fix(core): let sites override the collection sitemap route

.changeset/sitemap-collection-route-override.md

@@ -0,0 +1,5 @@
+---
+"emdash": patch
+---
+
+Skips the default `/sitemap-[collection].xml` route injection when the host site defines its own, matching the existing behaviour for `robots.txt` and `sitemap.xml`.

packages/core/src/astro/integration/routes.ts

@@ -842,10 +842,12 @@ export function injectCoreRoutes(
 		});
 	}
 
-	injectRoute({
-		pattern: "/sitemap-[collection].xml",
-		entrypoint: resolveRoute("sitemap-[collection].xml.ts"),
-	});
+	if (!options.srcDir || !hasUserDefinedPublicRoute(options.srcDir, "sitemap-[collection].xml")) {
+		injectRoute({
+			pattern: "/sitemap-[collection].xml",
+			entrypoint: resolveRoute("sitemap-[collection].xml.ts"),
+		});
+	}
 
 	if (!options.srcDir || !hasUserDefinedPublicRoute(options.srcDir, "robots.txt")) {
 		injectRoute({

packages/core/tests/unit/astro/routes.test.ts

@@ -111,6 +111,21 @@ describe("core media route injection", () => {
 		);
 	});
 
+	it("skips the collection sitemap route when the site defines its own", async () => {
+		await withTempSrcDir(
+			{
+				"pages/sitemap-[collection].xml.ts": "export const GET = () => new Response('');",
+			},
+			(srcDir) => {
+				const routes = collectRoutePatterns(srcDir);
+
+				expect(routes).not.toContain("/sitemap-[collection].xml");
+				expect(routes).toContain("/sitemap.xml");
+				expect(routes).toContain("/robots.txt");
+			},
+		);
+	});
+
 	it("detects index route files for root public route overrides", async () => {
 		await withTempSrcDir(
 			{