Reject missing prepared requests

integrations/ckprompt/preparation.go

@@ -100,6 +100,9 @@ func runRequestPreparation[I, S any](invocation commandkit.Invocation, suite Sui
 	if err := promptKitContextError(invocation.Context); err != nil {
 		return definitionFailure(fmt.Sprintf("Preparation of the PromptKit request for prompt %q was canceled.", input.promptID), acquired.Explanation, err)
 	}
+	if acquired.Value == nil {
+		return definitionFailure("PromptKit request preparation returned no result.", acquired.Explanation, nil)
+	}
 	_ = invocation.Reporter().Report(commandkit.Report{Value: acquired.Value})
 	return commandkit.Success()
 }

integrations/ckprompt/preparation_test.go

@@ -105,3 +105,43 @@ func TestNativePreparationBuilderAndErrorIdentity(t *testing.T) {
 		t.Fatalf("native error = %v", err)
 	}
 }
+
+func TestPreparationCommandRejectsMissingResultAndRetainsEvidence(t *testing.T) {
+	cause := errors.New("provider failure")
+	for _, tc := range []struct {
+		name        string
+		providerErr error
+		cancel      bool
+	}{
+		{name: "missing result"}, {name: "provider error", providerErr: cause}, {name: "cancellation", cancel: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			ctx, cancel := context.WithCancel(context.Background())
+			defer cancel()
+			app := newPromptTestApp(t, Command(Suite[struct{}, struct{}]{PrepareRequest: func(context.Context, PreparationRequest, struct{}, struct{}) (commandkit.Acquired[*promptkit.PreparedRun], error) {
+				if tc.cancel {
+					cancel()
+				}
+				acquired := commandkit.Acquired[*promptkit.PreparedRun]{
+					Diagnostics: []commandkit.Diagnostic{{Severity: commandkit.SeverityWarning, Write: func(w io.Writer) error { _, err := io.WriteString(w, "provider diagnostic\n"); return err }}},
+					Explanation: commandkit.Explanation{Message: "provider explanation"},
+				}
+				if tc.providerErr != nil {
+					acquired.Value = &promptkit.PreparedRun{PromptID: "briefing"}
+				}
+				return acquired, tc.providerErr
+			}}))
+			var output, diagnostics bytes.Buffer
+			result := app.Execute(ctx, []string{"promptkit", "show", "prepared", "briefing", "--format=json", "--verbose"}, commandkit.Streams{Out: &output, Err: &diagnostics})
+			if result.Kind != commandkit.OutcomeOperational || output.Len() != 0 || !bytes.Contains(diagnostics.Bytes(), []byte("provider diagnostic")) || !bytes.Contains(diagnostics.Bytes(), []byte("provider explanation")) {
+				t.Fatalf("result=%#v output=%q diagnostics=%q", result, output.String(), diagnostics.String())
+			}
+			if tc.providerErr != nil && !errors.Is(result.Cause, tc.providerErr) {
+				t.Fatalf("provider cause = %v", result.Cause)
+			}
+			if tc.cancel && !errors.Is(result.Cause, context.Canceled) {
+				t.Fatalf("cancellation cause = %v", result.Cause)
+			}
+		})
+	}
+}