diff --git a/.github/workflows/test-frontend.yaml b/.github/workflows/test-frontend.yaml
index 8327c07..1d11d2e 100644
--- a/.github/workflows/test-frontend.yaml
+++ b/.github/workflows/test-frontend.yaml
@@ -5,6 +5,8 @@ on:
             - "src/**"
             - "package.json"
             - "tsconfig.json"
+            - "vite.config.ts"
+            - "package-lock.json"
 
 jobs:
     test:
@@ -55,3 +57,20 @@ jobs:
                   cache: npm
             - run: npm ci
             - run: npm run build
+            # Vite's esbuild pre-bundling can inject __publicField helper calls
+            # into maplibre-gl, breaking its Web Worker blob creation at runtime.
+            # Setting build.target and optimizeDeps.esbuildOptions.target to es2022+
+            # in vite.config.ts prevents this by using native class fields instead.
+            # This step catches regressions from config changes, Vite/esbuild upgrades,
+            # or new dependencies that might reintroduce the problem.
+            # This check can be removed once maplibre-gl no longer creates Web Workers
+            # from inline blobs, or once Vite drops esbuild pre-bundling entirely.
+            # See https://github.com/tmshv/sphere/issues/102
+            - name: Check for __publicField regression
+              run: |
+                  if grep -r '__publicField' dist/assets/*.js; then
+                      echo "ERROR: __publicField found in build output."
+                      echo "Ensure build.target and optimizeDeps.esbuildOptions.target"
+                      echo "are set to es2022 or higher in vite.config.ts."
+                      exit 1
+                  fi
diff --git a/CLAUDE.md b/CLAUDE.md
index 6690fb1..6146a2d 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -107,6 +107,10 @@ Available Tauri commands (invoked from frontend via `invoke()`):
 | `mbtiles_get_metadata` | Get MBTiles metadata/TileJSON |
 | `show_in_finder` | Open file location in system explorer |
 
+## Important Build Constraints
+
+**esbuild target must be es2022+**: Both `build.target` and `optimizeDeps.esbuildOptions.target` in `vite.config.ts` must remain `es2022` or higher. Lower targets cause esbuild to inject `__publicField` helper calls into `maplibre-gl`, breaking its Web Worker blob creation at runtime. `tsconfig.json` `useDefineForClassFields` must stay `false` to match. CI checks the build output for this regression. Future versions of maplibre-gl may fix the inline blob worker approach, making this constraint unnecessary — check when upgrading. See [#102](https://github.com/tmshv/sphere/issues/102).
+
 ## Known Issues / Technical Debt
 
 1. **Error handling** - Error types discard context (e.g., `From<io::Error>` returns generic variant without details)
diff --git a/tsconfig.json b/tsconfig.json
index 0caa506..fdc7c58 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -2,10 +2,10 @@
     "compilerOptions": {
         "baseUrl": "./",
         "paths": {
-            "@/*": ["src/*"]
+            "@/*": ["src/*"],
         },
-        "target": "ESNext",
         "useDefineForClassFields": true,
+        "target": "ES2022",
         "lib": ["DOM", "DOM.Iterable", "ESNext"],
         "allowJs": false,
         "skipLibCheck": true,
@@ -19,7 +19,7 @@
         "isolatedModules": true,
         "noEmit": true,
         "types": ["vitest/globals"],
-        "jsx": "react-jsx"
+        "jsx": "react-jsx",
     },
-    "include": ["src"]
+    "include": ["src"],
 }
diff --git a/vite.config.ts b/vite.config.ts
index a8451cc..06befb2 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -37,9 +37,14 @@ export default defineConfig({
     // to make use of `TAURI_DEBUG` and other env variables
     // https://tauri.studio/v1/api/config#buildconfig.beforedevcommand
     envPrefix: ["VITE_", "TAURI_"],
+    optimizeDeps: {
+        esbuildOptions: {
+            target: "es2022",
+        },
+    },
     build: {
         // Tauri supports es2021
-        target: ["es2021", "chrome100", "safari13"],
+        target: ["es2022", "safari15"],
         // don't minify for debug builds
         minify: !process.env.TAURI_DEBUG ? "esbuild" : false,
         // produce sourcemaps for debug builds