diff --git a/py/api/__init__.py b/py/api/__init__.py
index 3948c905..64c2cad4 100644
--- a/py/api/__init__.py
+++ b/py/api/__init__.py
@@ -112,14 +112,15 @@ _STATIC_SEPARATORS = re.compile(r"[\\/]+")
 STATIC_EXACT_FILES = {("js", "inspection-semantics.json"): "application/json"}
 
 
-def _resolve_static_file(root, filepath):
+def _resolve_static_file(root, filepath, allowed=STATIC_MIME_TYPES):
     """Real path of ``filepath`` under ``root``, or None when it must not be served.
 
     The request path is untrusted. It is rejected when it is empty, carries a
     ``..`` segment, is absolute on any platform (a leading slash or backslash,
     a drive letter such as ``C:`` or a UNC ``\\\\server\\share`` prefix all
     re-anchor ``os.path.join`` on Windows), has an extension outside
-    STATIC_MIME_TYPES, or resolves (symlinks included) outside ``root``.
+    ``allowed`` (STATIC_MIME_TYPES), or resolves (symlinks included) outside
+    ``root``.
     """
     if not isinstance(filepath, str) or not filepath:
         return None
@@ -132,7 +133,7 @@ def _resolve_static_file(root, filepath):
     segments = _STATIC_SEPARATORS.split(filepath)
     if any(segment in ("", ".", "..") for segment in segments):
         return None
-    if os.path.splitext(filepath)[1].lower() not in STATIC_MIME_TYPES:
+    if os.path.splitext(filepath)[1].lower() not in allowed:
         return None
     try:
         root_real = Path(os.path.normcase(os.path.realpath(root)))
@@ -482,13 +483,14 @@ class PromptManagerAPI(
         """Serve ``web/<subdir>/<filepath>``; 403 outside it, 404 when missing."""
         root = os.path.join(_get_project_root(), "web", subdir)
         exact = STATIC_EXACT_FILES.get((subdir, filepath))
-        if exact is not None:
-            file_path, content_type = os.path.join(root, filepath), exact
-        else:
-            file_path = _resolve_static_file(root, filepath)
-            if file_path is None:
-                return web.Response(text="Forbidden", status=403)
-            content_type = STATIC_MIME_TYPES[os.path.splitext(file_path)[1].lower()]
+        # An exact file passes the same containment check, its extension only.
+        allowed = STATIC_MIME_TYPES if exact is None else {".json"}
+        file_path = _resolve_static_file(root, filepath, allowed)
+        if file_path is None:
+            return web.Response(text="Forbidden", status=403)
+        content_type = (
+            exact or STATIC_MIME_TYPES[os.path.splitext(file_path)[1].lower()]
+        )
         if not os.path.isfile(file_path):
             return web.Response(text="Not Found", status=404)
         with open(file_path, "rb") as f:
diff --git a/tests/test_api_core.py b/tests/test_api_core.py
index a8e0ee87..4af56a96 100644
--- a/tests/test_api_core.py
+++ b/tests/test_api_core.py
@@ -508,7 +508,7 @@ class TestStaticRoutes(CoreRoutesTestCase):
             "js/INSPECTION-SEMANTICS.json",
         ):
             resp = await self.client.request("GET", f"/prompt_manager/{path}")
-            self.assertIn(resp.status, (403, 404), path)
+            self.assertEqual(resp.status, 403, path)
 
     async def test_lib_served(self):
         web_dir = self._fake_root()
@@ -602,6 +602,28 @@ class TestStaticRoutes(CoreRoutesTestCase):
         resp = await self.client.request("GET", "/prompt_manager/lib/link.js")
         self.assertEqual(resp.status, 403)
 
+    async def test_inspection_semantics_symlink_escaping_web_dir_is_403(self):
+        """The exact-path JSON gets the same realpath containment as any file."""
+        web_dir = self._fake_root()
+        secret = Path(self.tmpdir) / "secret.json"
+        secret.write_text('{"secret": true}')
+        try:
+            os.symlink(secret, web_dir / "js" / "inspection-semantics.json")
+        except (OSError, NotImplementedError):
+            self.skipTest("symlinks not available")
+        resp = await self.client.request(
+            "GET", "/prompt_manager/js/inspection-semantics.json"
+        )
+        self.assertEqual(resp.status, 403)
+        self.assertNotIn("secret", await resp.text())
+
+    async def test_inspection_semantics_missing_is_404(self):
+        self._fake_root()
+        resp = await self.client.request(
+            "GET", "/prompt_manager/js/inspection-semantics.json"
+        )
+        self.assertEqual(resp.status, 404)
+
     async def test_empty_path_is_not_served(self):
         for prefix in ("lib", "js"):
             resp = await self.client.request("GET", f"/prompt_manager/{prefix}/")