &&
+        e.clientY <= rect.bottom;
+      if (!inside) current.close();
+    }
+    dialog.addEventListener("click", handleClick);
+    return () => dialog.removeEventListener("click", handleClick);
+  }, []);
+
+  return dialogRef;
+}
diff --git a/apps/web/src/features/planning/recipe-picker-dialog.scss b/apps/web/src/features/planning/recipe-picker-dialog.scss
index 45c78d8..edddd46 100644
--- a/apps/web/src/features/planning/recipe-picker-dialog.scss
+++ b/apps/web/src/features/planning/recipe-picker-dialog.scss
@@ -4,6 +4,8 @@
 // `.field-error` come from recipes.scss (already loaded — RecipeTable /
 // RecipeTabs import it themselves).
 
+@use "../../styles/breakpoints" as bp;
+
 .recipe-picker-dialog {
   width: 95vw;
   max-width: 85rem;
@@ -61,7 +63,7 @@
   // `@media` block and would keep two ~90px columns side by side on a
   // phone. Re-collapse it here for the dialog's own narrow case — the list
   // then stacks above the detail pane, same as the full `/recettes` page.
-  @media (max-width: 640px) {
+  @include bp.phone {
     .recipes-page__catalog {
       grid-template-columns: 1fr;
     }
diff --git a/apps/web/src/features/recipes/recipes.scss b/apps/web/src/features/recipes/recipes.scss
index 8f6b260..a87c0a8 100644
--- a/apps/web/src/features/recipes/recipes.scss
+++ b/apps/web/src/features/recipes/recipes.scss
@@ -11,6 +11,8 @@
 // resolves per-theme globally (see styles/_theme.scss).
 // =============================================================================
 
+@use "../../styles/breakpoints" as bp;
+
 // --- Allergen / diet / disliked-ingredient badges ---------------------------
 // Three visually distinct pill languages, each with its own meaning — never
 // mixed, so a glance tells them apart without reading the label:
@@ -166,7 +168,7 @@
     gap: var(--space-lg);
   }
 
-  @media (max-width: 1024px) {
+  @include bp.tablet-down {
     &__catalog {
       grid-template-columns: 1fr;
       // The single-row `1fr` track above only makes sense for the desktop
diff --git a/apps/web/src/layouts/AppLayout.scss b/apps/web/src/layouts/AppLayout.scss
index efa950a..b91fca7 100644
--- a/apps/web/src/layouts/AppLayout.scss
+++ b/apps/web/src/layouts/AppLayout.scss
@@ -6,6 +6,10 @@
 
 // No `@use` of the theme partial needed here — see HomePage.scss's identical
 // note: every token below is a CSS custom property, available at runtime.
+// Breakpoints are the one exception (a `@media` condition can't read a CSS
+// custom property, see `_breakpoints.scss`'s own doc comment) — that partial
+// still needs a real Sass `@use`.
+@use "../styles/breakpoints" as bp;
 
 // `height` (not `min-height`): the layout must stay pinned to exactly the
 // viewport, never grow taller than it — otherwise a tall page scrolls the
@@ -265,16 +269,17 @@
   // just hides labels/chevrons and re-centers icons via CSS, no child
   // component needs to know the sidebar is collapsed.
   //
-  // Scoped to `min-width: 641px` (the exact complement of the mobile
-  // `@media (max-width: 640px)` block below): `isCollapsed` persists in
-  // `localStorage` (`batchcooking:sidebarCollapsed`) independently of
-  // viewport width, so a user who collapsed the desktop rail and then
-  // shrinks the window (or opens the same session on a phone) still carries
-  // that flag. Without this guard, `.app-sidebar.collapsed`'s `width:
-  // 4.25rem`/`flex-direction: column` (specificity 0,2,0) beat the mobile
-  // block's `.app-sidebar` rules (specificity 0,1,0) and crushed the
-  // full-width horizontal bar into a tiny broken rail — see issue #27.
-  @media (min-width: 641px) {
+  // Scoped to phone-up (`_breakpoints.scss`'s exact complement of the phone
+  // breakpoint): `isCollapsed` persists in `localStorage`
+  // (`batchcooking:sidebarCollapsed`) independently of viewport width, so a
+  // user who collapsed the desktop rail and then shrinks the window still
+  // carries that flag. This guard used to matter for a second reason too —
+  // on a phone, `.app-sidebar` isn't even rendered anymore at all (see
+  // AppLayout.tsx: the mobile bottom nav is a fully separate component tree,
+  // not this same `<aside>` reflowed by CSS, unlike issue #27's original
+  // fix here) — but the explicit width guard is kept regardless, since nothing
+  // stops a future phone-width variant of `.app-sidebar` from existing again.
+  @include bp.phone-up {
     &.collapsed {
       width: 4.25rem;
       padding-left: var(--space-sm);
@@ -345,125 +350,168 @@
   padding: var(--space-xl);
 }
 
