upstream: a diagnostics episode follows health, and a peer fault carries its cause

src/cli.zig

@@ -978,14 +978,14 @@ fn probeUpstreams(r: Runner, cfg: model.Config) !usize {
         // what keeps the close off `dot` while it is still undefined.
         var dot_wired = false;
         defer if (dot_wired) dot.close(r.io);
-        const client: transport.Client = switch (endpoint.scheme) {
+        const client: transport.Leaf = switch (endpoint.scheme) {
             .doh => doh: {
                 doh = doh_client.DohClient.init(&http, endpoint, &request_buf, &transfer_buf) catch {
                     try r.out.print("FAIL upstreams[{d}] {f}: not a usable DoH url\n", .{ i, safe_url.redactQuoted(server.url) });
                     failures += 1;
                     continue;
                 };
-                break :doh doh.client();
+                break :doh doh.leaf();
             },
             .dot => dot: {
                 dot = dot_client.DotClient.init(endpoint, server.tls_name, r.gpa, &bundle, &bundle_lock, null, .{
@@ -995,7 +995,7 @@ fn probeUpstreams(r: Runner, cfg: model.Config) !usize {
                     .stream_write = tls_buffers[3 * chunk ..],
                 });
                 dot_wired = true;
-                break :dot dot.client();
+                break :dot dot.leaf();
             },
         };
 
@@ -1792,8 +1792,8 @@ test "a failed DoT probe reaches close through the per-iteration defer without a
 
     try testing.expectEqual(@as(usize, 2), try probeUpstreams(r, cfg));
     try testing.expectEqualStrings(
-        "FAIL upstreams[0] 'tls://dns.example:853': ConnectFailed\n" ++
-            "FAIL upstreams[1] 'tls://other.example:853': ConnectFailed\n",
+        "FAIL upstreams[0] 'tls://dns.example:853': ConnectFailed (cause ConnectFailed)\n" ++
+            "FAIL upstreams[1] 'tls://other.example:853': ConnectFailed (cause ConnectFailed)\n",
         captured.out.written(),
     );
 }