fix: preserve source locale when duplicating content

duplicate() built the copy's slug against the source row's locale but
inserted the row without one, so create()'s fallback landed every copy
in 'en'. On locale-scoped admin lists the copy silently vanished, and
the mis-scoped slug-uniqueness check could trip the UNIQUE(slug, locale)
constraint when the generated slug already existed in 'en'.

Pass the source locale through to create(). Duplicates keep their own
fresh translation group — a copy is a new entry, not a translation —
which create() already does by default; a test now locks that in.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017m3BaSx6e1DQcU77hBLTxU

Author: edrpls

.changeset/duplicate-preserves-locale.md

@@ -0,0 +1,5 @@
+---
+"emdash": patch
+---
+
+Fixes the Duplicate action creating the copy in the default locale instead of the source entry's locale. Duplicates of non-English entries now stay in their locale — so they appear in the locale-filtered admin list they were duplicated from — and no longer fail with a unique-constraint error when the generated slug already exists in the default locale.

packages/core/src/database/repositories/content.ts

@@ -322,6 +322,7 @@ export class ContentRepository {
 			data: newData,
 			status: "draft",
 			authorId: authorId || original.authorId || undefined,
+			locale: original.locale ?? undefined,
 		});
 	}
 

packages/core/tests/integration/i18n/i18n.test.ts

@@ -189,6 +189,53 @@ describe("i18n (Integration)", () => {
 			).rejects.toThrow();
 		});
 
+		// ── duplicate ─────────────────────────────────────────────────
+
+		it("duplicate() preserves the source item's locale", async () => {
+			const original = await repo.create(
+				createPostFixture({ slug: "hola-mundo", locale: "es", data: { title: "Hola Mundo" } }),
+			);
+
+			const copy = await repo.duplicate("post", original.id);
+
+			expect(copy.locale).toBe("es");
+		});
+
+		it("duplicate() assigns a fresh translation group", async () => {
+			const enPost = await repo.create(createPostFixture({ slug: "hello", locale: "en" }));
+			const esPost = await repo.create(
+				createPostFixture({
+					slug: "hola",
+					locale: "es",
+					translationOf: enPost.id,
+					data: { title: "Hola" },
+				}),
+			);
+
+			const copy = await repo.duplicate("post", esPost.id);
+
+			expect(copy.translationGroup).toBe(copy.id);
+			expect(copy.translationGroup).not.toBe(esPost.translationGroup);
+		});
+
+		it("duplicate() does not collide with the generated slug in another locale", async () => {
+			await repo.create(
+				createPostFixture({
+					slug: "hola-mundo-copy",
+					locale: "en",
+					data: { title: "Unrelated EN Post" },
+				}),
+			);
+			const original = await repo.create(
+				createPostFixture({ slug: "hola-mundo", locale: "es", data: { title: "Hola Mundo" } }),
+			);
+
+			const copy = await repo.duplicate("post", original.id);
+
+			expect(copy.locale).toBe("es");
+			expect(copy.slug).toBe("hola-mundo-copy");
+		});
+
 		// ── findBySlug ────────────────────────────────────────────────
 
 		it("findBySlug() without locale returns any match", async () => {