fix(render): FR-010 renderer — non-finite numerics stay valid JSON; close GUIDE+JSON + escaping test gaps

- C1: isNumericOrBoolean now rejects NaN/Infinity so those values are quoted (valid JSON) instead of emitted bare (invalid JSON)
- I1: remove assertFalse(out.contains("//")) from ExampleOnly + Inline tests — // inside a quoted string value is data, not a comment
- Add nanDoubleStaysValidJsonQuoted, urlValueDoesNotBreakJson, jsonValueWithQuotesStaysValid to ExampleOnlyTest
- Add guideJsonSkeletonIsValidJson to GuideTest (extracts skeleton after "Respond exactly like this:" to avoid prose braces)
- M1: precondition javadoc on OutputFormatSpec and PromptField noting rootName/name must be identifier-safe
- M2: inline comment in renderJsonSkeleton noting OBJECT/nested expansion is a Plan 3.1 deferral

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dmealing

server/java/render/src/main/java/com/metaobjects/render/prompt/OutputFormatRenderer.java

@@ -140,6 +140,8 @@ private static String renderJsonSkeleton(OutputFormatSpec spec, PromptOverrides
         List<PromptField> fields = spec.fields();
         for (int i = 0; i < fields.size(); i++) {
             PromptField field = fields.get(i);
+            // NOTE: FieldKind.OBJECT / nested fields are not expanded here — they render as a
+            // "{fieldName}" placeholder. Nested-object expansion is a Plan 3.1 deferral.
             String value = exampleValue(field, overrides);
             boolean isLast = i == fields.size() - 1;
             sb.append("  \"").append(field.name()).append("\": ");
@@ -178,10 +180,11 @@ private static boolean isNumericOrBoolean(FieldKind kind, String value) {
         if (!NUMERIC_KINDS.contains(kind)) return false;
         if (value.equals("true") || value.equals("false")) return true;
         try {
-            Double.parseDouble(value);
-            return true;
+            double d = Double.parseDouble(value);
+            return !Double.isNaN(d) && !Double.isInfinite(d);
         } catch (NumberFormatException e) {
-            return false;
+            // not a number; fall through to quoted string
         }
+        return false;
     }
 }

server/java/render/src/main/java/com/metaobjects/render/prompt/OutputFormatSpec.java

@@ -4,6 +4,10 @@
 import java.util.List;
 import java.util.Objects;
 
+/**
+ * Precondition: {@code rootName} must be identifier-safe (valid XML element name / JSON key).
+ * The renderer does not escape it.
+ */
 public record OutputFormatSpec(Format format, String rootName, PromptStyle style, List<PromptField> fields) {
     public OutputFormatSpec {
         Objects.requireNonNull(format, "format");

server/java/render/src/main/java/com/metaobjects/render/prompt/PromptField.java

@@ -4,7 +4,11 @@
 import java.util.List;
 import java.util.Map;
 
-/** enumValues/enumDoc non-null only for ENUM; nested non-null only for OBJECT; example/instruction nullable. */
+/**
+ * enumValues/enumDoc non-null only for ENUM; nested non-null only for OBJECT; example/instruction nullable.
+ * Precondition: {@code name} must be identifier-safe (valid XML element name / JSON key).
+ * The renderer does not escape field names.
+ */
 public record PromptField(String name, FieldKind kind, boolean required, boolean array,
                           List<String> enumValues, Map<String, String> enumDoc,
                           String example, String instruction, OutputFormatSpec nested) {}

server/java/render/src/test/java/com/metaobjects/render/prompt/OutputFormatRendererExampleOnlyTest.java

