diff --git a/.github/workflows/unit_tests.yml b/.github/workflows/unit_tests.yml
index aa173aa3..3a90ade9 100644
--- a/.github/workflows/unit_tests.yml
+++ b/.github/workflows/unit_tests.yml
@@ -124,7 +124,7 @@ jobs:
 
       - name: Test
         working-directory: ${{github.workspace}}/build
-        run: ctest -j $(nproc) -C ${{matrix.build_type}}
+        run: ctest --output-on-failure -j $(nproc) -C ${{matrix.build_type}}
 
   quality_checks_pass:
     runs-on: ${{ github.repository_owner == 'intel' && 'intel-' || '' }}ubuntu-22.04
@@ -218,7 +218,7 @@ jobs:
       - name: Test
         working-directory: ${{github.workspace}}/build
         run: |
-          ctest -j $(nproc) -E EXPECT_FAIL -T memcheck
+          ctest --output-on-failure -j $(nproc) -E "EXPECT_FAIL|PYTHON" -T memcheck
 
           LOGFILE=$(ls ./Testing/Temporary/LastDynamicAnalysis_*.log)
           FAILSIZE=$(du -c ./Testing/Temporary/MemoryChecker.* | tail -1 | cut -f1)
diff --git a/CMakeLists.txt b/CMakeLists.txt
index c619bed2..077ef6d9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,7 +23,7 @@ add_versioned_package(
     NAME
     fmt
     GIT_TAG
-    10.2.0
+    10.2.1
     GITHUB_REPOSITORY
     fmtlib/fmt
     OPTIONS
diff --git a/docs/flows.adoc b/docs/flows.adoc
index 3745dd80..0824580d 100644
--- a/docs/flows.adoc
+++ b/docs/flows.adoc
@@ -324,3 +324,59 @@ namespace example_component {
           SOME_ACTION && SOME_OTHER_ACTION));
 }
 ----
+
+=== Alternative flow builders
+
+The default flow service uses a graph builder that outputs the flow steps as an
+array of function pointers. Traversing the array and calling those functions
+ensures the correct relative ordering of flow steps in the graph, and this is
+what happens by default when we run the flow.
+
+[source,cpp]
+----
+// the default flow builder and service
+template <stdx::ct_string Name = "">
+using builder = flow::graph<Name, flow::graph_builder<impl>>;
+template <stdx::ct_string Name = "">
+struct service : cib::builder_meta<builder<Name>, flow::FunctionPtr> {};
+
+// declare a flow service
+struct MorningRoutine : public service<"MorningRoutine"> {};
+
+// add steps, etc, then at runtime, run the flow:
+nexus.service<"MorningRoutine">();
+----
+
+Here `graph_builder` is the type that renders the flow description into the
+array of function pointers, and `flow::FunctionPtr` is the type-erased interface
+(here a function taking and returning `void`) that is called to run a flow.
+
+But given a flow, other renderings are possible.
+
+[source,cpp]
+----
+// a flow builder and service that produces a graphviz rendering
+template <stdx::ct_string Name = "">
+using viz_builder = flow::graph<Name, flow::graphviz_builder>;
+template <stdx::ct_string Name = "">
+struct viz_service : cib::builder_meta<builder<Name>, flow::VizFunctionPtr> {};
+----
+
+Here, `viz_service` will produce a graphviz rendering of a flow using the
+`graphviz_builder`. `flow::VizFunctionPtr` is the type-erased interface once
+more, and it is defined to take `void` and return a `std::string`. When we "run"
+the flow, we get the graphviz rendering.
+
+[source,cpp]
+----
+// instead of the default flow::service, use the viz_service
+struct MorningRoutine : public viz_service<"MorningRoutine"> {};
+
+// add steps, etc, as before
+// this time, when we "run" the flow, we get a string representing the graphviz rendering
+auto graphviz_str = nexus.service<"MorningRoutine">();
+----
+
+`graphviz_builder` is available as a debugging aid. But in general, having the
+flow rendering separate from the flow definition enables any kind of rendering
+with correponding runtime behaviour.
diff --git a/include/flow/graphviz_builder.hpp b/include/flow/graphviz_builder.hpp
index 358e0b97..771c3c4c 100644
--- a/include/flow/graphviz_builder.hpp
+++ b/include/flow/graphviz_builder.hpp
@@ -7,6 +7,8 @@
 #include <string_view>
 
 namespace flow {
+using VizFunctionPtr = auto (*)() -> std::string;
+
 struct graphviz_builder {
     template <typename Graph>
     [[nodiscard]] static auto build(Graph const &input) {
@@ -49,5 +51,25 @@ struct graphviz_builder {
         output += "}";
         return output;
     }
+
+    template <typename Initialized> class built_flow {
+        static auto built() {
+            auto const v = Initialized::value;
+            return build(v);
+        }
+
+        static auto run() -> std::string { return built(); }
+
+      public:
+        // NOLINTNEXTLINE(google-explicit-constructor)
+        constexpr operator VizFunctionPtr() const { return run; }
+        auto operator()() const -> std::string { return run(); }
+        constexpr static bool active = true;
+    };
+
+    template <typename Initialized>
+    [[nodiscard]] constexpr static auto render() -> built_flow<Initialized> {
+        return {};
+    }
 };
 } // namespace flow
diff --git a/test/flow/flow.cpp b/test/flow/flow.cpp
index ea6b5370..a677f012 100644
--- a/test/flow/flow.cpp
+++ b/test/flow/flow.cpp
@@ -1,6 +1,7 @@
 #include <cib/cib.hpp>
 #include <cib/func_decl.hpp>
 #include <flow/flow.hpp>
+#include <flow/graphviz_builder.hpp>
 #include <log/fmt/logger.hpp>
 
