docs(plugin): the planner door's hiddenIds contract is the answer, not the mechanism

src/plugin.ts

@@ -460,8 +460,10 @@ export interface MetadataIndexProvider {
    * @param params - The find params, already normalized by `find()`
    *   (natural-language parsed, `connected` anchors resolved to canonical ids,
    *   an empty `where` dropped).
-   * @param hiddenIds - Ids this read must not return; apply BEFORE paging so
-   *   `limit` stays exact.
+   * @param hiddenIds - Ids this read must not return. The contract is the ANSWER, not the
+   *   mechanism: a provider may subtract this set before paging, or derive the
+   *   same exclusion from the params' visibility tiers itself — either way the
+   *   page must equal the engine's own answer with none of these ids in it.
    * @param graphIndex - The active graph provider, for a `connected` plan.
    * @returns The page's ids plus the stage that emptied it, or `null`.
    */