@@ -28,7 +28,6 @@ private OutputFormatSpec spec(Format fmt) {
 
     @Test public void jsonExampleBlockIsValidJson() throws Exception {
         String out = OutputFormatRenderer.render(spec(Format.JSON), PromptOverrides.none());
-        assertFalse("no // comments", out.contains("//"));
         int open = out.indexOf('{'), close = out.lastIndexOf('}');
         String json = out.substring(open, close + 1);
         var node = JSON.readTree(json);
@@ -41,4 +40,28 @@ private OutputFormatSpec spec(Format fmt) {
         String out = OutputFormatRenderer.render(spec(Format.XML), ov);
         assertTrue(out.contains("<text>OVERRIDDEN</text>"));
     }
+
+    @Test public void nanDoubleStaysValidJsonQuoted() throws Exception {
+        OutputFormatSpec s = new OutputFormatSpec(Format.JSON, "Answer", PromptStyle.EXAMPLE_ONLY, List.of(
+            new PromptField("score", FieldKind.DOUBLE, true, false, null, null, "NaN", null, null)));
+        String out = OutputFormatRenderer.render(s, PromptOverrides.none());
+        String json = out.substring(out.indexOf('{'), out.lastIndexOf('}') + 1);
+        assertEquals("NaN", JSON.readTree(json).get("score").asText());  // quoted string, valid JSON
+    }
+
+    @Test public void urlValueDoesNotBreakJson() throws Exception {
+        OutputFormatSpec s = new OutputFormatSpec(Format.JSON, "Answer", PromptStyle.EXAMPLE_ONLY, List.of(
+            new PromptField("link", FieldKind.STRING, true, false, null, null, "https://example.com/x", null, null)));
+        String out = OutputFormatRenderer.render(s, PromptOverrides.none());
+        String json = out.substring(out.indexOf('{'), out.lastIndexOf('}') + 1);
+        assertEquals("https://example.com/x", JSON.readTree(json).get("link").asText());
+    }
+
+    @Test public void jsonValueWithQuotesStaysValid() throws Exception {
+        OutputFormatSpec s = new OutputFormatSpec(Format.JSON, "Answer", PromptStyle.EXAMPLE_ONLY, List.of(
+            new PromptField("q", FieldKind.STRING, true, false, null, null, "she said \"hi\"", null, null)));
+        String out = OutputFormatRenderer.render(s, PromptOverrides.none());
+        String json = out.substring(out.indexOf('{'), out.lastIndexOf('}') + 1);
+        assertEquals("she said \"hi\"", JSON.readTree(json).get("q").asText());
+    }
 }

server/java/render/src/test/java/com/metaobjects/render/prompt/OutputFormatRendererGuideTest.java

@@ -36,4 +36,18 @@ private OutputFormatSpec spec() {
         PromptOverrides ov = new PromptOverrides(null, Map.of(), Map.of("text", "NEW INSTRUCTION"));
         assertTrue(OutputFormatRenderer.render(spec(), ov).contains("NEW INSTRUCTION"));
     }
+
+    @Test public void guideJsonSkeletonIsValidJson() throws Exception {
+        com.fasterxml.jackson.databind.ObjectMapper m = new com.fasterxml.jackson.databind.ObjectMapper();
+        OutputFormatSpec s = new OutputFormatSpec(Format.JSON, "Answer", PromptStyle.GUIDE, List.of(
+            new PromptField("text", FieldKind.STRING, true, false, null, null, "hi {now}", "say {x}", null),
+            new PromptField("confidence", FieldKind.ENUM, true, false, List.of("HIGH","LOW"),
+                Map.of("HIGH","Directly supported."), "HIGH", null, null)));
+        String out = OutputFormatRenderer.render(s, PromptOverrides.none());
+        String afterMarker = out.substring(out.indexOf("Respond exactly like this:"));
+        String json = afterMarker.substring(afterMarker.indexOf('{'), afterMarker.lastIndexOf('}') + 1);
+        var node = m.readTree(json);   // must parse even though prose above contains { } braces
+        assertEquals("hi {now}", node.get("text").asText());
+        assertEquals("HIGH", node.get("confidence").asText());
+    }
 }

server/java/render/src/test/java/com/metaobjects/render/prompt/OutputFormatRendererInlineTest.java

@@ -23,7 +23,6 @@ private OutputFormatSpec spec(Format f) {
     }
     @Test public void jsonInlineStillValid() throws Exception {
         String out = OutputFormatRenderer.render(spec(Format.JSON), PromptOverrides.none());
-        assertFalse(out.contains("//"));
         String json = out.substring(out.indexOf('{'), out.lastIndexOf('}') + 1);
         assertEquals("HIGH | OK | LOW", JSON.readTree(json).get("confidence").asText());
     }