feat: US-010 - Add fsync to VFS interface and implement write buffering in ChunkedVFS

Author: NathanFlurry

packages/core/src/kernel/kernel.ts

@@ -1527,6 +1527,9 @@ class KernelImpl implements Kernel {
 	private releaseDescriptionInode(
 		description: import("./types.js").FileDescription,
 	): void {
+		// Flush buffered writes to durable storage when the last FD is closed.
+		void this.vfs.fsync?.(description.path);
+
 		if (description.inode === undefined) return;
 		this.inodeTable.decrementOpenRefs(description.inode);
 		if (this.inodeTable.shouldDelete(description.inode)) {

packages/core/src/kernel/mount-table.ts

@@ -377,6 +377,11 @@ export class MountTable implements VirtualFileSystem {
 		return mount.fs.truncate(relativePath, length);
 	}
 
+	async fsync(path: string): Promise<void> {
+		const { mount, relativePath } = this.resolve(path);
+		await mount.fs.fsync?.(relativePath);
+	}
+
 	// -----------------------------------------------------------------------
 	// Helpers
 	// -----------------------------------------------------------------------

packages/core/src/kernel/vfs.ts

@@ -69,4 +69,7 @@ export interface VirtualFileSystem {
 
 	/** Write data at a specific offset without replacing the entire file. */
 	pwrite(path: string, offset: number, data: Uint8Array): Promise<void>;
+
+	/** Flush buffered writes for the given path to durable storage. */
+	fsync?(path: string): Promise<void>;
 }