diff --git a/backend/.dockerignore b/backend/.dockerignore
new file mode 100644
index 0000000..308fe72
--- /dev/null
+++ b/backend/.dockerignore
@@ -0,0 +1,10 @@
+# Shrink the build context the daemon ships to Docker — without this,
+# the multi-GB `target/` from a local `cargo build` would be uploaded
+# on every `docker compose build`.
+
+target/
+.sqlx/
+tests/
+*.md
+.env
+.env.*
diff --git a/backend/Cargo.lock b/backend/Cargo.lock
index 322bc77..fc32685 100644
--- a/backend/Cargo.lock
+++ b/backend/Cargo.lock
@@ -1033,7 +1033,7 @@ checksum = "5e5032e24019045c762d3c0f28f5b6b8bbf38563a65908389bf7978758920897"
 
 [[package]]
 name = "mangalord"
-version = "0.10.1"
+version = "0.10.2"
 dependencies = [
  "anyhow",
  "argon2",
diff --git a/backend/Cargo.toml b/backend/Cargo.toml
index 2da469c..91ad53b 100644
--- a/backend/Cargo.toml
+++ b/backend/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.10.1"
+version = "0.10.2"
 edition = "2021"
 
 [lib]
diff --git a/backend/Dockerfile b/backend/Dockerfile
index ebf2c21..68b7892 100644
--- a/backend/Dockerfile
+++ b/backend/Dockerfile
@@ -5,15 +5,18 @@ RUN apt-get update \
  && apt-get install -y --no-install-recommends pkg-config libssl-dev ca-certificates \
  && rm -rf /var/lib/apt/lists/*
 
-# Cache deps separately from sources.
-COPY Cargo.toml ./
+# Cache deps separately from sources. `--locked` makes cargo refuse to
+# update the lockfile, so the production image is built against the
+# exact crate versions CI tested. Without Cargo.lock + the flag, cargo
+# would silently resolve fresh on every image build.
+COPY Cargo.toml Cargo.lock ./
 RUN mkdir src && echo "fn main() {}" > src/main.rs && echo "" > src/lib.rs \
- && cargo build --release \
+ && cargo build --locked --release \
  && rm -rf src
 
 COPY src ./src
 COPY migrations ./migrations
-RUN touch src/main.rs src/lib.rs && cargo build --release
+RUN touch src/main.rs src/lib.rs && cargo build --locked --release
 
 FROM debian:bookworm-slim
 RUN apt-get update \
diff --git a/backend/src/api/chapters.rs b/backend/src/api/chapters.rs
index 4778c58..2026363 100644
--- a/backend/src/api/chapters.rs
+++ b/backend/src/api/chapters.rs
@@ -105,6 +105,15 @@ async fn create(
         message: "metadata part is required".into(),
         details: json!({ "metadata": "required" }),
     })?;
+    // Chapter number is 1-indexed everywhere (URLs, upload form,
+    // reader). Reject 0 / negative numbers up front so the row never
+    // makes it into the DB. Mirrors the page>=1 rule on bookmarks.
+    if metadata.number < 1 {
+        return Err(AppError::ValidationFailed {
+            message: "chapter number must be 1 or greater".into(),
+            details: json!({ "number": "must be >= 1" }),
+        });
+    }
     if pages.is_empty() {
         return Err(AppError::ValidationFailed {
             message: "at least one page is required".into(),
diff --git a/backend/tests/api_uploads.rs b/backend/tests/api_uploads.rs
index 385bc62..aabfddc 100644
--- a/backend/tests/api_uploads.rs
+++ b/backend/tests/api_uploads.rs
@@ -242,6 +242,36 @@ async fn create_chapter_with_pages_stores_each(pool: PgPool) {
     }
 }
 
