diff --git a/hatch_build.py b/hatch_build.py
index ffaa08f..cc52462 100644
--- a/hatch_build.py
+++ b/hatch_build.py
@@ -1,7 +1,7 @@
 """Hatch build hook to vendor CDN assets for offline use.
 
 During wheel builds, this hook:
-1. Parses base.html to find elements with data-vendor attributes
+1. Reads vendor-assets.json to find assets marked for vendoring
 2. Downloads each CDN asset to a temporary vendor directory
 3. Rewrites base.html to use local /static/vendor/ paths
 4. Fetches and bundles license information
@@ -13,6 +13,7 @@ distributed wheel has vendored assets.
 
 from __future__ import annotations
 
+import json
 import re
 import shutil
 import subprocess
@@ -23,22 +24,6 @@ from urllib.request import Request, urlopen
 
 from hatchling.builders.hooks.plugin.interface import BuildHookInterface
 
-# Matches elements with data-vendor attribute: extracts URL and target filename
-# Example: <script src="https://..." data-vendor="htmx.js">
-# Captures: (1) src/href, (2) URL, (3) attributes between, (4) vendor filename
-VENDOR_PATTERN = re.compile(r'(src|href)="(https://[^"]+)"([^>]*?)data-vendor="([^"]+)"')
-
-# License URLs for each package (GitHub raw URLs)
-LICENSE_URLS: dict[str, tuple[str, str]] = {
-    "htmx": ("MIT", "https://raw.githubusercontent.com/bigskysoftware/htmx/master/LICENSE"),
-    "xterm": ("MIT", "https://raw.githubusercontent.com/xtermjs/xterm.js/master/LICENSE"),
-    "daisyui": ("MIT", "https://raw.githubusercontent.com/saadeghi/daisyui/master/LICENSE"),
-    "tailwindcss": (
-        "MIT",
-        "https://raw.githubusercontent.com/tailwindlabs/tailwindcss/master/LICENSE",
-    ),
-}
-
 
 def _download(url: str) -> bytes:
     """Download a URL, trying urllib first then curl as fallback."""
@@ -61,7 +46,14 @@ def _download(url: str) -> bytes:
     return bytes(result.stdout)
 
 
-def _generate_licenses_file(temp_dir: Path) -> None:
+def _load_vendor_assets(root: Path) -> dict[str, Any]:
+    """Load vendor-assets.json from the web module."""
+    json_path = root / "src" / "compose_farm" / "web" / "vendor-assets.json"
+    with json_path.open() as f:
+        return json.load(f)
+
+
+def _generate_licenses_file(temp_dir: Path, licenses: dict[str, dict[str, str]]) -> None:
     """Download and combine license files into LICENSES.txt."""
     lines = [
         "# Vendored Dependencies - License Information",
@@ -73,7 +65,9 @@ def _generate_licenses_file(temp_dir: Path) -> None:
         "",
     ]
 
-    for pkg_name, (license_type, license_url) in LICENSE_URLS.items():
+    for pkg_name, license_info in licenses.items():
+        license_type = license_info["type"]
+        license_url = license_info["url"]
         lines.append(f"## {pkg_name} ({license_type})")
         lines.append(f"Source: {license_url}")
         lines.append("")
@@ -107,44 +101,57 @@ class VendorAssetsHook(BuildHookInterface):  # type: ignore[misc]
         if not base_html_path.exists():
             return
 
+        # Load vendor assets configuration
+        vendor_config = _load_vendor_assets(Path(self.root))
+        assets_to_vendor = vendor_config["assets"]
+
+        if not assets_to_vendor:
+            return
+
         # Create temp directory for vendored assets
         temp_dir = Path(tempfile.mkdtemp(prefix="compose_farm_vendor_"))
         vendor_dir = temp_dir / "vendor"
         vendor_dir.mkdir()
 
-        # Read and parse base.html
+        # Read base.html
         html_content = base_html_path.read_text()
+
+        # Build URL to filename mapping and download assets
         url_to_filename: dict[str, str] = {}
-
-        # Find all elements with data-vendor attribute and download them
-        for match in VENDOR_PATTERN.finditer(html_content):
-            url = match.group(2)
-            filename = match.group(4)
-
-            if url in url_to_filename:
-                continue
-
+        for asset in assets_to_vendor:
+            url = asset["url"]
+            filename = asset["filename"]
             url_to_filename[url] = filename
+            filepath = vendor_dir / filename
+            filepath.parent.mkdir(parents=True, exist_ok=True)
             content = _download(url)
-            (vendor_dir / filename).write_bytes(content)
+            filepath.write_bytes(content)
 
