Say that a readmodel and a reducer render to nothing

Source/Rendering.Cratis/Renderers/UnrenderedConstructs.cs

@@ -45,6 +45,17 @@ public static void Report(CSharpCodeBuilder builder, SliceSyntax slice, Rendered
             rendered.HasFlag(RenderedConstructs.ReadModel) ? slice.Projections.Count() - 1 : slice.Projections.Count(),
             "projection",
             "no read model is rendered for it.");
+
+        // A rendered read model is inferred from the slice's first projection, so at most one declared readmodel
+        // has a rendered counterpart — counted the same way the projections above are.
+        yield return (
+            rendered.HasFlag(RenderedConstructs.ReadModel) ? ReadModels(slice).Count() - 1 : ReadModels(slice).Count(),
+            "readmodel",
+            "nothing in the rendered application holds the state it declares.");
+        yield return (
+            Reducers(slice).Count(),
+            "reducer",
+            "the read model it builds is never populated in the rendered application.");
         yield return (
             rendered.HasFlag(RenderedConstructs.Reactors) ? 0 : slice.Reactors.Count(),
             "reactor",
@@ -74,4 +85,9 @@ public static void Report(CSharpCodeBuilder builder, SliceSyntax slice, Rendered
             "specification",
             "no specs are rendered for the generated application.");
     }
+
+    // Both collections are trailing optionals on SliceSyntax and are null on a slice that declares neither.
+    static IEnumerable<ReadModelSyntax> ReadModels(SliceSyntax slice) => slice.ReadModels ?? [];
+
+    static IEnumerable<ReducerSyntax> Reducers(SliceSyntax slice) => slice.Reducers ?? [];
 }

Source/Rendering.Cratis/for_UnrenderedConstructs/given/a_slice_declaring_every_family.cs

@@ -54,6 +54,10 @@ void Establish()
             [new ReactorTriggerSyntax("InvoiceRegistered", null, null, SourceLocation.Start)],
             SourceLocation.Start);
 
+        var readModel = new ReadModelSyntax("InvoiceSummary", [], SourceLocation.Start);
+
+        var reducer = new ReducerSyntax("InvoiceTotals", "InvoiceSummary", [], SourceLocation.Start);
+
         _slice = new SliceSyntax(
             SliceType.StateView,
             "Summary",
@@ -66,6 +70,8 @@ [new ReactorTriggerSyntax("InvoiceRegistered", null, null, SourceLocation.Start)
             [screen],
             [constraint],
             [specification],
-            SourceLocation.Start);
+            SourceLocation.Start,
+            ReadModels: [readModel],
+            Reducers: [reducer]);
     }
 }

Source/Rendering.Cratis/for_UnrenderedConstructs/when_reporting_what_a_slice_declares.cs

@@ -16,16 +16,24 @@ public class when_reporting_what_a_slice_declares : a_slice_declaring_every_fami
 
     void Because() => UnrenderedConstructs.Report(_builder, _slice, RenderedConstructs.None, _diagnostics);
 
-    [Fact] void should_report_every_family_it_declares() => _diagnostics.Count.ShouldEqual(9);
+    [Fact] void should_report_every_family_it_declares() => _diagnostics.Count.ShouldEqual(11);
     [Fact] void should_note_every_family_in_the_emitted_file() =>
-        _builder.ToString().Split('\n').Count(line => line.StartsWith("// TODO:", StringComparison.Ordinal)).ShouldEqual(9);
+        _builder.ToString().Split('\n').Count(line => line.StartsWith("// TODO:", StringComparison.Ordinal)).ShouldEqual(11);
     [Fact] void should_report_the_command() =>
         _diagnostics.ShouldContain(
             "Slice 'Summary' declares 1 command declaration(s) with no rendered equivalent — neither its input, the events it " +
             "produces nor its authorization is rendered.");
     [Fact] void should_report_the_projection() =>
         _diagnostics.ShouldContain(
             "Slice 'Summary' declares 1 projection declaration(s) with no rendered equivalent — no read model is rendered for it.");
+    [Fact] void should_report_the_read_model() =>
+        _diagnostics.ShouldContain(
+            "Slice 'Summary' declares 1 readmodel declaration(s) with no rendered equivalent — nothing in the rendered " +
+            "application holds the state it declares.");
+    [Fact] void should_report_the_reducer() =>
+        _diagnostics.ShouldContain(
+            "Slice 'Summary' declares 1 reducer declaration(s) with no rendered equivalent — the read model it builds is " +
+            "never populated in the rendered application.");
     [Fact] void should_report_the_reactor() =>
         _diagnostics.ShouldContain(
             "Slice 'Summary' declares 1 reactor declaration(s) with no rendered equivalent — nothing reacts to the events in the " +