-// Below this width the fixed-width rail would eat too much of the
-// viewport (relevant early given this app is meant to be embedded via
-// Capacitor later, see the root README) — collapse it into a horizontal
-// top bar instead of a side rail.
-//
-// The primary nav (Planning/Recettes/Liste de courses) must stay fully
-// legible and tappable at any width — it's the app's main navigation, not
-// optional chrome. Without `&__nav { min-width: 0 }` + `a { flex-shrink: 0
-// }` below, `&__settings`/`&__footer`'s own natural (non-shrinking) width
-// silently crushed it down to ~16px unlabeled slivers on a narrow phone
-// (measured on a 375px viewport) — invisible labels, no real tap target.
-// The fix: `__settings`/`__footer` collapse to icon-only instead (same
-// look as the desktop rail's `.collapsed` state), freeing width for the
-// nav, which falls back to horizontal scroll (`overflow-x: auto`) rather
-// than shrinking if it still doesn't fit.
-@media (max-width: 640px) {
-  .app-layout {
-    flex-direction: column;
-  }
-
-  // The desktop `var(--space-xl)` (32px) all around eats a big share of a
-  // ~375px screen — every page then has ~64px less usable width than the
-  // viewport already gives it. Drop to `--space-md` (16px) on phones; the
-  // grid/table pages that still overflow fall back to their own horizontal
-  // scroll (same philosophy as the sidebar below).
+// On a phone, `.app-sidebar` isn't rendered at all anymore (see
+// AppLayout.tsx) — replaced below by a fixed `.app-bottom-nav`, a genuinely
+// different component tree rather than the old approach of CSS-squashing
+// the same sidebar markup into a horizontal top bar. That old squashed bar
+// had no room left for Paramètres/Compte except as two separate floating
+// dropdowns with zero viewport-edge handling (see the mobile/tablet UI
+// chantier's own audit) — the bottom nav's single "Plus" tab + bottom sheet
+// replaces both.
+@include bp.phone {
   .app-content {
+    // The desktop `var(--space-xl)` (32px) all around eats a big share of a
+    // ~375px screen — every page then has ~64px less usable width than the
+    // viewport already gives it. Drop to `--space-md` (16px) on phones; the
+    // grid/table pages that still overflow fall back to their own
+    // horizontal scroll.
     padding: var(--space-md);
-  }
 
