fix: append deterministic meta block to parent_canon.md

LLM was hallucinating timestamps in the meta section. Now
appends a code-generated meta block with real parentBookId,
parentTitle, and generatedAt after LLM output.

packages/core/src/pipeline/runner.ts

@@ -745,8 +745,19 @@ ${matrix}`,
       },
     ], { temperature: 0.3, maxTokens: 16384 });
 
-    await writeFile(join(storyDir, "parent_canon.md"), response.content, "utf-8");
-    return response.content;
+    // Append deterministic meta block (LLM may hallucinate timestamps)
+    const metaBlock = [
+      "",
+      "---",
+      "meta:",
+      `  parentBookId: "${parentBookId}"`,
+      `  parentTitle: "${parentBook.title}"`,
+      `  generatedAt: "${new Date().toISOString()}"`,
+    ].join("\n");
+    const canon = response.content + metaBlock;
+
+    await writeFile(join(storyDir, "parent_canon.md"), canon, "utf-8");
+    return canon;
   }
 
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