Short answer: **stick with “file:// + blob workers” for now, fix your CSP, and switch from `getWorkerUrl` to `getWorker` on iOS/macOS.** Then, as a long‑term improvement, add a native `WKURLSchemeHandler` (macOS/iOS) and an optional tiny localhost server for dev.

Below is a concrete plan tailored to your codebase—with drop‑in patches you can apply right away.

---

## Why you’re seeing the warning

* You already inject a WKWebView worker shim in `monaco_assets.dart` that returns a **blob URL** from `getWorkerUrl(...)`.
* However, your current **CSP** disallows the worker’s `importScripts('file:///...')` network fetch because **`connect-src` is missing `file:`**. Safari/WKWebView treats `importScripts` as a network request governed by `connect-src`.
* Also, returning a *URL string* via `getWorkerUrl` leaves a few footguns on Safari. In practice, **returning a `Worker` instance** via `getWorker(...)` is more robust across WKWebView versions.

Result: creation of workers fails → Monaco falls back to executing worker code on the main thread → the warning.

---

## Minimal, safe fixes (now)

### 1) Widen your CSP for workers

In `MonacoAssets._generateIndexHtml(...)`, change your CSP meta to:

* add `blob:` to `script-src` (the worker’s bootstrap is a blob script),
* add `file:` to `connect-src` (so `importScripts('file:///...')` is allowed).

**Before (yours):**

```html
content="default-src 'self' file: 'unsafe-inline' 'unsafe-eval';
         script-src 'self' file: 'unsafe-inline' 'unsafe-eval';
         style-src 'self' 'unsafe-inline'${allowCdnFonts ? ' https:' : ''};
         font-src 'self' file: data:${allowCdnFonts ? ' https:' : ''};
         img-src 'self' data: blob: file:;
         worker-src 'self' blob:;
         connect-src 'self' blob:;"
```

**After (recommended):**

```html
content="default-src 'self' file: 'unsafe-inline' 'unsafe-eval';
         script-src 'self' file: blob: 'unsafe-inline' 'unsafe-eval';
         style-src 'self' 'unsafe-inline'${allowCdnFonts ? ' https:' : ''};
         font-src 'self' file: data:${allowCdnFonts ? ' https:' : ''};
         img-src 'self' data: blob: file:;
         worker-src 'self' blob:;
         connect-src 'self' blob: file:;"
```

> These two additions (`blob:` in `script-src` and `file:` in `connect-src`) are the usual missing pieces when Safari refuses to spin up blob workers that later `importScripts` from `file://`.

---

### 2) Use `getWorker(...)` instead of `getWorkerUrl(...)` on iOS/macOS

Replace the platform script you inject for `Platform.isIOS || Platform.isMacOS` with a **`getWorker`** version. This bypasses Monaco’s URL parsing code-path entirely and has proven to be the least brittle option on WKWebView.

**Patch for `monaco_assets.dart` → `_generateIndexHtml()` (iOS/macOS branch):**

```diff
-    // iOS and macOS need blob worker shim for WKWebView + file:// protocol
-    platformScript = '''
-<script>
-  (function () {
-    console.log('[Init] Setting up worker shim for WKWebView');
-    const vsRel = '$vsPath'; // e.g., "min/vs"
-    let absVs;
-    try { absVs = new URL(vsRel, window.location.href).toString(); }
-    catch (_) { absVs = vsRel; }
-
-    // Ensure baseUrl points to the ".../min/" folder (not ".../min/vs")
-    const idx = absVs.lastIndexOf('/vs');
-    const baseUrl = idx >= 0 ? absVs.substring(0, idx + 1) : absVs; // e.g., ".../min/"
-
-    // Set baseUrl so Monaco can resolve URLs before workers start
-    self.MonacoEnvironment = {
-      baseUrl: baseUrl,
-      getWorkerUrl: function (moduleId, label) {
-        // Include the label for better worker resolution and debugging
-        const src =
-          "self.MonacoEnvironment = { baseUrl: '" + baseUrl + "' };\n" +
-          "self.monacoLabel = '" + label + "';\n" +
-          "importScripts('" + absVs + "/base/worker/workerMain.js');\n";
-        return URL.createObjectURL(new Blob([src], { type: 'application/javascript' }));
-      }
-    };
-    console.log('[Init] Worker shim configured. baseUrl=' + baseUrl);
-  })();
-</script>
-''';
+    // iOS and macOS: robust blob-worker shim using getWorker (not getWorkerUrl)
+    platformScript = '''
+<script>
+  (function () {
+    console.log('[Init] Setting up worker shim for WKWebView');
+    const VS_REL = '$vsPath'; // usually "min/vs"
+    let VS_ABS;
+    try { VS_ABS = new URL(VS_REL, window.location.href).toString().replace(/\\/$/, ''); }
+    catch (_) { VS_ABS = VS_REL; }
+
+    // baseUrl must point to ".../min/" (one level up from ".../min/vs")
+    const BASE_URL = VS_ABS.replace(/\\/vs$/, '/') ;
+
+    self.MonacoEnvironment = {
+      baseUrl: BASE_URL,
+      getWorker: function (moduleId, label) {
+        const bootstrap =
+          "self.MonacoEnvironment = { baseUrl: '" + BASE_URL + "' };\\n" +
+          "self.MONACO_LABEL = '" + (label || '') + "';\\n" +
+          "importScripts('" + VS_ABS + "/base/worker/workerMain.js');\\n";
+        const blob = new Blob([bootstrap], { type: 'application/javascript' });
+        return new Worker(URL.createObjectURL(blob), { name: label });
+      }
+    };
+    console.log('[Init] Worker shim configured. baseUrl=' + BASE_URL);
+  })();
+</script>
+''';
```