-  .app-sidebar {
-    flex-direction: row;
-    align-items: center;
-    width: 100%;
-    padding: var(--space-sm) var(--space-md);
-    border-right: none;
-    border-bottom: 1px solid var(--color-border);
-
-    &__top {
-      padding: 0 var(--space-sm) 0 0;
-    }
-
-    &__brand {
-      padding: 0;
-    }
-
-    // Nothing to collapse into on a horizontal bar — there's no rail.
-    &__collapse-toggle {
-      display: none;
-    }
-
-    // No room for this on a horizontal bar either.
-    &__version {
-      display: none;
-    }
-
-    &__nav {
-      flex: 1 1 auto;
-      min-width: 0;
-      flex-direction: row;
-      overflow-x: auto;
-
-      a {
-        flex-shrink: 0;
-      }
-    }
-
-    &__settings,
-    &__footer {
-      position: relative;
-      flex: none;
-      padding-top: 0;
-      border-top: none;
-    }
-
-    &__settings-toggle,
-    &__account-toggle {
-      padding-left: var(--space-xs);
-      padding-right: var(--space-xs);
-    }
-
-    &__settings-toggle-left .label,
-    &__account-toggle .label,
-    &__settings-toggle .chevron {
-      display: none;
-    }
-
-    // Both reveals become floating panels anchored under their icon-only
-    // toggle — on the desktop rail one is inline (settings, stacks fine in
-    // a column) and the other already floats (account); neither can stay
-    // in normal flow on this horizontal bar without breaking the row.
-    // Selector order matters: `&__settings-nav` also carries the plain
-    // `&__nav` class (for the link styling), so this must come after it to
-    // win on `flex-direction`/`overflow-x`.
-    &__settings-nav {
-      position: absolute;
-      top: calc(100% + var(--space-xs));
-      right: 0;
-      flex-direction: column;
-      width: 14rem;
-      padding: var(--space-xs);
-      overflow-x: visible;
-      background: var(--color-surface);
-      border: 1px solid var(--color-border);
-      border-radius: var(--radius-base);
-      box-shadow: var(--shadow-md);
-      z-index: 10;
-    }
-
-    // Desktop opens this *upward* (`bottom: calc(100% + ...)`, see the base
-    // rule above) because the footer sits at the bottom of a tall rail —
-    // on this horizontal top bar the footer is near `y: 0`, so "upward"
-    // pushed the menu entirely off-screen above the viewport. Flip it to
-    // open downward here instead.
-    &__account-menu {
-      top: calc(100% + var(--space-xs));
-      bottom: auto;
-      left: auto;
-      right: 0;
-      width: 12rem;
+    &--with-bottom-nav {
+      // Reserves space for the fixed `.app-bottom-nav` below (its own
+      // height + a little breathing room) so the last bit of scrollable
+      // content is never hidden behind it — `env(safe-area-inset-bottom)`
+      // additionally clears a phone's own gesture bar/rounded corners
+      // (falls back to `0px` on a browser that doesn't support `env()`,
+      // per the CSS spec's own fallback behavior for an unsupported
+      // environment variable inside `calc()`).
+      padding-bottom: calc(var(--space-md) + 3.5rem + env(safe-area-inset-bottom, 0px));
     }
   }
 }
+
+// --- Mobile bottom tab bar ------------------------------------------------
+// Only ever rendered on a phone (AppLayout.tsx gates it on
+// `useIsMobileViewport()`) — not wrapped in `@include bp.phone` itself
+// since there's no risk of it ever showing at a wider width with no JS
+// check at all, but its sizing still assumes a phone-width screen.
+.app-bottom-nav {
+  position: fixed;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  z-index: 10;
+  display: flex;
+  align-items: stretch;
+  height: calc(3.5rem + env(safe-area-inset-bottom, 0px));
+  padding-bottom: env(safe-area-inset-bottom, 0px);
+  background: var(--color-surface);
+  border-top: 1px solid var(--color-border);
+  box-shadow: var(--shadow-sm);
+
+  a,
+  &__more {
+    flex: 1;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    gap: 0.125rem;
+    border: none;
+    background: none;
+    color: var(--color-text-muted);
+    font-family: var(--font-body);
+    text-decoration: none;
+    cursor: pointer;
+
+    svg {
+      width: 1.375rem;
+      height: 1.375rem;
+    }
+
+    .label {
+      font-size: var(--font-size-xs);
+      font-weight: 600;
+    }
+
+    // Applied by NavLink itself (see AppLayout.tsx's `className` prop) for
+    // the 3 route tabs; `.app-bottom-nav__more` sets this manually via
+    // `aria-expanded` styling instead, since it opens a sheet rather than
+    // navigating to a route of its own.
+    &.active {
+      color: var(--color-primary);
+    }
+  }
+
+  &__more[aria-expanded="true"] {
+    color: var(--color-primary);
+  }
+}
+
+// --- Mobile "Plus" sheet content ------------------------------------------
+// Content of `MobileMoreSheet` (AppLayout.tsx) — reuses `BottomSheet`'s own
+// `.bottom-sheet__body` for scrolling/padding, these classes just style
+// what's inside it.
+.mobile-more-sheet__account {
+  display: flex;
+  align-items: center;
+  gap: var(--space-sm);
+  padding: var(--space-sm) 0 var(--space-md);
+  margin-bottom: var(--space-sm);
+  border-bottom: 1px solid var(--color-border);
+  font-weight: 600;
+}
+
+.mobile-more-sheet__avatar {
+  flex-shrink: 0;
+  width: 2rem;
+  height: 2rem;
+  display: grid;
+  place-items: center;
+  border-radius: 50%;
+  background: var(--color-primary);
+  color: #fff;
+  font-size: var(--font-size-sm);
+  font-weight: 700;
+}
+
+.mobile-more-sheet__nav {
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-xs);
+  margin-bottom: var(--space-md);
+
+  a {
+    display: flex;
+    align-items: center;
+    gap: var(--space-sm);
+    padding: var(--space-sm);
+    border-radius: var(--radius-base);
+    color: var(--color-text);
+    font-weight: 600;
+    font-size: var(--font-size-sm);
+    text-decoration: none;
+
+    svg {
+      flex-shrink: 0;
+      width: 1.25rem;
+      height: 1.25rem;
+    }
+
+    &:hover {
+      background: var(--color-surface-alt);
+    }
+
+    &.active {
+      background: var(--color-primary);
+      color: #fff;
+    }
+  }
+}
+
+.mobile-more-sheet__logout {
+  width: 100%;
+  padding: var(--space-sm);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-base);
+  background: none;
+  color: var(--color-error);
+  font-family: var(--font-body);
+  font-weight: 600;
+  font-size: var(--font-size-sm);
+  cursor: pointer;
+
+  &:hover {
+    background: var(--color-surface-alt);
+  }
+}
diff --git a/apps/web/src/layouts/AppLayout.tsx b/apps/web/src/layouts/AppLayout.tsx
index 861ff59..6199617 100644
--- a/apps/web/src/layouts/AppLayout.tsx
+++ b/apps/web/src/layouts/AppLayout.tsx
@@ -1,8 +1,10 @@
 import { useState } from "react";
 import { useTranslation } from "react-i18next";
 import { NavLink, Outlet, useLocation, useNavigate } from "react-router-dom";
+import { BottomSheet } from "../components/ui/BottomSheet";
 import { UpdateBanner } from "../features/app-update/UpdateBanner";
 import { useAuth } from "../features/auth/AuthContext";
+import { useIsMobileViewport } from "../lib/useIsMobileViewport";
 import "./AppLayout.scss";
 import {
   AccountIcon,
@@ -10,6 +12,7 @@ import {
   CreditsIcon,
   DietPreferencesIcon,
   HouseholdIcon,
+  MoreIcon,
   PlanningIcon,
   RecipesIcon,
   SettingsIcon,
@@ -17,13 +20,15 @@ import {
   UserPreferencesIcon,
 } from "./nav-icons";
 
-/** `localStorage` key persisting {@link AppLayout}'s collapsed/expanded sidebar state across reloads. */
+/** `localStorage` key persisting {@link AppLayout}'s collapsed/expanded sidebar state across reloads. Desktop-only — the mobile bottom nav has nothing to collapse. */
 const SIDEBAR_COLLAPSED_KEY = "batchcooking:sidebarCollapsed";
 
