Harden render validation tests for input paths and empty transcript output

internal/cli/render_test.go

@@ -224,6 +224,40 @@ func TestRenderSupportsMinimalIntermediateAndFullInputs(t *testing.T) {
 	}
 }
 
+func TestRenderEmptyTranscriptIsDeterministic(t *testing.T) {
+	dir := t.TempDir()
+	input := writeJSONFile(t, dir, "input.json", `{
+		"metadata": {
+			"application": "seriatim",
+			"version": "v-test",
+			"output_schema": "seriatim-minimal"
+		},
+		"segments": []
+	}`)
+	output := writeJSONFile(t, dir, "output.md", "")
+
+	run := func() string {
+		err := executeRender(
+			"--input-file", input,
+			"--output-file", output,
+			"--format", config.RenderFormatMarkdown,
+		)
+		if err != nil {
+			t.Fatalf("render failed: %v", err)
+		}
+		return readFile(t, output)
+	}
+
+	first := run()
+	second := run()
+	if first != second {
+		t.Fatalf("empty transcript render is not deterministic:\nfirst:\n%s\nsecond:\n%s", first, second)
+	}
+	if first != "# Transcript\n" {
+		t.Fatalf("unexpected empty transcript output:\n%s", first)
+	}
+}
+
 func executeRender(args ...string) error {
 	cmd := NewRootCommand()
 	cmd.SetArgs(append([]string{"render"}, args...))