diff --git a/packages/op-vscode/src/vscode/pen-editor-provider.ts b/packages/op-vscode/src/vscode/pen-editor-provider.ts
index 6b7c65583..1ce8c3edd 100644
--- a/packages/op-vscode/src/vscode/pen-editor-provider.ts
+++ b/packages/op-vscode/src/vscode/pen-editor-provider.ts
@@ -15,6 +15,7 @@ import type { BridgeOutboundToPage } from "../protocol/bridge";
 import { encodeOutbound } from "../protocol/bridge";
 import { buildBootHtml, buildWebviewHtml } from "./webview-shell";
 import { pickRestartSource, resolveDaemonBinary, type LatestDurable } from "./restart-source";
+import { isShellControl, parseShellReadyOrigin } from "./shell-messages";
 
 const SHELL_READY_TIMEOUT_MS = 5_000;
 const DAEMON_READY_TIMEOUT_MS = 10_000;
@@ -263,6 +264,7 @@ export class PenEditorProvider implements vscode.CustomEditorProvider<PenDocumen
       },
       writeBackup: async (name, bytes) => {
         const uri = this.backupUri(name);
+        await ensureParentDir(uri);
         await vscode.workspace.fs.writeFile(uri, bytes);
       },
       writeBackupFallback: async (bytes) => {
@@ -337,6 +339,7 @@ export class PenEditorProvider implements vscode.CustomEditorProvider<PenDocumen
     cancellation: vscode.CancellationToken,
   ): Promise<vscode.CustomDocumentBackup> {
     const bytes = await this.requireSession(document).backup(() => cancellation.isCancellationRequested);
+    await ensureParentDir(context.destination); // VS Code: the backup dir may not exist
     await vscode.workspace.fs.writeFile(context.destination, bytes);
     document.latestDurable = { source: "backup", json: decode(bytes) };
     return {
@@ -376,6 +379,13 @@ function decode(bytes: Uint8Array): string {
   return decoder.decode(bytes);
 }
 
+/** Ensure a URI's parent directory exists (createDirectory is recursive and a
+ *  no-op if present). VS Code does not guarantee storage / backup-destination
+ *  dirs exist on a fresh profile. */
+async function ensureParentDir(uri: vscode.Uri): Promise<void> {
+  await vscode.workspace.fs.createDirectory(vscode.Uri.joinPath(uri, ".."));
+}
+
 /** Atomic write: temp file + rename, so a crash mid-write can't truncate. */
 async function atomicWrite(uri: vscode.Uri, bytes: Uint8Array): Promise<void> {
   const tmp = uri.with({ path: `${uri.path}.op-tmp` });
@@ -393,22 +403,6 @@ function delay(ms: number): Promise<void> {
   return new Promise((r) => setTimeout(r, ms));
 }
 
-/** Parse an op-shell/ready control message → its reported origin, else undefined. */
-function parseShellReadyOrigin(raw: unknown): string | undefined {
-  if (typeof raw !== "string") return undefined;
-  try {
-    const v = JSON.parse(raw) as { type?: unknown; origin?: unknown };
-    if (v.type === "op-shell/ready" && typeof v.origin === "string") return v.origin;
-  } catch {
-    /* not a control message */
-  }
-  return undefined;
-}
-
-function isShellControl(raw: unknown): boolean {
-  return typeof raw === "string" && raw.includes("op-shell/");
-}
-
 function errorPage(detail: string): string {
   const safe = detail.replace(/[<&]/g, (c) => (c === "<" ? "&lt;" : "&amp;"));
   return `<!doctype html><html><body style="font-family:sans-serif;padding:2rem;color:var(--vscode-foreground)">
diff --git a/packages/op-vscode/src/vscode/shell-messages.test.ts b/packages/op-vscode/src/vscode/shell-messages.test.ts
new file mode 100644
index 000000000..64b841deb
--- /dev/null
+++ b/packages/op-vscode/src/vscode/shell-messages.test.ts
@@ -0,0 +1,38 @@
+import { test, expect } from "bun:test";
+import { isShellControl, parseShellReadyOrigin } from "./shell-messages";
+
+test("isShellControl matches only a top-level op-shell/ type", () => {
+  expect(isShellControl(JSON.stringify({ type: "op-shell/ready", origin: "x" }))).toBe(true);
+  expect(isShellControl(JSON.stringify({ type: "op-bridge/snapshot-result", requestId: "r" }))).toBe(false);
+});
+
+test("isShellControl does NOT drop a snapshot whose docJson embeds op-shell/", () => {
+  // Regression: a legitimate snapshot-result carrying "op-shell/" inside its
+  // docJson must reach the session — a substring check would drop it and hang
+  // the awaiting save/backup.
+  const msg = JSON.stringify({
+    type: "op-bridge/snapshot-result",
+    requestId: "r1",
+    docJson: '{"text":"see op-shell/ready docs"}',
+    generation: 2,
+    revision: 1,
+  });
+  expect(msg).toContain("op-shell/");
+  expect(isShellControl(msg)).toBe(false);
+});
+
+test("isShellControl rejects non-string / non-JSON / typeless payloads", () => {
+  expect(isShellControl(123)).toBe(false);
+  expect(isShellControl("not json")).toBe(false);
+  expect(isShellControl(JSON.stringify({ origin: "x" }))).toBe(false);
+  expect(isShellControl(JSON.stringify({ type: 42 }))).toBe(false);
+});
+
+test("parseShellReadyOrigin extracts the origin from a ready message", () => {
+  expect(parseShellReadyOrigin(JSON.stringify({ type: "op-shell/ready", origin: "vscode-webview://x" }))).toBe(
+    "vscode-webview://x",
+  );
+  expect(parseShellReadyOrigin(JSON.stringify({ type: "op-shell/ready" }))).toBeUndefined();
+  expect(parseShellReadyOrigin(JSON.stringify({ type: "op-bridge/opened", generation: 1 }))).toBeUndefined();
+  expect(parseShellReadyOrigin("not json")).toBeUndefined();
+});
diff --git a/packages/op-vscode/src/vscode/shell-messages.ts b/packages/op-vscode/src/vscode/shell-messages.ts
new file mode 100644
index 000000000..59119d475
--- /dev/null
+++ b/packages/op-vscode/src/vscode/shell-messages.ts
@@ -0,0 +1,30 @@
+// Pure classification of the shell's control messages (op-shell/*). Kept
+// vscode-free and testable: a mis-classification here can drop a legitimate
+// snapshot whose docJson happens to contain the text "op-shell/", hanging the
+// save/backup that awaits it — so the match must be on the parsed top-level
+// `type`, never a substring of the raw payload.
+
+/** True only when `raw` is a JSON string whose top-level `type` is an
+ *  op-shell/* control type. Business messages (op-bridge/*) and any payload
+ *  that merely embeds "op-shell/" inside its data are NOT control traffic. */
+export function isShellControl(raw: unknown): boolean {
+  if (typeof raw !== "string") return false;
+  try {
+    const v = JSON.parse(raw) as { type?: unknown };
+    return typeof v.type === "string" && v.type.startsWith("op-shell/");
+  } catch {
+    return false;
+  }
+}
+
+/** The origin reported by an op-shell/ready control message, else undefined. */
+export function parseShellReadyOrigin(raw: unknown): string | undefined {
+  if (typeof raw !== "string") return undefined;
+  try {
+    const v = JSON.parse(raw) as { type?: unknown; origin?: unknown };
+    if (v.type === "op-shell/ready" && typeof v.origin === "string") return v.origin;
+  } catch {
+    /* not a control message */
+  }
+  return undefined;
+}