 /**
- * One entry in the sidebar's main nav. `key` maps to `layout.nav.<key>` in
+ * One entry in the app's main nav. `key` maps to `layout.nav.<key>` in
  * `locales/fr/translation.json` — adding a section is one array entry plus
- * one locale key, no other file to touch.
+ * one locale key, no other file to touch. Shared verbatim between the
+ * desktop sidebar and the mobile bottom tab bar (see {@link MobileBottomNav})
+ * — same items, same routing, just a different container.
  */
 const NAV_ITEMS = [
   { to: "/", key: "planning", Icon: PlanningIcon, tourTarget: "nav-planning" },
@@ -37,8 +42,9 @@ const NAV_ITEMS = [
 ] as const;
 
 /**
- * One entry in the "Paramètres" nav, revealed by {@link SettingsMenu}. `key`
- * maps to `layout.settings.nav.<key>`.
+ * One entry in the "Paramètres" nav — revealed by {@link SettingsMenu} on
+ * desktop, listed inside {@link MobileMoreSheet} on mobile. `key` maps to
+ * `layout.settings.nav.<key>`.
  */
 const SETTINGS_ITEMS = [
   { to: "/parametres/compte", key: "account", Icon: AccountIcon },
@@ -49,16 +55,28 @@ const SETTINGS_ITEMS = [
 ] as const;
 
 /**
- * Shell for every authenticated page: a sidebar (brand, section nav, a
- * collapsible "Paramètres" nav, and the account menu at the bottom) plus a
- * main content area rendering the matched child route via `<Outlet />`.
+ * Shell for every authenticated page: on desktop/tablet, a sidebar (brand,
+ * section nav, a collapsible "Paramètres" nav, and the account menu at the
+ * bottom); on a phone, a bottom tab bar instead (see {@link MobileBottomNav})
+ * — a genuinely different component tree, not a CSS-only reflow of the same
+ * one. Either way, a main content area renders the matched child route via
+ * `<Outlet />`.
  *
- * The sidebar itself can be collapsed to an icon-only rail (see
- * `isCollapsed`/`SIDEBAR_COLLAPSED_KEY`) — every nav item keeps its icon
- * and gains a `title` tooltip, its label just hides via CSS
+ * Which shell renders is decided once, here, via
+ * {@link useIsMobileViewport} — the mobile/tablet UI chantier's own audit
+ * found this app had *zero* precedent for branching actual markup by
+ * viewport before this component; every other consumer of that hook (the
+ * planning popovers, in a later ticket of the same chantier) should follow
+ * this same "check once at the shell/container level" pattern rather than
+ * re-checking deep inside a leaf component.
+ *
+ * The desktop sidebar itself can still be collapsed to an icon-only rail
+ * (see `isCollapsed`/`SIDEBAR_COLLAPSED_KEY`) — every nav item keeps its
+ * icon and gains a `title` tooltip, its label just hides via CSS
  * (`.app-sidebar.collapsed .label`, see AppLayout.scss), so collapsing is a
  * single class toggle on the `<aside>`, not something each child component
- * needs to know about.
+ * needs to know about. Nothing on the mobile bottom bar collapses — there's
+ * no room saved by doing so on an already-narrow screen.
  *
  * Mounted once as the parent element of the whole authenticated route
  * group, itself wrapped in {@link RequireAuth} (see `App.tsx`) — `user` is
@@ -66,6 +84,7 @@ const SETTINGS_ITEMS = [
  */
 export function AppLayout() {
   const { t } = useTranslation();
+  const isMobile = useIsMobileViewport();
   const [isCollapsed, setIsCollapsed] = useState(
     () => localStorage.getItem(SIDEBAR_COLLAPSED_KEY) === "true",
   );
@@ -80,64 +99,93 @@ export function AppLayout() {
 
   return (
     <div className="app-layout">
-      <aside className={isCollapsed ? "app-sidebar collapsed" : "app-sidebar"}>
-        <div className="app-sidebar__top">
-          <div className="app-sidebar__brand">
-            {/* Collapsed: a short monogram instead of the full wordmark — clearer than an arbitrary icon standing in for the brand itself. */}
-            <span className="app-sidebar__brand-full">batchCooking</span>
-            <span className="app-sidebar__brand-mark">bC</span>
-          </div>
-          <button
-            type="button"
-            className="app-sidebar__collapse-toggle"
-            onClick={toggleCollapsed}
-            title={t(isCollapsed ? "layout.sidebar.expand" : "layout.sidebar.collapse")}
-          >
-            <ChevronLeftIcon aria-hidden="true" />
-          </button>
-        </div>
-
-        <nav className="app-sidebar__nav">
-          {NAV_ITEMS.map(({ to, key, Icon, tourTarget }) => (
-            <NavLink
-              key={to}
-              to={to}
-              // Only the home ("/") entry needs exact matching — every
-              // other path is a leaf with nothing nested under it (yet),
-              // so NavLink's default prefix matching already behaves the
-              // same way `end` would.
-              end={to === "/"}
-              className={({ isActive }) => (isActive ? "active" : undefined)}
-              title={t(`layout.nav.${key}`)}
-              data-tour={tourTarget}
+      {!isMobile && (
+        <aside className={isCollapsed ? "app-sidebar collapsed" : "app-sidebar"}>
+          <div className="app-sidebar__top">
+            <div className="app-sidebar__brand">
+              {/* Collapsed: a short monogram instead of the full wordmark — clearer than an arbitrary icon standing in for the brand itself. */}
+              <span className="app-sidebar__brand-full">batchCooking</span>
+              <span className="app-sidebar__brand-mark">bC</span>
+            </div>
+            <button
+              type="button"
+              className="app-sidebar__collapse-toggle"
+              onClick={toggleCollapsed}
+              title={t(isCollapsed ? "layout.sidebar.expand" : "layout.sidebar.collapse")}
             >
-              <Icon aria-hidden="true" />
-              <span className="label">{t(`layout.nav.${key}`)}</span>
-            </NavLink>
-          ))}
-        </nav>
+              <ChevronLeftIcon aria-hidden="true" />
+            </button>
+          </div>
 