-        if not url_to_filename:
-            return
+        # Generate LICENSES.txt from the JSON config
+        _generate_licenses_file(vendor_dir, vendor_config["licenses"])
 
-        # Generate LICENSES.txt
-        _generate_licenses_file(vendor_dir)
+        # Rewrite HTML: replace CDN URLs with local paths and remove data-vendor attributes
+        # Pattern matches: src="URL" ... data-vendor="filename" or href="URL" ... data-vendor="filename"
+        vendor_pattern = re.compile(r'(src|href)="(https://[^"]+)"([^>]*?)data-vendor="([^"]+)"')
 
-        # Rewrite HTML to use local paths (remove data-vendor, update URL)
         def replace_vendor_tag(match: re.Match[str]) -> str:
             attr = match.group(1)  # src or href
             url = match.group(2)
             between = match.group(3)  # attributes between URL and data-vendor
-            filename = match.group(4)
             if url in url_to_filename:
+                filename = url_to_filename[url]
                 return f'{attr}="/static/vendor/{filename}"{between}'
             return match.group(0)
 
-        modified_html = VENDOR_PATTERN.sub(replace_vendor_tag, html_content)
+        modified_html = vendor_pattern.sub(replace_vendor_tag, html_content)
+
+        # Inject vendored mode flag for JavaScript to detect
+        # Insert right after <head> tag so it's available early
+        modified_html = modified_html.replace(
+            "<head>",
+            "<head>\n    <script>window.CF_VENDORED=true;</script>",
+            1,  # Only replace first occurrence
+        )
 
         # Write modified base.html to temp
         templates_dir = temp_dir / "templates"
diff --git a/src/compose_farm/web/cdn.py b/src/compose_farm/web/cdn.py
index 6b727ea..aedaa4c 100644
--- a/src/compose_farm/web/cdn.py
+++ b/src/compose_farm/web/cdn.py
@@ -1,78 +1,39 @@
 """CDN asset definitions and caching for tests and demo recordings.
 
-This module provides a single source of truth for CDN asset URLs used in
-browser tests and demo recordings. Assets are intercepted and served from
-a local cache to eliminate network variability.
+This module provides CDN asset URLs used in browser tests and demo recordings.
+Assets are intercepted and served from a local cache to eliminate network
+variability.
 
-Note: The canonical list of CDN assets for production is in base.html
-(with data-vendor attributes). This module includes those plus dynamically
-loaded assets (like Monaco editor modules loaded by app.js).
+The canonical list of CDN assets is in vendor-assets.json. This module loads
+that file and provides the CDN_ASSETS dict for test caching.
 """
 
 from __future__ import annotations
 
+import json
 import subprocess
-from typing import TYPE_CHECKING
+from pathlib import Path
+
+
+def _load_cdn_assets() -> dict[str, tuple[str, str]]:
+    """Load CDN assets from vendor-assets.json.
+
+    Returns:
+        Dict mapping URL to (filename, content_type) tuple.
+
+    """
+    json_path = Path(__file__).parent / "vendor-assets.json"
+    with json_path.open() as f:
+        config = json.load(f)
+
+    return {asset["url"]: (asset["filename"], asset["content_type"]) for asset in config["assets"]}
 
-if TYPE_CHECKING:
-    from pathlib import Path
 
 # CDN assets to cache locally for tests/demos
 # Format: URL -> (local_filename, content_type)
 #
-# If tests fail with "Uncached CDN request", add the URL here.
-CDN_ASSETS: dict[str, tuple[str, str]] = {
-    # From base.html (data-vendor attributes)
-    "https://cdn.jsdelivr.net/npm/daisyui@5/themes.css": ("daisyui-themes.css", "text/css"),
-    "https://cdn.jsdelivr.net/npm/daisyui@5": ("daisyui.css", "text/css"),
-    "https://cdn.jsdelivr.net/npm/@tailwindcss/browser@4": (
-        "tailwind.js",
-        "application/javascript",
-    ),
-    "https://cdn.jsdelivr.net/npm/@xterm/xterm@5.5.0/css/xterm.css": ("xterm.css", "text/css"),
-    "https://unpkg.com/htmx.org@2.0.4": ("htmx.js", "application/javascript"),
-    "https://cdn.jsdelivr.net/npm/@xterm/xterm@5.5.0/lib/xterm.js": (
-        "xterm.js",
-        "application/javascript",
-    ),
-    "https://cdn.jsdelivr.net/npm/@xterm/addon-fit@0.10.0/lib/addon-fit.js": (
-        "xterm-fit.js",
-        "application/javascript",
-    ),
-    "https://unpkg.com/idiomorph/dist/idiomorph.min.js": (
-        "idiomorph.js",
-        "application/javascript",
-    ),
-    "https://unpkg.com/idiomorph/dist/idiomorph-ext.min.js": (
-        "idiomorph-ext.js",
-        "application/javascript",
-    ),
-    # Monaco editor - dynamically loaded by app.js
-    "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/loader.js": (
-        "monaco-loader.js",
-        "application/javascript",
-    ),
-    "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/editor/editor.main.js": (
-        "monaco-editor-main.js",
-        "application/javascript",
-    ),
-    "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/editor/editor.main.css": (
-        "monaco-editor-main.css",
-        "text/css",
-    ),
-    "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/base/worker/workerMain.js": (
-        "monaco-workerMain.js",
-        "application/javascript",
-    ),
-    "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/basic-languages/yaml/yaml.js": (
-        "monaco-yaml.js",
-        "application/javascript",
-    ),
-    "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/base/browser/ui/codicons/codicon/codicon.ttf": (
-        "monaco-codicon.ttf",
-        "font/ttf",
-    ),
-}
+# If tests fail with "Uncached CDN request", add the URL to vendor-assets.json.
+CDN_ASSETS: dict[str, tuple[str, str]] = _load_cdn_assets()
 
