diff --git a/docs/contributing/setup-manifest.md b/docs/contributing/setup-manifest.md
index f31955d62c..9f8863f82e 100644
--- a/docs/contributing/setup-manifest.md
+++ b/docs/contributing/setup-manifest.md
@@ -80,13 +80,17 @@ This project uses the following resources:
     `PACKAGE_APP_BASE_URL` is set without `APP_BASE_URL` rather than publishing
     a partial set. Any domain attached out-of-band must be added here before the
     next deploy, or that deploy will remove it.
-  - The route deliberately does **not** live in
-    `packages/worker/wrangler.jsonc`: `npm run dev` runs `wrangler dev` against
-    the **production** environment, and Wrangler resolves local request URLs
-    against the first configured route, so a committed route makes every local
-    request arrive as `http://kodyapps.dev/...` — canonical URLs, OAuth resource
-    metadata, and login redirects then point at the production domain from
-    localhost.
+  - Publishing routes also flips `workers_dev` to `false`, which silently drops
+    the `<name>.<subdomain>.workers.dev` trigger (Cloudflare then answers that
+    hostname with error 1042). The generator sets `workers_dev: true` alongside
+    the routes so that backup access path — which MCP clients may point at, and
+    which the deploy's URL fallback looks for — survives.
+  - The routes deliberately do **not** live in `packages/worker/wrangler.jsonc`:
+    `npm run dev` runs `wrangler dev` against the **production** environment,
+    and Wrangler resolves local request URLs against the first configured route,
+    so a committed route makes every local request arrive as
+    `http://kodyapps.dev/...` — canonical URLs, OAuth resource metadata, and
+    login redirects then point at the production domain from localhost.
   - The app origin (`heykody.dev`) stays attached out-of-band; Wrangler does not
     remove routes that the config omits.
   - Attaching a custom domain needs a deploy token with edit access to the
diff --git a/tools/ci/resource-utils.node.test.ts b/tools/ci/resource-utils.node.test.ts
index c87dbf5936..9240016646 100644
--- a/tools/ci/resource-utils.node.test.ts
+++ b/tools/ci/resource-utils.node.test.ts
@@ -68,6 +68,7 @@ test('writeGeneratedWranglerConfig preserves migrations and copies environment a
 					assets?: { run_worker_first?: Array<string> }
 					r2_buckets?: Array<{ binding: string; bucket_name: string }>
 					routes?: Array<{ pattern: string; custom_domain?: boolean }>
+					workers_dev?: boolean
 					vars?: Record<string, unknown>
 				}
 			}
@@ -114,6 +115,8 @@ test('writeGeneratedWranglerConfig preserves migrations and copies environment a
 				custom_domain: true,
 			},
 		])
+		// Publishing routes otherwise drops the workers.dev trigger.
+		expect(productionConfig.env?.production?.workers_dev).toBe(true)
 
 		const previewOutPath = path.join(tempDir, 'wrangler-preview.generated.json')
 		await writeGeneratedWranglerConfig({
@@ -150,8 +153,9 @@ test('writeGeneratedWranglerConfig preserves migrations and copies environment a
 			{ binding: 'EMAIL_BLOBS', bucket_name: 'kody-pr-123-email-blobs' },
 		])
 		// Preview serves package apps inline on its own origin, so it publishes no
-		// routes and keeps whatever domains are attached out-of-band.
+		// routes and keeps whatever domains and triggers it already had.
 		expect(previewConfig.env?.preview?.routes).toBeUndefined()
+		expect(previewConfig.env?.preview?.workers_dev).toBeUndefined()
 		expect(consoleError).toHaveBeenCalledWith(
 			`Wrote generated Wrangler config: ${previewOutPath}`,
 		)
diff --git a/tools/ci/resource-utils.ts b/tools/ci/resource-utils.ts
index f52e415270..5daed3a560 100644
--- a/tools/ci/resource-utils.ts
+++ b/tools/ci/resource-utils.ts
@@ -765,8 +765,13 @@ function addPackageAppCustomDomainRoute(input: {
 			.filter((hostname) => !routedHostnames.has(hostname))
 			.map((pattern) => ({ pattern, custom_domain: true })),
 	]
+	// Publishing routes flips `workers_dev` to false, which removed the
+	// `<name>.<subdomain>.workers.dev` trigger the deploy previously kept as a
+	// backup access path (and that MCP clients may be pointed at). Ask for it
+	// explicitly so adding a custom domain does not silently take it away.
+	input.targetEnv.workers_dev = true
 	console.error(
-		`Custom domain routes: ${appHostname} (APP_BASE_URL), ${packageAppHostname} (PACKAGE_APP_BASE_URL)`,
+		`Custom domain routes: ${appHostname} (APP_BASE_URL), ${packageAppHostname} (PACKAGE_APP_BASE_URL); workers.dev trigger kept`,
 	)
 }