 #include <catch2/catch_test_macros.hpp>
@@ -147,3 +148,28 @@ TEST_CASE("named flow logs milestones", "[flow]") {
     nexus.service<NamedTestFlow>();
     CHECK(log_buffer.find("flow.milestone(ms)") != std::string::npos);
 }
+
+namespace {
+template <stdx::ct_string Name = "">
+using alt_builder = flow::graph<Name, flow::graphviz_builder>;
+template <stdx::ct_string Name = "">
+struct alt_flow_service
+    : cib::builder_meta<alt_builder<Name>, flow::VizFunctionPtr> {};
+
+struct VizFlow : public alt_flow_service<"debug"> {};
+struct VizConfig {
+    constexpr static auto config =
+        cib::config(cib::exports<VizFlow>, cib::extend<VizFlow>(a));
+};
+} // namespace
+
+TEST_CASE("vizualize flow", "[flow]") {
+    cib::nexus<VizConfig> nexus{};
+    auto viz = nexus.service<VizFlow>();
+    auto expected = std::string{
+        R"__debug__(digraph debug {
+start -> a
+a -> end
+})__debug__"};
+    CHECK(viz == expected);
+}
diff --git a/test/flow/graph.cpp b/test/flow/graph.cpp
index f76613f9..ebcff152 100644
--- a/test/flow/graph.cpp
+++ b/test/flow/graph.cpp
@@ -20,32 +20,32 @@ constexpr auto b = flow::action<"b">([] {});
 constexpr auto c = flow::action<"c">([] {});
 } // namespace
 
-TEST_CASE("node size (empty graph)", "[flow]") {
+TEST_CASE("node size (empty graph)", "[graph]") {
     constexpr auto g = flow::graph<>{};
     static_assert(node_size(g) == 0);
 }
 
-TEST_CASE("node size (single action)", "[flow]") {
+TEST_CASE("node size (single action)", "[graph]") {
     constexpr auto g = flow::graph<>{}.add(a >> b);
     static_assert(node_size(g) == 2);
 }
 
-TEST_CASE("node size (overlapping actions)", "[flow]") {
+TEST_CASE("node size (overlapping actions)", "[graph]") {
     constexpr auto g = flow::graph<>{}.add(a >> b).add(b >> c);
     static_assert(node_size(g) == 3);
 }
 
-TEST_CASE("edge size (empty flow)", "[flow]") {
+TEST_CASE("edge size (empty flow)", "[graph]") {
     constexpr auto g = flow::graph<>{};
     static_assert(edge_size(g) == 1);
 }
 
-TEST_CASE("edge size (single action)", "[flow]") {
+TEST_CASE("edge size (single action)", "[graph]") {
     constexpr auto g = flow::graph<>{}.add(a >> b);
     static_assert(edge_size(g) == 1);
 }
 
-TEST_CASE("edge size (overlapping actions)", "[flow]") {
+TEST_CASE("edge size (overlapping actions)", "[graph]") {
     constexpr auto g = flow::graph<>{}.add(a >> b).add(b >> c);
     static_assert(edge_size(g) == 2);
 }
diff --git a/test/flow/graph_builder.cpp b/test/flow/graph_builder.cpp
index 140047e4..a3131abe 100644
--- a/test/flow/graph_builder.cpp
+++ b/test/flow/graph_builder.cpp
@@ -19,14 +19,14 @@ constexpr auto d = flow::action<"d">([] { actual += "d"; });
 using builder = flow::graph_builder<flow::impl>;
 } // namespace
 
-TEST_CASE("build and run empty flow", "[flow]") {
+TEST_CASE("build and run empty flow", "[graph_builder]") {
     auto g = flow::graph<>{};
     auto const flow = builder::build(g);
     REQUIRE(flow.has_value());
     flow.value()();
 }
 
-TEST_CASE("add single action", "[flow]") {
+TEST_CASE("add single action", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a);
     auto const flow = builder::build(g);
@@ -35,7 +35,7 @@ TEST_CASE("add single action", "[flow]") {
     CHECK(actual == "a");
 }
 
-TEST_CASE("two milestone linear before dependency", "[flow]") {
+TEST_CASE("two milestone linear before dependency", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a >> milestone0);
     auto const flow = builder::build(g);
@@ -44,7 +44,7 @@ TEST_CASE("two milestone linear before dependency", "[flow]") {
     CHECK(actual == "a");
 }
 
