fix(sdk): export adapter types, awaitable flush(), never-coalesce mode

- Export PersistAdapter, PreviewAdapter, PersistVersionEntry from package
  root — callers can now write typed fakes without reaching into internals
- Add flush(): Promise<void> to Composition interface + CompositionImpl —
  app-close handlers can await a clean drain of the persist queue
- coalesceMs <= 0 disables coalescing entirely in createHistory — enables
  deterministic test scenarios without per-entry timestamp manipulation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: vanceingalls

packages/sdk/src/history.ts

@@ -68,6 +68,7 @@ export function createHistory(session: Composition, opts: HistoryOptions = {}):
   }
 
   function shouldCoalesce(entry: HistoryEntry, incoming: PatchEvent): boolean {
+    if (coalesceMs <= 0) return false;
     if (opTypesKey(entry.opTypes) !== opTypesKey(incoming.opTypes)) return false;
     if (entry.origin !== incoming.origin) return false;
     // Coalesce only when the SAME paths are touched (e.g. slider drag on one

packages/sdk/src/index.ts

@@ -30,3 +30,5 @@ export type { HistoryModule, HistoryOptions, HistoryEntry } from "./history.js";
 
 export { createPersistQueue } from "./persist-queue.js";
 export type { PersistQueueModule, PersistQueueOptions } from "./persist-queue.js";
+
+export type { PersistAdapter, PreviewAdapter, PersistVersionEntry } from "./adapters/types.js";

packages/sdk/src/session.ts

@@ -391,6 +391,10 @@ class CompositionImpl implements Composition {
 
   // ── Lifecycle ────────────────────────────────────────────────────────────────
 
+  async flush(): Promise<void> {
+    await this.persistQueueModule?.flush();
+  }
+
   dispose(): void {
     this.persistQueueModule?.dispose();
     this.historyModule?.dispose();

packages/sdk/src/types.ts

@@ -252,5 +252,7 @@ export interface Composition {
   applyPatches(patches: readonly JsonPatchOp[], opts?: { origin?: unknown }): void;
 
   // ── Lifecycle ──────────────────────────────────────────────────────────────
+  /** Drain the persist queue — resolves when any queued write is committed. No-op if no adapter. */
+  flush(): Promise<void>;
   dispose(): void;
 }