+#[sqlx::test(migrations = "./migrations")]
+async fn create_chapter_rejects_non_positive_number_with_422(pool: PgPool) {
+    let h = common::harness(pool);
+    let (_, cookie) = common::register_user(&h.app).await;
+    let manga_id = common::seed_manga_via_api(&h.app, &cookie, "Berserk").await;
+
+    for bad_number in [0i32, -1, -100] {
+        let resp = h
+            .app
+            .clone()
+            .oneshot(common::post_multipart_with_cookie(
+                &format!("/api/v1/mangas/{manga_id}/chapters"),
+                MultipartBuilder::new()
+                    .add_json("metadata", json!({ "number": bad_number }))
+                    .add_file("page", "1.png", "image/png", &common::fake_png_bytes()),
+                &cookie,
+            ))
+            .await
+            .unwrap();
+        assert_eq!(
+            resp.status(),
+            StatusCode::UNPROCESSABLE_ENTITY,
+            "number={bad_number} should be rejected"
+        );
+        let body = common::body_json(resp).await;
+        assert_eq!(body["error"]["code"], "validation_failed");
+        assert!(body["error"]["details"]["number"].is_string());
+    }
+}
+
 #[sqlx::test(migrations = "./migrations")]
 async fn create_chapter_rejects_when_no_pages_with_422(pool: PgPool) {
     let h = common::harness(pool);
diff --git a/frontend/.dockerignore b/frontend/.dockerignore
new file mode 100644
index 0000000..1b0358e
--- /dev/null
+++ b/frontend/.dockerignore
@@ -0,0 +1,13 @@
+# Shrink the build context the daemon ships to Docker. node_modules in
+# particular would otherwise be re-uploaded on every build despite the
+# Dockerfile re-installing it from scratch inside the builder.
+
+node_modules/
+build/
+.svelte-kit/
+e2e/
+test-results/
+playwright-report/
+*.md
+.env
+.env.*
diff --git a/frontend/package.json b/frontend/package.json
index e8c2653..806924c 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.10.1",
+  "version": "0.10.2",
   "private": true,
   "type": "module",
   "scripts": {
diff --git a/frontend/src/routes/bookmarks/+page.svelte b/frontend/src/routes/bookmarks/+page.svelte
index 150638f..c0b2612 100644
--- a/frontend/src/routes/bookmarks/+page.svelte
+++ b/frontend/src/routes/bookmarks/+page.svelte
@@ -2,6 +2,7 @@
     let { data } = $props();
     const authenticated = $derived(data.authenticated);
     const bookmarks = $derived(data.bookmarks);
+    const error = $derived(data.error);
 </script>
 
 <svelte:head>
@@ -10,7 +11,11 @@
 
 <h1>Bookmarks</h1>
 
-{#if !authenticated}
+{#if error}
+    <p role="alert" data-testid="bookmarks-error">
+        Couldn't load bookmarks: {error}
+    </p>
+{:else if !authenticated}
     <p data-testid="bookmarks-signin">
         <a href="/login">Sign in</a> to see your bookmarks.
     </p>
diff --git a/frontend/src/routes/bookmarks/+page.ts b/frontend/src/routes/bookmarks/+page.ts
index dc7a694..bd431ed 100644
--- a/frontend/src/routes/bookmarks/+page.ts
+++ b/frontend/src/routes/bookmarks/+page.ts
@@ -7,10 +7,18 @@ export const ssr = false;
 export const load: PageLoad = async () => {
     try {
         const page = await listMyBookmarks();
-        return { bookmarks: page.items, authenticated: true };
+        return { bookmarks: page.items, authenticated: true, error: null };
     } catch (e) {
         if (e instanceof ApiError && e.status === 401) {
-            return { bookmarks: [], authenticated: false };
+            return { bookmarks: [], authenticated: false, error: null };
+        }
+        // Anything else (502 upstream_unavailable from a backend
+        // restart, 500 internal_error) is rendered inline rather than
+        // re-thrown — SvelteKit's generic error.html is not the right
+        // UX for a transient API blip and the user is already
+        // authenticated as far as we know.
+        if (e instanceof ApiError) {
+            return { bookmarks: [], authenticated: true, error: e.message };
         }
         throw e;
     }
diff --git a/frontend/src/routes/manga/[id]/chapter/[n]/+page.svelte b/frontend/src/routes/manga/[id]/chapter/[n]/+page.svelte
index 33d643e..8a7de67 100644
--- a/frontend/src/routes/manga/[id]/chapter/[n]/+page.svelte
+++ b/frontend/src/routes/manga/[id]/chapter/[n]/+page.svelte
@@ -32,10 +32,14 @@
         // Don't hijack keys while the user is typing in an input.
         const target = e.target as HTMLElement | null;
         if (target && (target.tagName === 'INPUT' || target.tagName === 'TEXTAREA')) return;
+        // Space is deliberately *not* bound — on viewports where a page
+        // image overflows (portrait phones, narrow desktop windows),
+        // users expect Space to scroll the page, and stealing it for
+        // next-page would skip past unread content. ArrowRight + j
+        // are the discoverable bindings.
         switch (e.key) {
             case 'ArrowRight':
             case 'j':
-            case ' ':
                 e.preventDefault();
                 next();
                 break;