-TEST_CASE("actions get executed once", "[flow]") {
+TEST_CASE("actions get executed once", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}
                  .add(a >> milestone0)
@@ -55,7 +55,7 @@ TEST_CASE("actions get executed once", "[flow]") {
     CHECK(actual == "a");
 }
 
-TEST_CASE("two milestone linear after dependency", "[flow]") {
+TEST_CASE("two milestone linear after dependency", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}
                  .add(a >> milestone0)
@@ -66,7 +66,8 @@ TEST_CASE("two milestone linear after dependency", "[flow]") {
     CHECK(actual == "ab");
 }
 
-TEST_CASE("three milestone linear before and after dependency", "[flow]") {
+TEST_CASE("three milestone linear before and after dependency",
+          "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a >> b >> c);
     auto const flow = builder::build(g);
@@ -74,7 +75,7 @@ TEST_CASE("three milestone linear before and after dependency", "[flow]") {
     CHECK(actual == "abc");
 }
 
-TEST_CASE("just two actions in order", "[flow]") {
+TEST_CASE("just two actions in order", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a >> b);
     auto const flow = builder::build(g);
@@ -82,7 +83,7 @@ TEST_CASE("just two actions in order", "[flow]") {
     CHECK(actual == "ab");
 }
 
-TEST_CASE("insert action between two actions", "[flow]") {
+TEST_CASE("insert action between two actions", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a >> c).add(a >> b >> c);
     auto const flow = builder::build(g);
@@ -90,7 +91,7 @@ TEST_CASE("insert action between two actions", "[flow]") {
     CHECK(actual == "abc");
 }
 
-TEST_CASE("add single parallel 2", "[flow]") {
+TEST_CASE("add single parallel 2", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a && b);
     auto const flow = builder::build(g);
@@ -101,7 +102,7 @@ TEST_CASE("add single parallel 2", "[flow]") {
     CHECK(actual.size() == 2);
 }
 
-TEST_CASE("add single parallel 3", "[flow]") {
+TEST_CASE("add single parallel 3", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a && b && c);
     auto const flow = builder::build(g);
@@ -113,7 +114,7 @@ TEST_CASE("add single parallel 3", "[flow]") {
     CHECK(actual.size() == 3);
 }
 
-TEST_CASE("add single parallel 3 with later dependency 1", "[flow]") {
+TEST_CASE("add single parallel 3 with later dependency 1", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a && b && c).add(c >> a);
     auto const flow = builder::build(g);
@@ -126,7 +127,7 @@ TEST_CASE("add single parallel 3 with later dependency 1", "[flow]") {
     CHECK(actual.size() == 3);
 }
 
-TEST_CASE("add single parallel 3 with later dependency 2", "[flow]") {
+TEST_CASE("add single parallel 3 with later dependency 2", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a && b && c).add(a >> c);
     auto const flow = builder::build(g);
@@ -139,7 +140,7 @@ TEST_CASE("add single parallel 3 with later dependency 2", "[flow]") {
     CHECK(actual.size() == 3);
 }
 
-TEST_CASE("add parallel rhs", "[flow]") {
+TEST_CASE("add parallel rhs", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a >> (b && c));
     auto const flow = builder::build(g);
@@ -153,7 +154,7 @@ TEST_CASE("add parallel rhs", "[flow]") {
     CHECK(actual.size() == 3);
 }
 
-TEST_CASE("add parallel lhs", "[flow]") {
+TEST_CASE("add parallel lhs", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add((a && b) >> c);
     auto const flow = builder::build(g);
@@ -167,7 +168,7 @@ TEST_CASE("add parallel lhs", "[flow]") {
     CHECK(actual.size() == 3);
 }
 
-TEST_CASE("add parallel in the middle", "[flow]") {
+TEST_CASE("add parallel in the middle", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a >> (b && c) >> d);
     auto const flow = builder::build(g);
@@ -187,7 +188,7 @@ TEST_CASE("add parallel in the middle", "[flow]") {
     CHECK(actual.size() == 4);
 }
 
-TEST_CASE("add dependency lhs", "[flow]") {
+TEST_CASE("add dependency lhs", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add((a >> b) && c);
     auto const flow = builder::build(g);
@@ -202,7 +203,7 @@ TEST_CASE("add dependency lhs", "[flow]") {
     CHECK(actual.size() == 3);
 }
 
-TEST_CASE("add dependency rhs", "[flow]") {
+TEST_CASE("add dependency rhs", "[graph_builder]") {
     actual.clear();
     auto g = flow::graph<>{}.add(a && (b >> c));
     auto const flow = builder::build(g);
@@ -217,7 +218,7 @@ TEST_CASE("add dependency rhs", "[flow]") {
     CHECK(actual.size() == 3);
 }
 
-TEST_CASE("alternate builder", "[flow]") {
+TEST_CASE("alternate builder", "[graph_builder]") {
     using alt_builder = flow::graphviz_builder;
     auto g = flow::graph<"debug">{}.add(a && (b >> c));
     auto const flow = alt_builder::build(g);