fix(sdk): make engine-layer PR self-contained — trim index.ts, guard indexed access

- index.ts no longer exports document/session/history/persist-queue (those
  modules land in the next stacked PR); branch now typechecks standalone
- setOwnText: optional-chain children[i] access (TS2532 under
  noUncheckedIndexedAccess)
- fallow suppressions for buildPatchEvent + adapters/types.ts — consumers
  arrive in #1325

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: vanceingalls

packages/sdk/src/adapters/types.ts

@@ -1,3 +1,5 @@
+// Consumed by session.ts + adapter implementations in the next stacked PR (#1325).
+// fallow-ignore-file unused-file
 import type { PersistErrorEvent } from "../types.js";
 
 // ─── PersistAdapter ───────────────────────────────────────────────────────────

packages/sdk/src/engine/model.ts

@@ -116,7 +116,7 @@ export function setOwnText(el: Element, text: string): void {
   // Track original position of the first text node so we restore there, not at firstChild.
   let firstTextIdx = -1;
   for (let i = 0; i < children.length; i++) {
-    if (children[i].nodeType === 3) {
+    if (children[i]?.nodeType === 3) {
       firstTextIdx = i;
       break;
     }

packages/sdk/src/engine/patches.ts

@@ -105,6 +105,8 @@ export function pathToKey(path: string): string | null {
 
 // ─── Patch event builder ──────────────────────────────────────────────────────
 
+// Consumed by session.ts dispatch/batch in the next stacked PR (#1325).
+// fallow-ignore-next-line unused-export
 export function buildPatchEvent(
   forward: readonly JsonPatchOp[],
   inverse: readonly JsonPatchOp[],

packages/sdk/src/index.ts

@@ -17,14 +17,3 @@ export type {
 } from "./types.js";
 
 export { ORIGIN_APPLY_PATCHES, ORIGIN_LOCAL } from "./types.js";
-
-export { buildDocument, flatElements } from "./document.js";
-
-export { openComposition } from "./session.js";
-export type { OpenCompositionOptions } from "./session.js";
-
-export { createHistory } from "./history.js";
-export type { HistoryModule, HistoryOptions, HistoryEntry } from "./history.js";
-
-export { createPersistQueue } from "./persist-queue.js";
-export type { PersistQueueModule, PersistQueueOptions } from "./persist-queue.js";