fix: tolerate optional OKF index metadata

src/agent/index-middleware.ts

@@ -165,7 +165,7 @@ function renderLinks(
   return `# ${heading}\n\n${items.join("\n")}`;
 }
 
-/** Parses the optional title and description from YAML front matter. */
+/** Parses usable optional display metadata from YAML front matter. */
 function parseFrontmatter(
   content: string,
   filePath: string,
@@ -191,21 +191,20 @@ function parseFrontmatter(
   }
 
   const { description, title } = fields as Record<string, unknown>;
-  if (
-    description !== undefined &&
-    (typeof description !== "string" || !description.trim())
-  ) {
-    throw new Error(`${filePath} YAML description must be a non-empty string.`);
-  }
-  if (title !== undefined && typeof title !== "string") {
-    throw new Error(`${filePath} YAML title must be a string.`);
-  }
+  const usableDescription = usableString(description);
+  const usableTitle = usableString(title);
   return {
-    ...(description ? { description } : {}),
-    ...(title ? { title } : {}),
+    ...(usableDescription ? { description: usableDescription } : {}),
+    ...(usableTitle ? { title: usableTitle } : {}),
   };
 }
 
+/** Returns optional front matter text only when it can be rendered in an index. */
+function usableString(value: unknown): string | undefined {
+  if (typeof value !== "string" || !value.trim()) return undefined;
+  return value;
+}
+
 /** Converts an unknown thrown value into a readable message. */
 function errorMessage(error: unknown): string {
   return error instanceof Error ? error.message : String(error);

test/index-middleware.test.ts

@@ -151,20 +151,27 @@ describe("synchronizeWikiIndexes", () => {
     }
   });
 
-  test.each(["123", "[one, two]", "{ text: nested }"])(
-    "rejects a non-string YAML description: %s",
-    async (description) => {
-      const { backend } = await setup();
+  test.each([
+    ["123", "[one, two]"],
+    ["[one, two]", "{ text: nested }"],
+    ["{ text: nested }", ""],
+  ])(
+    "falls back when optional title and description are not usable strings: %s / %s",
+    async (title, description) => {
+      const { backend, rootDir } = await setup();
       await backend.write(
         "/openwiki/page.md",
-        `---\ntype: Reference\ndescription: ${description}\n---\n`,
+        `---\ntype: Reference\ntitle: ${title}\ndescription: ${description}\n---\n`,
       );
 
-      await expect(
-        synchronizeWikiIndexes(backend, "repository"),
-      ).rejects.toThrow(
-        "/openwiki/page.md YAML description must be a non-empty string.",
+      await synchronizeWikiIndexes(backend, "repository");
+
+      const index = await readFile(
+        path.join(rootDir, "openwiki/index.md"),
+        "utf8",
       );
+      expect(index).toContain("- [page](page.md)\n");
+      expect(index).not.toContain(" - ");
     },
   );