 
 def download_url(url: str) -> bytes | None:
@@ -107,6 +68,7 @@ def ensure_vendor_cache(cache_dir: Path) -> Path:
         filepath = cache_dir / filename
         if filepath.exists():
             continue
+        filepath.parent.mkdir(parents=True, exist_ok=True)
         content = download_url(url)
         if not content:
             msg = f"Failed to download {url} - check network/curl"
diff --git a/src/compose_farm/web/static/app.js b/src/compose_farm/web/static/app.js
index ab4e8fd..c877c19 100644
--- a/src/compose_farm/web/static/app.js
+++ b/src/compose_farm/web/static/app.js
@@ -332,10 +332,14 @@ function loadMonaco(callback) {
     monacoLoading = true;
 
     // Load the Monaco loader script
+    // Use local paths when running from vendored wheel, CDN otherwise
+    const monacoBase = window.CF_VENDORED
+        ? '/static/vendor/monaco'
+        : 'https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs';
     const script = document.createElement('script');
-    script.src = 'https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/loader.js';
+    script.src = monacoBase + '/loader.js';
     script.onload = function() {
-        require.config({ paths: { vs: 'https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs' }});
+        require.config({ paths: { vs: monacoBase }});
         require(['vs/editor/editor.main'], function() {
             monacoLoaded = true;
             monacoLoading = false;
diff --git a/src/compose_farm/web/templates/base.html b/src/compose_farm/web/templates/base.html
index 09be520..7c75ebf 100644
--- a/src/compose_farm/web/templates/base.html
+++ b/src/compose_farm/web/templates/base.html
@@ -97,8 +97,8 @@
 