-        <SettingsMenu />
-        <AccountMenu />
-        <p className="app-sidebar__version" aria-hidden="true">
-          v{__APP_VERSION__}
-        </p>
-      </aside>
+          <nav className="app-sidebar__nav">
+            {NAV_ITEMS.map(({ to, key, Icon, tourTarget }) => (
+              <NavLink
+                key={to}
+                to={to}
+                // Only the home ("/") entry needs exact matching — every
+                // other path is a leaf with nothing nested under it (yet),
+                // so NavLink's default prefix matching already behaves the
+                // same way `end` would.
+                end={to === "/"}
+                className={({ isActive }) => (isActive ? "active" : undefined)}
+                title={t(`layout.nav.${key}`)}
+                data-tour={tourTarget}
+              >
+                <Icon aria-hidden="true" />
+                <span className="label">{t(`layout.nav.${key}`)}</span>
+              </NavLink>
+            ))}
+          </nav>
 
-      <main className="app-content">
+          <SettingsMenu />
+          <AccountMenu />
+          <p className="app-sidebar__version" aria-hidden="true">
+            v{__APP_VERSION__}
+          </p>
+        </aside>
+      )}
+
+      <main className={isMobile ? "app-content app-content--with-bottom-nav" : "app-content"}>
         {/* Renders nothing on the web build (native-only check) or once no
             newer version is known — see UpdateBanner's own doc comment. */}
         <UpdateBanner />
         <Outlet />
       </main>
+
+      {isMobile && <MobileBottomNav />}
     </div>
   );
 }
 
+/**
+ * Ends the session and returns to `/` — `RequireAuth` shows the public
+ * {@link LandingPage} there for a logged-out visitor (issue #41). Shared by
+ * {@link AccountMenu} (desktop dropdown) and {@link MobileMoreSheet}
+ * (mobile sheet) — both need the exact same behavior, only how they close
+ * their own menu/sheet beforehand differs, which is why this doesn't also
+ * take care of that step itself.
+ */
+function useLogout(): () => Promise<void> {
+  const { logout } = useAuth();
+  const navigate = useNavigate();
+  return async function handleLogout() {
+    try {
+      await logout();
+      void navigate("/");
+    } catch (err) {
+      // Rethrown as-is — `AuthContext`'s `logout` already documents itself
+      // as throwing `ApiError` on failure; this handler just isn't allowed
+      // a bare `await` per the repo's async/try-catch convention.
+      throw err;
+    }
+  };
+}
+
 /**
  * Collapsible "Paramètres" section revealing the settings pages (Compte /
  * Préférences alimentaires / Foyer / Préférences utilisateur — see
- * `pages/settings/`). Starts open whenever the current route is already
+ * `pages/settings/`). Desktop/tablet only — see {@link MobileMoreSheet} for
+ * the mobile equivalent. Starts open whenever the current route is already
  * under `/parametres`, so following a link there (e.g. from
  * {@link AccountMenu}) doesn't land on a collapsed menu; otherwise starts
  * closed to keep the sidebar's main focus on the primary nav above it.
@@ -193,29 +241,20 @@ function SettingsMenu() {
  * the very bottom of the sidebar, replacing what used to be a plain
  * greeting + logout button. Offers a shortcut straight to `/parametres/compte`
  * plus the logout action; closes itself after either action so it never
- * lingers open across a navigation.
+ * lingers open across a navigation. Desktop/tablet only — see
+ * {@link MobileMoreSheet} for the mobile equivalent.
  */
 function AccountMenu() {
-  const { user, logout } = useAuth();
-  const navigate = useNavigate();
+  const { user } = useAuth();
+  const handleLogout = useLogout();
   const { t } = useTranslation();
   const [isOpen, setIsOpen] = useState(false);
 
