Document DurableObjectRawFileSystem and snapshot helper

Update package docs to reflect a third concrete filesystem implementation: DurableObjectRawFileSystem — a thin DO KV-backed filesystem that commits every write synchronously for per-write durability. Add documentation for createFileSystemSnapshot which builds an InMemoryFileSystem from sync or async iterables of [path, content], enabling bridging async storage backends to the synchronous FileSystem interface. Also clarify an internal comment in file-system.ts to state the write-overlay is not re-exported from the package entry point.

Author: threepointone

.changeset/worker-bundler-filesystem.md

@@ -10,7 +10,7 @@ back the virtual filesystem with persistent or custom storage — for example, a
 `DurableObjectKVFileSystem` that buffers writes in memory and flushes to Durable
 Object KV on demand, avoiding a KV write for every individual file operation.
 
-Two concrete implementations are exported from the package:
+Three concrete implementations are exported from the package:
 
 - `InMemoryFileSystem` — a `Map`-backed filesystem suitable for tests and
   in-process pipelines. Accepts an optional seed object or `Map` of initial
@@ -19,6 +19,14 @@ Two concrete implementations are exported from the package:
   write-overlay. Writes accumulate in memory and are flushed to KV in one batch
   when `flush()` is called. Reads are served from the overlay first, so callers
   always observe their own writes immediately.
+- `DurableObjectRawFileSystem` — a thin Durable Object KV-backed filesystem
+  with no buffering. Every write is committed to KV synchronously. Use when
+  per-write durability is preferred over batching.
+
+`createFileSystemSnapshot` creates an `InMemoryFileSystem` from any sync or
+async iterable of `[path, content]` pairs, bridging async storage backends
+(e.g. `Workspace` from `@cloudflare/shell`) to the synchronous `FileSystem`
+interface.
 
 The `FileSystem.read()` method returns `string | null` (null = file does not
 exist) rather than an empty string, eliminating the need for a separate

packages/worker-bundler/src/file-system.ts

@@ -75,8 +75,9 @@ export class InMemoryFileSystem implements FileSystem {
 }
 
 /**
- * A generic write-overlay on top of any `FileSystem`. Not exported — intended
- * as an implementation detail for higher-level filesystem classes.
+ * A generic write-overlay on top of any `FileSystem`. Not re-exported from the
+ * package entry point — intended as an implementation detail for higher-level
+ * filesystem classes.
  *
  * Writes and deletes are buffered in memory keyed by the raw (untransformed)
  * path. Reads are served from the write buffer first; deleted paths return