fix(judge): parse balanced JSON responses

apps/judge/src/judge-strategies.test.ts

@@ -470,6 +470,9 @@ class TestableBundledStrategy extends BundledStrategy {
   publicBuildSystemPrompt(hasToolOutputs: boolean, hasAgentResponse?: boolean) {
     return (this as any).buildSystemPrompt(undefined, hasToolOutputs, hasAgentResponse);
   }
+  publicParseJsonResponse(response: string, criteria: { id: string; prompt: string }[]) {
+    return (this as any).parseJsonResponse(response, criteria);
+  }
   publicBuildUserPrompt(
     criteria: { id: string; prompt: string }[] = [
       { id: "c1", prompt: "does the code work" },
@@ -480,6 +483,31 @@ class TestableBundledStrategy extends BundledStrategy {
   }
 }
 
+describe("BundledStrategy JSON parsing (issue #167)", () => {
+  const criteria = [{ id: "c1", prompt: "criterion one" }];
+
+  it("parses fenced JSON with nested objects", () => {
+    const response = '```json\n{"results":[{"criterion":"c1","passed":true,"feedback":"details"}],"meta":{"tokens":1}}\n```';
+    const result = new TestableBundledStrategy("test-model").publicParseJsonResponse(response, criteria);
+    expect(result.allPassed).toBe(true);
+    expect(result.results[0].evaluated).toBe(true);
+  });
+
+  it("ignores braces inside JSON strings", () => {
+    const response = '{"results":[{"criterion":"c1","passed":true,"feedback":"mongoose } config { is present"}]} trailing text';
+    const result = new TestableBundledStrategy("test-model").publicParseJsonResponse(response, criteria);
+    expect(result.allPassed).toBe(true);
+    expect(result.results[0].feedback).toContain("mongoose } config {");
+  });
+
+  it("treats truncated JSON as unevaluated", () => {
+    const response = '```json\n{"results":[{"criterion":"c1","passed":false,"feedback":"truncated';
+    const result = new TestableBundledStrategy("test-model").publicParseJsonResponse(response, criteria);
+    expect(result.allPassed).toBe(false);
+    expect(result.results[0].evaluated).toBe(false);
+  });
+});
+
 describe("judge tool-outputs guidance (issue #1125)", () => {
   // The headless judge cannot run commands; it must decide from the codebase
   // plus the coding agent's captured tool outputs. The guidance must be generic

apps/judge/src/judge-strategies.ts

@@ -1002,23 +1002,39 @@ IMPORTANT: Return ONLY the JSON, no additional text before or after.`;
 ${criteriaList}${historySection}`;
   }
 
+  /** Extract the first complete JSON object, respecting strings and escapes. */
+  private extractJsonObject(response: string): string | undefined {
+    const start = response.indexOf("{");
+    if (start < 0) return undefined;
+
+    let depth = 0;
+    let inString = false;
+    let escaped = false;
+    for (let i = start; i < response.length; i++) {
+      const ch = response[i];
+      if (inString) {
+        if (escaped) escaped = false;
+        else if (ch === "\\") escaped = true;
+        else if (ch === '"') inString = false;
+        continue;
+      }
+      if (ch === '"') inString = true;
+      else if (ch === "{") depth++;
+      else if (ch === "}" && --depth === 0) return response.slice(start, i + 1);
+    }
+    return undefined;
+  }
+
   private parseJsonResponse(
     response: string,
     criteria: CriteriaConfig[],
     onProgress?: (result: CriterionResult) => void,
   ): DetailedEvaluationResult {
-    // Try to extract JSON from markdown code blocks
-    let jsonStr = response.trim();
-    const jsonMatch = jsonStr.match(/```(?:json)?\s*(\{[\s\S]*?\})\s*```/);
-    if (jsonMatch) {
-      jsonStr = jsonMatch[1];
-    } else {
-      // Try to find raw JSON
-      const rawJsonMatch = jsonStr.match(/(\{[\s\S]*\})/);
-      if (rawJsonMatch) {
-        jsonStr = rawJsonMatch[1];
-      }
-    }
+    // Extract a complete JSON object without relying on markdown fences. A
+    // brace-balanced scan handles nested objects and braces inside feedback strings,
+    // while an incomplete/truncated response deliberately falls through to the
+    // existing parse-error path.
+    const jsonStr = this.extractJsonObject(response) ?? response.trim();
 
     try {
       const data = JSON.parse(jsonStr);