-  /**
-   * Ends the session and returns to `/` — `RequireAuth` shows the public
-   * {@link LandingPage} there for a logged-out visitor (issue #41), so this
-   * naturally lands on the marketing page rather than straight back at the
-   * login form.
-   */
-  async function handleLogout() {
+  async function onLogoutClick() {
     setIsOpen(false);
     try {
-      await logout();
-      void navigate("/");
+      await handleLogout();
     } catch (err) {
-      // Rethrown as-is — `AuthContext`'s `logout` already documents itself
-      // as throwing `ApiError` on failure; this handler just isn't allowed
-      // a bare `await` per the repo's async/try-catch convention.
       throw err;
     }
   }
@@ -242,7 +281,7 @@ function AccountMenu() {
           <NavLink to="/parametres/compte" onClick={() => setIsOpen(false)}>
             {t("layout.accountMenu.myAccount")}
           </NavLink>
-          <button type="button" onClick={handleLogout}>
+          <button type="button" onClick={() => void onLogoutClick()}>
             {t("layout.logout")}
           </button>
         </div>
@@ -250,3 +289,115 @@ function AccountMenu() {
     </div>
   );
 }
+
+/**
+ * Mobile shell's nav — a fixed bottom tab bar (the 3 {@link NAV_ITEMS},
+ * same as desktop) plus a 4th "Plus" tab opening {@link MobileMoreSheet}.
+ * Replaces the old ≤640px treatment (the desktop sidebar CSS-squashed into
+ * a horizontal scrolling top bar) — that approach had no room left for
+ * Paramètres/Compte except as two separate floating dropdowns with no
+ * viewport-edge handling at all (see the mobile/tablet UI chantier's own
+ * audit). A bottom tab bar is also the platform-conventional place for
+ * primary nav on both Android and iOS, unlike a top bar.
+ *
+ * Paramètres and Compte are deliberately combined into ONE "Plus" sheet
+ * rather than kept as two separate triggers (which is what the desktop
+ * sidebar still does) — simpler mobile IA, and avoids needing a second tab
+ * slot on an already-tight 4-tab bar.
+ */
+function MobileBottomNav() {
+  const { t } = useTranslation();
+  const [isMoreOpen, setIsMoreOpen] = useState(false);
+
+  return (
+    <>
+      <nav className="app-bottom-nav">
+        {NAV_ITEMS.map(({ to, key, Icon, tourTarget }) => (
+          <NavLink
+            key={to}
+            to={to}
+            end={to === "/"}
+            className={({ isActive }) => (isActive ? "active" : undefined)}
+            data-tour={tourTarget}
+          >
+            <Icon aria-hidden="true" />
+            <span className="label">{t(`layout.nav.${key}`)}</span>
+          </NavLink>
+        ))}
+        <button
+          type="button"
+          className="app-bottom-nav__more"
+          aria-haspopup="dialog"
+          aria-expanded={isMoreOpen}
+          onClick={() => setIsMoreOpen(true)}
+        >
+          <MoreIcon aria-hidden="true" />
+          <span className="label">{t("layout.nav.more")}</span>
+        </button>
+      </nav>
+
+      {isMoreOpen && <MobileMoreSheet onClose={() => setIsMoreOpen(false)} />}
+    </>
+  );
+}
+
+/**
+ * The mobile "Plus" tab's content — {@link BottomSheet} wrapping the same
+ * account greeting/logout and Paramètres links as the desktop
+ * {@link AccountMenu}/{@link SettingsMenu}, just laid out as one scrollable
+ * list instead of two separate dropdowns. Every link/button here calls
+ * `onClose` itself (in addition to whatever navigation/logout it triggers)
+ * — the same "the trigger closes its own menu" responsibility the desktop
+ * dropdowns already have, just routed through a prop here since this
+ * content is `BottomSheet`'s `children`, not code that shares a closure
+ * with the `<dialog>` ref.
+ */
+function MobileMoreSheet({ onClose }: { onClose: () => void }) {
+  const { t } = useTranslation();
+  const { user } = useAuth();
+  const handleLogout = useLogout();
+
+  async function onLogoutClick() {
+    onClose();
+    try {
+      await handleLogout();
+    } catch (err) {
+      throw err;
+    }
+  }
+
+  const initial = user?.firstName?.charAt(0).toUpperCase() ?? "";
+
+  return (
+    <BottomSheet onClose={onClose} title={t("layout.settings.toggle")}>
+      <div className="mobile-more-sheet__account">
+        <span className="mobile-more-sheet__avatar" aria-hidden="true">
+          {initial}
+        </span>
+        <span>{t("layout.greeting", { firstName: user?.firstName })}</span>
+      </div>
+
+      <nav className="mobile-more-sheet__nav">
+        {SETTINGS_ITEMS.map(({ to, key, Icon }) => (
+          <NavLink
+            key={to}
+            to={to}
+            onClick={onClose}
+            className={({ isActive }) => (isActive ? "active" : undefined)}
+          >
+            <Icon aria-hidden="true" />
+            <span>{t(`layout.settings.nav.${key}`)}</span>
+          </NavLink>
+        ))}
+      </nav>
+
+      <button
+        type="button"
+        className="mobile-more-sheet__logout"
