fix: user metadata named 'level' is a real field everywhere — the engine-internal node layer no longer shadows it in sort/filter/aggregation, and the indexing views stop stamping a phantom 0 into its column; index epoch 2 rebuilds existing brains at first open

Also completes the v8.10.2 write-granularity law for the transact() plan
path: a metadata-only batch update never rewrites the vector-bearing noun
record (planUpdate staged the unconditional save the update() fix removed).
Seven pins in tests/integration/level-field-shadow.test.ts including the
reporting consumer's exact repro rows; orderBy JSDoc documents the ordering
contract and the announced field-addressing law.

src/types/brainy.types.ts

@@ -551,7 +551,23 @@ export interface FindParams<T = any> {
   cursor?: string            // Cursor-based pagination
 
   // Sorting
-  orderBy?: string           // Field to sort by (e.g., 'createdAt', 'title', 'metadata.priority')
+  /**
+   * Field to sort by. User metadata fields sort by their stored values —
+   * including natural names like `level`, `rank`, or `score` (an engine-internal
+   * field can never shadow your metadata; fixed 2026-08 after a production
+   * report). System timestamps (`createdAt`, `updatedAt`) sort by entity age.
+   *
+   * Ordering contract (identical on the pure-JS engine and the native
+   * accelerator): entities missing the field sort LAST in both directions —
+   * they are never dropped from the result; ties break deterministically.
+   *
+   * NOTE — the field-addressing law is changing (announced 2026-08): bare
+   * names will mean user metadata ALWAYS, and system fields will be reached
+   * explicitly as `system.<field>` (e.g. `system.createdAt`), with typed
+   * refusals for unresolvable names. Until that release, bare `createdAt`
+   * and friends keep resolving to the system fields as documented above.
+   */
+  orderBy?: string
   order?: 'asc' | 'desc'     // Sort direction: 'asc' (default) or 'desc'
 
   // Advanced options