diff --git a/docs/plugins/sdk-subpaths.md b/docs/plugins/sdk-subpaths.md
index 6b8e1ae9aeed..1601352d6bdd 100644
--- a/docs/plugins/sdk-subpaths.md
+++ b/docs/plugins/sdk-subpaths.md
@@ -416,7 +416,7 @@ Use `isLoopbackHost(host)` when a plugin must accept only the local machine. It
     | `plugin-sdk/concurrency-runtime` | Private-local after July 2026; Bounded async task concurrency (`runTasksWithConcurrency`) and cancellable permit admission (`createPermitPool`) with caller-owned release |
     | `plugin-sdk/dedupe-runtime` | In-memory and persistent-backed dedupe cache helpers |
     | `plugin-sdk/delivery-queue-runtime` | Private-local after July 2026; Outbound pending-delivery drain helper |
-    | `plugin-sdk/file-access-runtime` | Private-local after July 2026; Safe local-file, path-containment, temp-root, media-source path, directory-durability, and borrowed-handle readers: `readFileHandleBounded` reads through EOF under a byte cap; `readFileWindowFully` fills a positional buffer through short reads; `sha256File` streams a bounded SHA-256 digest from a path or borrowed handle. Borrowed handles stay open. `resolvePathPrefixSync` observes a canonical existing prefix and raw missing suffix, following physical symlink traversal without authorizing later access. |
+    | `plugin-sdk/file-access-runtime` | Private-local after July 2026; Safe local-file, path-containment, temp-root, media-source path, directory-durability, and borrowed-handle I/O: `readFileHandleBounded` reads through EOF under a byte cap; `readFileWindowFully` fills a positional buffer through short reads; `writeFileWindowFully` completes short writes without truncation, synchronization, or rollback; `sha256File` streams a bounded SHA-256 digest from a path or borrowed handle. Borrowed handles stay open. `resolvePathPrefixSync` observes a canonical existing prefix and raw missing suffix, following physical symlink traversal without authorizing later access. |
     | `plugin-sdk/heartbeat-runtime` | Private-local after July 2026; Heartbeat wake, event, and visibility helpers |
     | `plugin-sdk/expect-runtime` | Private-local after July 2026; Required-value assertion helper for provable runtime invariants |
     | `plugin-sdk/number-runtime` | Private-local after July 2026; Numeric coercion helper |
diff --git a/extensions/memory-core/src/short-term-promotion-memory-write.ts b/extensions/memory-core/src/short-term-promotion-memory-write.ts
index e966a4310767..ef012d02afaa 100644
--- a/extensions/memory-core/src/short-term-promotion-memory-write.ts
+++ b/extensions/memory-core/src/short-term-promotion-memory-write.ts
@@ -2,7 +2,10 @@ import { createHash } from "node:crypto";
 import fs from "node:fs/promises";
 import path from "node:path";
 import { extractErrorCode } from "openclaw/plugin-sdk/error-runtime";
-import { resolvePathPrefixSync } from "openclaw/plugin-sdk/file-access-runtime";
+import {
+  resolvePathPrefixSync,
+  writeFileWindowFully,
+} from "openclaw/plugin-sdk/file-access-runtime";
 import type { MemoryWorkspaceFiles } from "openclaw/plugin-sdk/memory-core-host-engine-storage";
 import { replaceFileAtomic } from "openclaw/plugin-sdk/security-runtime";
 import { getMemoryWorkspaceMaintenance, readWorkspaceText } from "./memory-workspace-files.js";
@@ -114,21 +117,7 @@ async function writeExistingMemoryInPlace(params: {
   } catch (error) {
     const original = Buffer.from(params.expectedContent, "utf-8");
     try {
-      let restored = 0;
-      while (restored < original.length) {
-        const { bytesWritten } = await handle.write(
-          original,
-          restored,
-          original.length - restored,
-          restored,
-        );
-        if (bytesWritten <= 0) {
-          throw new Error(`${path.basename(params.filePath)} restore write made no progress`, {
-            cause: error,
-          });
-        }
-        restored += bytesWritten;
-      }
+      await writeFileWindowFully(handle, original, 0);
       await handle.truncate(original.length);
       await handle.sync();
     } catch (restoreError) {
diff --git a/src/plugin-sdk/file-access-runtime.ts b/src/plugin-sdk/file-access-runtime.ts
index 2d038d8a18b3..5f296640c4c2 100644
--- a/src/plugin-sdk/file-access-runtime.ts
+++ b/src/plugin-sdk/file-access-runtime.ts
@@ -28,6 +28,7 @@ export {
   resolvePathPrefixSync,
 } from "../infra/fs-safe-advanced.js";
 export { readFileWindowFully } from "../infra/file-read.js";
+export { writeFileWindowFully } from "../infra/file-descriptor.js";
 export { openRootFile } from "../infra/boundary-file-read.js";
 export {
   ensureDurableDirectory,