+        onClick={() => void onLogoutClick()}
+      >
+        {t("layout.logout")}
+      </button>
+    </BottomSheet>
+  );
+}
diff --git a/apps/web/src/layouts/nav-icons.tsx b/apps/web/src/layouts/nav-icons.tsx
index dbfb6fb..6793608 100644
--- a/apps/web/src/layouts/nav-icons.tsx
+++ b/apps/web/src/layouts/nav-icons.tsx
@@ -21,6 +21,11 @@ export {
   Home as HouseholdIcon,
   Info as CreditsIcon,
   Leaf as DietPreferencesIcon,
+  // The mobile bottom nav's catch-all "Plus" tab (Paramètres + Compte,
+  // see AppLayout.tsx's `MobileBottomNav`) — a hamburger reads as "more"
+  // even in a bottom-tab position, unlike on desktop where it usually
+  // means "open a side drawer".
+  Menu as MoreIcon,
   Palette as UserPreferencesIcon,
   Rss as SourcesIcon,
   Settings as SettingsIcon,
diff --git a/apps/web/src/lib/useIsMobileViewport.ts b/apps/web/src/lib/useIsMobileViewport.ts
new file mode 100644
index 0000000..1561f54
--- /dev/null
+++ b/apps/web/src/lib/useIsMobileViewport.ts
@@ -0,0 +1,59 @@
+import { useEffect, useState } from "react";
+
+/**
+ * The one point of truth for "should a component render its mobile
+ * variant" — a live `window.matchMedia` check against the same phone
+ * threshold as `styles/_breakpoints.scss`'s `$phone` Sass variable (640px;
+ * the two can't literally share a value — Sass compiles away before this
+ * ever runs — so keep them in sync by hand if this ever changes).
+ *
+ * Before this hook, nothing in the repo branched actual JSX/markup by
+ * viewport width — every existing "responsive" adaptation was CSS-only on
+ * an identical DOM (see the mobile/tablet UI chantier's own audit). This is
+ * the first, and should stay the *only*, place that check lives; a
+ * component that needs a genuinely different structure on a phone (not
+ * just different styling) reads this hook rather than adding its own
+ * `matchMedia` call.
+ *
+ * Live, not a one-time read at mount: rotating a tablet, resizing a
+ * desktop browser window, or Chrome DevTools' device toolbar must all
+ * re-render the affected component, not just the very first paint.
+ */
+export function useIsMobileViewport(): boolean {
+  const [isMobile, setIsMobile] = useState(() => matchesPhoneQuery());
+
+  useEffect(() => {
+    const mediaQueryList = window.matchMedia(PHONE_MEDIA_QUERY);
+    // Older Safari only supports the deprecated `addListener`/
+    // `removeListener` pair, but this app's minimum target is a Capacitor
+    // Android WebView plus evergreen desktop browsers — `addEventListener`
+    // is safe here, no legacy fallback needed.
+    function handleChange(event: MediaQueryListEvent) {
+      setIsMobile(event.matches);
+    }
+    mediaQueryList.addEventListener("change", handleChange);
+    // The query itself can't change between mount and this effect running,
+    // but the viewport can (e.g. a window resize mid-render) — resync once
+    // on mount in case `useState`'s initializer already went stale.
+    setIsMobile(mediaQueryList.matches);
+    return () => mediaQueryList.removeEventListener("change", handleChange);
+  }, []);
+
+  return isMobile;
+}
+
+/** Must match `styles/_breakpoints.scss`'s `$phone` value exactly. */
+const PHONE_BREAKPOINT_PX = 640;
+const PHONE_MEDIA_QUERY = `(max-width: ${PHONE_BREAKPOINT_PX}px)`;
+
+/**
+ * Guards the `window` access this needs for `useState`'s lazy initializer —
+ * safe to call unconditionally in a browser/Capacitor WebView, but this
+ * hook is also imported by Cypress component-test bundles and (in theory) a
+ * future SSR pass, neither of which is guaranteed to run this in a real
+ * `window` context.
+ */
+function matchesPhoneQuery(): boolean {
+  if (typeof window === "undefined") return false;
+  return window.matchMedia(PHONE_MEDIA_QUERY).matches;
+}
diff --git a/apps/web/src/locales/fr/translation.json b/apps/web/src/locales/fr/translation.json
index 9468a1d..e9a7f57 100644
--- a/apps/web/src/locales/fr/translation.json
+++ b/apps/web/src/locales/fr/translation.json
@@ -106,7 +106,8 @@
     "nav": {
       "planning": "Planning",
       "recipes": "Recettes",
-      "shoppingList": "Liste de courses"
+      "shoppingList": "Liste de courses",
+      "more": "Plus"
     },
     "settings": {
       "toggle": "Paramètres",
diff --git a/apps/web/src/pages/admin/tours/tours-page.scss b/apps/web/src/pages/admin/tours/tours-page.scss
index 0bafb81..71a2eec 100644
--- a/apps/web/src/pages/admin/tours/tours-page.scss
+++ b/apps/web/src/pages/admin/tours/tours-page.scss
@@ -1,5 +1,10 @@
 // Admin tour-scenario CRUD (ToursPage). Colocated; the generic
 // `.admin-page__title` etc. come from ../admin-page.scss.
+//
+// The 860px hero-style collapse a little further down is deliberately its
+// own local value, not `bp.$tablet` — see landing-page.scss's identical
+// note on why that specific number isn't unified with the shared token.
+@use "../../../styles/breakpoints" as bp;
 
