fix double free in listen host variable

src/Config.zig

@@ -71,7 +71,7 @@ pub fn load(allocator: std.mem.Allocator, env: *const std.process.Environ.Map) !
     defer allocator.free(default_cache_dir);
 
     return .{
-        .listen_host = env.get("WTTR_LISTEN_HOST") orelse try allocator.dupe(u8, "0.0.0.0"),
+        .listen_host = try allocator.dupe(u8, env.get("WTTR_LISTEN_HOST") orelse "0.0.0.0"),
         .listen_port = if (env.get("WTTR_LISTEN_PORT")) |p|
             try std.fmt.parseInt(u16, p, 10)
         else
@@ -181,3 +181,19 @@ test "config loads defaults" {
     try std.testing.expectEqual(@as(u16, 8002), cfg.listen_port);
     try std.testing.expectEqual(@as(usize, 10_000), cfg.cache_size);
 }
+
+test "config owns WTTR_LISTEN_HOST independently of the environment map" {
+    const allocator = std.testing.allocator;
+    var env: std.process.Environ.Map = .init(allocator);
+    // Declared first so it runs last, matching `main`: the config is torn down
+    // while the environment map is still alive, then the map frees its values.
+    // A config that borrowed the map's string would free it twice.
+    defer env.deinit();
+    try env.put("WTTR_CACHE_DIR", @import("build_options").cache_dir);
+    try env.put("WTTR_LISTEN_HOST", "127.0.0.1");
+
+    const cfg = try Config.load(allocator, &env);
+    defer cfg.deinit(allocator);
+
+    try std.testing.expectEqualStrings("127.0.0.1", cfg.listen_host);
+}