feat(render): FR-010 verify output-prompt coverage + render->recover round-trip

Add Verify.checkOutputPrompt(fragment, requiredFieldNames) with the new
ERR_OUTPUT_PROMPT_FIELD_MISSING error code. Performs a substring scan of the
rendered output-format fragment to confirm every required field name appears in
the emitted skeleton — the build-time half of the prompt-fragment contract.

Add OutputPromptVerifyTest covering: coverage flags a missing field, coverage
passes when all fields present, JSON exampleOnly round-trip (render→recover)
produces no lostRequired, XML exampleOnly round-trip produces no lostRequired.
All four tests green; full render suite 211/211.

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

Author: dmealing

server/java/render/src/main/java/com/metaobjects/render/Verify.java

@@ -33,11 +33,38 @@ public final class Verify {
     public static final String ERR_REQUIRED_SLOT_UNUSED = "ERR_REQUIRED_SLOT_UNUSED";
     /** A declared {@code @requiredTags} output tag is absent from the template text. */
     public static final String ERR_OUTPUT_TAG_MISSING = "ERR_OUTPUT_TAG_MISSING";
+    /** A required field name is absent from the rendered output-format fragment. */
+    public static final String ERR_OUTPUT_PROMPT_FIELD_MISSING = "ERR_OUTPUT_PROMPT_FIELD_MISSING";
 
     static final int MAX_DEPTH = 32;
 
     private Verify() {}
 
+    // ---------------- Public API (output-prompt coverage) ----------------
+
+    /**
+     * Check that every required field name appears (as a substring) in the rendered
+     * output-format fragment. The check is a simple substring scan — field names are
+     * plain identifiers, so occurrence anywhere in the fragment is sufficient evidence
+     * that the renderer included the field.
+     *
+     * @param fragment        the rendered output-format fragment (XML or JSON skeleton)
+     * @param requiredFieldNames the field names that must appear in the fragment
+     * @return a list of {@link VerifyError} with code {@link #ERR_OUTPUT_PROMPT_FIELD_MISSING}
+     *         for every field name absent from the fragment; empty when all are present
+     */
+    public static List<VerifyError> checkOutputPrompt(String fragment, List<String> requiredFieldNames) {
+        List<VerifyError> errors = new ArrayList<>();
+        String haystack = fragment == null ? "" : fragment;
+        if (requiredFieldNames == null) return errors;
+        for (String name : requiredFieldNames) {
+            if (!haystack.contains(name)) {
+                errors.add(new VerifyError(ERR_OUTPUT_PROMPT_FIELD_MISSING, name));
+            }
+        }
+        return errors;
+    }
+
     // ---------------- Mustache tag token model (rendering-agnostic) ----------------
 
     sealed interface Tok permits VarTok, SectionTok, PartialTok {}

server/java/render/src/test/java/com/metaobjects/render/OutputPromptVerifyTest.java

@@ -0,0 +1,53 @@
+package com.metaobjects.render;
+
+import com.metaobjects.render.prompt.*;
+import com.metaobjects.render.recover.*;
+import org.junit.Test;
+import java.util.List;
+import java.util.Map;
+import static org.junit.Assert.*;
+
+public class OutputPromptVerifyTest {
+
+    @Test public void coverageFlagsMissingRequiredField() {
+        List<VerifyError> e = Verify.checkOutputPrompt("<Answer><text>hi</text></Answer>",
+                List.of("text", "confidence"));
+        assertEquals(1, e.size());
+        assertEquals(Verify.ERR_OUTPUT_PROMPT_FIELD_MISSING, e.get(0).code());
+        assertEquals("confidence", e.get(0).path());
+    }
+
+    @Test public void coverageAllPresentNoFindings() {
+        List<VerifyError> e = Verify.checkOutputPrompt("<Answer><text>hi</text><confidence>HIGH</confidence></Answer>",
+                List.of("text", "confidence"));
+        assertTrue(e.isEmpty());
+    }
+
+    @Test public void roundTripExampleOnlyRecoversComplete() {
+        // render the exampleOnly skeleton, then recover() it — required fields must all be present
+        OutputFormatSpec spec = new OutputFormatSpec(Format.JSON, "Answer", PromptStyle.EXAMPLE_ONLY, List.of(
+            new PromptField("text", FieldKind.STRING, true, false, null, null, "hi", null, null),
+            new PromptField("confidence", FieldKind.ENUM, true, false, List.of("HIGH"), null, "HIGH", null, null)));
+        String fragment = OutputFormatRenderer.render(spec, PromptOverrides.none());
+        String example = fragment.substring(fragment.indexOf('{'), fragment.lastIndexOf('}') + 1);
+
+        RecoverSchema rs = new RecoverSchema(Format.JSON, "Answer", List.of(
+            FieldSpec.scalar("text", FieldKind.STRING, true),
+            FieldSpec.enumField("confidence", true, List.of("HIGH"), Map.of())));
+        RecoverOutcome o = Recover.recover(example, rs, RecoverOptions.defaults());
+        assertTrue("round-trip complete (no lostRequired): " + o.report().lostRequired(),
+                o.report().lostRequired().isEmpty());
+    }
+
+    @Test public void roundTripXmlExampleOnly() {
+        OutputFormatSpec spec = new OutputFormatSpec(Format.XML, "Answer", PromptStyle.EXAMPLE_ONLY, List.of(
+            new PromptField("text", FieldKind.STRING, true, false, null, null, "hi", null, null),
+            new PromptField("confidence", FieldKind.ENUM, true, false, List.of("HIGH"), null, "HIGH", null, null)));
+        String fragment = OutputFormatRenderer.render(spec, PromptOverrides.none());
+        RecoverSchema rs = new RecoverSchema(Format.XML, "Answer", List.of(
+            FieldSpec.scalar("text", FieldKind.STRING, true),
+            FieldSpec.enumField("confidence", true, List.of("HIGH"), Map.of())));
+        RecoverOutcome o = Recover.recover(fragment, rs, RecoverOptions.defaults());
+        assertTrue("xml round-trip complete: " + o.report().lostRequired(), o.report().lostRequired().isEmpty());
+    }
+}