 .tours-page {
   .admin-page__header {
@@ -184,7 +189,7 @@
     grid-template-columns: 1fr 1fr;
     gap: var(--space-sm);
 
-    @media (max-width: 640px) {
+    @include bp.phone {
       grid-template-columns: 1fr;
     }
   }
diff --git a/apps/web/src/pages/landing/landing-page.scss b/apps/web/src/pages/landing/landing-page.scss
index befe47f..97ed857 100644
--- a/apps/web/src/pages/landing/landing-page.scss
+++ b/apps/web/src/pages/landing/landing-page.scss
@@ -1,8 +1,15 @@
 // LandingPage — the public page at `/` for a logged-out visitor. Colocated
 // with LandingPage.tsx. Every colour is a `var(--color-*)` token so it
 // resolves per-theme globally (styles/_theme.scss); no light/dark blocks
-// here. The `@media (max-width: 640px)` phone treatment follows the same
+// here. The phone treatment (`bp.phone` below) follows the same
 // "stack, don't cram" philosophy as the rest of the app (AppLayout.scss).
+//
+// The hero grid's own 860px collapse just below is deliberately its own
+// local value, not `bp.$tablet` (1024px) — a 2-column hero collapsing at
+// exactly the same width as the recipe catalog's master-detail split would
+// be a coincidence, not a real shared concept; forcing it onto that token
+// would shift this specific breakpoint and change real layout behavior.
+@use "../../styles/breakpoints" as bp;
 
 .landing {
   max-width: 68rem;
@@ -21,7 +28,7 @@
     margin-top: var(--space-2xl);
   }
 
-  @media (max-width: 640px) {
+  @include bp.phone {
     padding: var(--space-lg) var(--space-md) var(--space-xl);
 
     section + section {
@@ -54,7 +61,7 @@
   margin: 0 0 var(--space-md);
   font-size: calc(var(--font-size-xl) * 1.5);
 
-  @media (max-width: 640px) {
+  @include bp.phone {
     font-size: var(--font-size-xl);
   }
 }
diff --git a/apps/web/src/pages/planning/planning-page.scss b/apps/web/src/pages/planning/planning-page.scss
index 82a633a..af40575 100644
--- a/apps/web/src/pages/planning/planning-page.scss
+++ b/apps/web/src/pages/planning/planning-page.scss
@@ -7,6 +7,8 @@
 // styles/_theme.scss).
 // =============================================================================
 
+@use "../../styles/breakpoints" as bp;
+
 // `.app-content` (AppLayout.scss) already stretches to the full viewport
 // height (flex item of `.app-layout`, itself `min-height: 100vh` — the
 // same stretch the sidebar relies on to pin its footer at the bottom).
@@ -272,7 +274,7 @@ table.planning-grid {
 // illegibility (same philosophy as the sidebar's own fallback). What does
 // NOT survive the switch to touch are the two hover-gated affordances
 // below.
-@media (max-width: 640px) {
+@include bp.phone {
   // `.recipe-chip__remove` sits at `opacity: 0` until its chip is hovered
   // — invisible, and untappable, on a touch screen where nothing is ever
   // "hovered". Pin it visible so a planned recipe can actually be removed
diff --git a/apps/web/src/styles/_breakpoints.scss b/apps/web/src/styles/_breakpoints.scss
new file mode 100644
index 0000000..a751a81
--- /dev/null
+++ b/apps/web/src/styles/_breakpoints.scss
@@ -0,0 +1,49 @@
+// =============================================================================
+// Named breakpoints — the single source of truth for "phone" vs "tablet" vs
+// "desktop" width thresholds, replacing the 640/860/1024px magic numbers
+// that used to be copy-pasted independently into AppLayout.scss,
+// landing-page.scss, recipes.scss, recipe-picker-dialog.scss,
+// planning-page.scss, dialog.scss and tours-page.scss.
+//
+// Plain Sass variables + mixins, NOT CSS custom properties on :root like the
+// rest of the design tokens in `_theme.scss` — a `@media` condition can't
+// read a `var(--…)` (custom properties resolve at computed-value time, a
+// media query is evaluated before that even exists), so a breakpoint has to
+// be a compile-time value. `@use` this partial wherever a `@media` rule
+// needs one of these; never repeat the raw pixel value.
+//
+// `useIsMobileViewport()` (apps/web/src/hooks/useIsMobileViewport.ts) needs
+// the exact same "phone" threshold for its own `matchMedia` runtime check —
+// TS can't import a Sass variable, so that hook hardcodes the same 640
+// number with a comment pointing back here. Keep both in sync by hand if
+// this ever changes; there are only the two places.
+// =============================================================================
+
+$phone: 640px;
+$tablet: 1024px;
+
+/// Styles that apply at phone width and below (≤ $phone).
+@mixin phone {
+  @media (max-width: $phone) {
+    @content;
+  }
+}
+
+/// Styles that apply above phone width (> $phone) — the exact complement of
+/// `phone` above, for a rule that must never double-apply with it (see
+/// AppLayout.scss's `.collapsed` rail, which relies on this not overlapping
+/// the mobile bottom-bar rules at all).
+@mixin phone-up {
+  @media (min-width: $phone + 1) {
+    @content;
+  }
+}
+
+/// Styles that apply at tablet width and below (≤ $tablet) — i.e. "narrower
+/// than a full desktop layout", used for e.g. collapsing a two-column
+/// master-detail split into one column.
+@mixin tablet-down {
+  @media (max-width: $tablet) {
+    @content;
+  }
+}