filter: blocklist downloads never reuse a pooled connection, the peer closes it between passes

src/app.zig

@@ -482,7 +482,19 @@ fn serve(r: cli.Runner, args: cli.RunArgs) !u8 {
     // Two HTTP clients on purpose. A blocklist download streams tens of
     // megabytes and holds its connection for the whole of it; DoH queries must
     // not queue behind that, and the two have nothing to share but a type.
-    var fetch_http: std.http.Client = .{ .allocator = gpa, .io = io };
+    // `free_size = 0` makes `release` destroy every connection and the pool
+    // hand none back (`Client.zig:133`). The fetcher's `.keep_alive = false` is
+    // what sends `connection: close`, but it cannot carry this alone: `request`
+    // takes a pooled connection before it stores the flag (`Client.zig:1725`,
+    // `:1742`), and a failed send leaves a `.ready` connection that
+    // `Request.deinit` would pool (`Client.zig:890`). A pass runs once a day,
+    // so any kept connection is closed at the peer by the next one, and the
+    // client never retries a stale one — it fails the source for the day.
+    var fetch_http: std.http.Client = .{
+        .allocator = gpa,
+        .io = io,
+        .connection_pool = .{ .free_size = 0 },
+    };
     defer fetch_http.deinit();
     var dns_http: std.http.Client = .{ .allocator = gpa, .io = io };
     defer dns_http.deinit();