     <!-- Scripts - HTMX first -->
     <script src="https://unpkg.com/htmx.org@2.0.4" data-vendor="htmx.js"></script>
-    <script src="https://unpkg.com/idiomorph/dist/idiomorph.min.js"></script>
-    <script src="https://unpkg.com/idiomorph/dist/idiomorph-ext.min.js"></script>
+    <script src="https://unpkg.com/idiomorph/dist/idiomorph.min.js" data-vendor="idiomorph.js"></script>
+    <script src="https://unpkg.com/idiomorph/dist/idiomorph-ext.min.js" data-vendor="idiomorph-ext.js"></script>
     <script src="https://cdn.jsdelivr.net/npm/@xterm/xterm@5.5.0/lib/xterm.js" data-vendor="xterm.js"></script>
     <script src="https://cdn.jsdelivr.net/npm/@xterm/addon-fit@0.10.0/lib/addon-fit.js" data-vendor="xterm-fit.js"></script>
     <script src="/static/app.js"></script>
diff --git a/src/compose_farm/web/vendor-assets.json b/src/compose_farm/web/vendor-assets.json
new file mode 100644
index 0000000..d2cbcae
--- /dev/null
+++ b/src/compose_farm/web/vendor-assets.json
@@ -0,0 +1,122 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$comment": "CDN assets vendored into production builds and cached for tests",
+  "assets": [
+    {
+      "url": "https://cdn.jsdelivr.net/npm/daisyui@5",
+      "filename": "daisyui.css",
+      "content_type": "text/css",
+      "package": "daisyui"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/daisyui@5/themes.css",
+      "filename": "daisyui-themes.css",
+      "content_type": "text/css",
+      "package": "daisyui"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/@tailwindcss/browser@4",
+      "filename": "tailwind.js",
+      "content_type": "application/javascript",
+      "package": "tailwindcss"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/@xterm/xterm@5.5.0/css/xterm.css",
+      "filename": "xterm.css",
+      "content_type": "text/css",
+      "package": "xterm"
+    },
+    {
+      "url": "https://unpkg.com/htmx.org@2.0.4",
+      "filename": "htmx.js",
+      "content_type": "application/javascript",
+      "package": "htmx"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/@xterm/xterm@5.5.0/lib/xterm.js",
+      "filename": "xterm.js",
+      "content_type": "application/javascript",
+      "package": "xterm"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/@xterm/addon-fit@0.10.0/lib/addon-fit.js",
+      "filename": "xterm-fit.js",
+      "content_type": "application/javascript",
+      "package": "xterm"
+    },
+    {
+      "url": "https://unpkg.com/idiomorph/dist/idiomorph.min.js",
+      "filename": "idiomorph.js",
+      "content_type": "application/javascript",
+      "package": "idiomorph"
+    },
+    {
+      "url": "https://unpkg.com/idiomorph/dist/idiomorph-ext.min.js",
+      "filename": "idiomorph-ext.js",
+      "content_type": "application/javascript",
+      "package": "idiomorph"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/loader.js",
+      "filename": "monaco/loader.js",
+      "content_type": "application/javascript",
+      "package": "monaco-editor"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/editor/editor.main.js",
+      "filename": "monaco/editor/editor.main.js",
+      "content_type": "application/javascript",
+      "package": "monaco-editor"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/editor/editor.main.css",
+      "filename": "monaco/editor/editor.main.css",
+      "content_type": "text/css",
+      "package": "monaco-editor"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/base/worker/workerMain.js",
+      "filename": "monaco/base/worker/workerMain.js",
+      "content_type": "application/javascript",
+      "package": "monaco-editor"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/basic-languages/yaml/yaml.js",
+      "filename": "monaco/basic-languages/yaml/yaml.js",
+      "content_type": "application/javascript",
+      "package": "monaco-editor"
+    },
+    {
+      "url": "https://cdn.jsdelivr.net/npm/monaco-editor@0.52.2/min/vs/base/browser/ui/codicons/codicon/codicon.ttf",
+      "filename": "monaco/base/browser/ui/codicons/codicon/codicon.ttf",
+      "content_type": "font/ttf",
+      "package": "monaco-editor"
+    }
+  ],
+  "licenses": {
+    "htmx": {
+      "type": "MIT",
+      "url": "https://raw.githubusercontent.com/bigskysoftware/htmx/master/LICENSE"
+    },
+    "idiomorph": {
+      "type": "BSD-2-Clause",
+      "url": "https://raw.githubusercontent.com/bigskysoftware/idiomorph/main/LICENSE"
+    },
+    "xterm": {
+      "type": "MIT",
+      "url": "https://raw.githubusercontent.com/xtermjs/xterm.js/master/LICENSE"
+    },
+    "daisyui": {
+      "type": "MIT",
+      "url": "https://raw.githubusercontent.com/saadeghi/daisyui/master/LICENSE"
+    },
+    "tailwindcss": {
+      "type": "MIT",
+      "url": "https://raw.githubusercontent.com/tailwindlabs/tailwindcss/master/LICENSE"
+    },
+    "monaco-editor": {
+      "type": "MIT",
+      "url": "https://raw.githubusercontent.com/microsoft/monaco-editor/main/LICENSE.txt"
+    }
+  }
+}
diff --git a/tests/web/test_htmx_browser.py b/tests/web/test_htmx_browser.py
index 390c779..e1d0d9c 100644
--- a/tests/web/test_htmx_browser.py
+++ b/tests/web/test_htmx_browser.py
@@ -4,7 +4,7 @@ Run with: uv run pytest tests/web/test_htmx_browser.py -v --no-cov
 
 CDN assets are cached locally (in .pytest_cache/vendor/) to eliminate network
 variability. If a test fails with "Uncached CDN request", add the URL to
-compose_farm.web.cdn.CDN_ASSETS.
+src/compose_farm/web/vendor-assets.json.
 """
 
 from __future__ import annotations
@@ -90,7 +90,7 @@ def page(page: Page, vendor_cache: Path) -> Page:
                 return
         # Uncached CDN request - abort with helpful error
         route.abort("failed")
-        msg = f"Uncached CDN request: {url}\n\nAdd this URL to CDN_ASSETS in tests/web/test_htmx_browser.py"
+        msg = f"Uncached CDN request: {url}\n\nAdd this URL to src/compose_farm/web/vendor-assets.json"
         raise RuntimeError(msg)
 
     page.route(re.compile(r"https://(cdn\.jsdelivr\.net|unpkg\.com)/.*"), handle_cdn)