**Why this helps**

* `getWorker(...)` returns an actual `Worker` object; Monaco won’t try to parse a URL against a possibly `null` base.
* The worker bootstrap sets `MonacoEnvironment.baseUrl` **inside the worker** too and loads `workerMain.js` with an absolute **`file:///.../min/vs/...`** URL.
* With the CSP tweak, Safari now allows that `importScripts` call.

---

### 3) (Optional) Set `baseUrl` everywhere for consistency

For Windows/Linux you can also set `MonacoEnvironment.baseUrl` early (harmless and sometimes useful for relative resolves):

```diff
-    } else {
-      // Linux and other platforms: just set baseUrl
-      final baseUrl = vsPath.replaceAll('/vs', '/');
-      platformScript = '''
+    } else {
+      // Linux/Other (and OK for Windows if you want consistency): set baseUrl
+      final baseUrl = vsPath.replaceAll('/vs', '/');
+      platformScript = '''
 <script>
   // Linux/Other: Set Monaco base URL for worker/resource resolution
   console.log('[Init] Setting Monaco base URL');
   self.MonacoEnvironment = { baseUrl: '$baseUrl' };
 </script>
 ''';
```

(Windows generally works from `file://` without extra help, but it doesn’t hurt.)

---

## Smoke test (what you should see)

* The two console warnings disappear:

  * `Could not create web worker(s)...`
  * `"...workerMain.js#editorWorkerService" cannot be parsed as a URL against "null".`
* Tokenization and heavy IntelliSense feel smoother (no main‑thread jank).
* In the console, you’ll see your `[Init] Worker shim configured...` log but **no fallback** messages from Monaco.

---

## Longer‑term improvements (nice to have)

1. **`WKURLSchemeHandler` (macOS/iOS):**
   Serve `vs/` from a custom origin (e.g., `monaco://vs/...`) and set:

   ```js
   self.MonacoEnvironment = { baseUrl: 'monaco:///' };
   ```

   Workers can then load `monaco:///vs/base/worker/workerMain.js` as same‑origin.
   *Pros:* no blobs, best performance, clean URLs.
   *Cons:* small amount of native code in the plugin.

2. **Tiny local HTTP server (dev‑only mode):**
   Use `package:shelf` + `shelf_static` to serve the extracted `min/vs` folder on `127.0.0.1:<port>` and load `http://127.0.0.1:<port>/index.html`.
   *Pros:* dead simple; avoids file:// quirks.
   *Cons:* ATS exceptions on iOS, less ideal for a packaged desktop app.

If you want, I can sketch the `WKURLSchemeHandler` registration (Obj‑C/Swift) and the Dart side to flip between **`file://` (default)**, **`scheme://` (best for Apple)**, and **`http://127.0.0.1` (dev)** with a single enum in your plugin options.

---

## TL;DR recommendation

* **Do now:** update CSP (`script-src` add `blob:`, `connect-src` add `file:`) and switch the WKWebView shim to **`getWorker`**.
* **Do next:** add a `WKURLSchemeHandler` path as the **premium solution** for macOS/iOS; keep the blob‑worker path as a fallback.
* **Optional (dev):** add a tiny localhost server toggle.
