fix(astro): do not open new tab when saving config files

.changeset/proud-singers-call.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes `astro dev --open` unexpected behavior that spawns a new tab every time a config file is saved

packages/astro/src/core/dev/container.ts

@@ -56,9 +56,23 @@ export async function createContainer({
 		base,
 		server: { host, headers, open: serverOpen },
 	} = settings.config;
+
+	// serverOpen = true, isRestart = false
+	// when astro dev --open command is run the first time
+	// expected behavior: spawn a new tab
+	// ------------------------------------------------------
+	// serverOpen = true, isRestart = true
+	// when config file is saved
+	// expected behavior: do not spawn a new tab
+	// ------------------------------------------------------
+	// Non-config files don't reach this point
+	const isServerOpenURL = typeof serverOpen == 'string' && !isRestart;
+	const isServerOpenBoolean = serverOpen && !isRestart;
+
 	// Open server to the correct path. We pass the `base` here as we didn't pass the
 	// base to the initial Vite config
-	const open = typeof serverOpen == 'string' ? serverOpen : serverOpen ? base : false;
+	const open = isServerOpenURL ? serverOpen
+		: isServerOpenBoolean ? base : false;
 
 	// The client entrypoint for renderers. Since these are imported dynamically
 	// we need to tell Vite to preoptimize them.