diff --git a/backend/src/api/chapters.rs b/backend/src/api/chapters.rs
index 6a514de..de01895 100644
--- a/backend/src/api/chapters.rs
+++ b/backend/src/api/chapters.rs
@@ -69,6 +69,21 @@ async fn get_one(
     Ok(Json(chapter))
 }
 
+/// Add a chapter to a manga.
+///
+/// **Authorization is intentionally open**: any authenticated principal —
+/// a browser session *or* a bot API token — may add a chapter to *any*
+/// manga, including crawler-imported rows. This is by design: chapters are
+/// treated as community contributions, unlike the manga record itself
+/// (title/cover/metadata), whose edits gate through `require_can_edit`
+/// (see [`crate::api::mangas`]). The `CurrentUser` binding still requires a
+/// valid identity, so contributions are attributable, just not owner-scoped.
+///
+/// This contract is locked by `tests/api_chapters.rs`
+/// (`non_owner_can_upload_chapter`); changing it to owner-only is a
+/// deliberate decision, not a drive-by tightening. Until a richer
+/// contributor/moderation model lands this is acknowledged, intended
+/// behaviour — see the auth note in CLAUDE.md.
 async fn create(
     State(state): State<AppState>,
     CurrentUser(user): CurrentUser,
diff --git a/backend/tests/api_chapters.rs b/backend/tests/api_chapters.rs
index 4b7b978..6267b8e 100644
--- a/backend/tests/api_chapters.rs
+++ b/backend/tests/api_chapters.rs
@@ -8,6 +8,8 @@ use uuid::Uuid;
 #[allow(unused_imports)]
 use serde_json as _;
 
+use common::MultipartBuilder;
+
 async fn seed_manga(h: &common::Harness, cookie: &str, title: &str) -> Uuid {
     common::seed_manga_via_api(&h.app, cookie, title).await
 }
@@ -272,3 +274,44 @@ async fn list_pages_returns_404_for_unknown_chapter(pool: PgPool) {
         .unwrap();
     assert_eq!(resp.status(), StatusCode::NOT_FOUND);
 }
+
+#[sqlx::test(migrations = "./migrations")]
+async fn non_owner_can_upload_chapter(pool: PgPool) {
+    // Contract lock: chapter upload is INTENTIONALLY open to any
+    // authenticated user, not just the manga's creator. A user who did not
+    // create the manga can still contribute a chapter (community
+    // contributions), unlike manga-record edits which gate on ownership.
+    // If this ever needs to become owner-only, that's a deliberate change —
+    // this test (and the doc comment on `api::chapters::create`) should be
+    // updated together, not silently broken.
+    let h = common::harness(pool);
+
+    // Owner creates the manga.
+    let (_owner, owner_cookie) = common::register_user(&h.app).await;
+    let manga_id = seed_manga(&h, &owner_cookie, "Berserk").await;
+
+    // A different, non-owner user uploads a chapter to it.
+    let (_other, other_cookie) = common::register_user(&h.app).await;
+    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": 1, "title": "Contributed" }))
+                .add_file("page", "1.png", "image/png", &common::fake_png_bytes()),
+            &other_cookie,
+        ))
+        .await
+        .unwrap();
+
+    assert_eq!(
+        resp.status(),
+        StatusCode::CREATED,
+        "a non-owner authenticated user must be able to upload a chapter"
+    );
+    let body = common::body_json(resp).await;
+    assert_eq!(body["number"], 1);
+    assert_eq!(body["title"], "Contributed");
+    assert_eq!(body["page_count"], 1);
+}