refactor spec OKF

docs/rules/fragments/03_BundleStructure.md

@@ -0,0 +1,24 @@
+---
+type: Section
+title: Bundle Structure
+---
+
+# Bundle Structure
+
+A Knowledge Bundle is a self-contained, hierarchical collection of knowledge documents. The bundle root contains an `index.md` file that lists all concepts in the bundle. Each concept is a separate markdown file with its own frontmatter and body.
+
+## Directory Layout
+
+```
+bundle-root/
+├── index.md          # Bundle-level index (conventional filename)
+├── concept-a.md      # Top-level concept
+└── subdir/
+    └── concept-b.md  # Nested concept; ID = "subdir/concept-b"
+```
+
+Concept IDs are the file path without `.md`. A concept at `bundle-root/subdir/concept-b.md` has ID `subdir/concept-b`.
+
+## Index File
+
+The `index.md` at the bundle root is a conventional entry point listing all top-level concepts. It serves as progressive disclosure for large bundles.