diff --git a/src/langbot/pkg/api/http/controller/groups/plugins.py b/src/langbot/pkg/api/http/controller/groups/plugins.py
index 4bce79869..950a8954d 100644
--- a/src/langbot/pkg/api/http/controller/groups/plugins.py
+++ b/src/langbot/pkg/api/http/controller/groups/plugins.py
@@ -165,6 +165,16 @@ except Exception:
     pass
 
 
+def _is_plugin_not_installed(exc: BaseException) -> bool:
+    """True when the connector reports a plugin absent from the resolved Workspace.
+
+    The connector raises a plain ``ValueError`` for this case, so resource routes
+    answer 404 instead of surfacing a 500 the WebUI would have to swallow.
+    """
+
+    return 'is not installed in this workspace' in str(exc).lower()
+
+
 def _normalize_plugin_asset_path(filepath: str) -> str | None:
     filepath = filepath.replace('\\', '/')
     if filepath.startswith('/'):
@@ -596,7 +606,15 @@ class PluginsRouterGroup(group.RouterGroup):
             request_context: RequestContext,
         ) -> quart.Response:
             await self._require_authenticated_plugin_runtime_context(request_context)
-            icon_data = await self.ap.plugin_connector.get_plugin_icon(author, plugin_name)
+            try:
+                icon_data = await self.ap.plugin_connector.get_plugin_icon(author, plugin_name)
+            except ValueError as exc:
+                # A plugin that is not installed for this Workspace is a missing
+                # resource, not a server fault: the WebUI asks for icons by plugin
+                # identity and must be able to fall back silently.
+                if _is_plugin_not_installed(exc):
+                    return quart.Response('Icon not found', status=404)
+                raise
             icon_bytes = await asyncio.to_thread(base64.b64decode, icon_data['plugin_icon_base64'])
             return quart.Response(icon_bytes, mimetype=icon_data['mime_type'])
 
diff --git a/tests/unit_tests/plugin/test_plugin_file_transfer_root.py b/tests/unit_tests/plugin/test_plugin_file_transfer_root.py
new file mode 100644
index 000000000..fad2751ba
--- /dev/null
+++ b/tests/unit_tests/plugin/test_plugin_file_transfer_root.py
@@ -0,0 +1,51 @@
+"""The host must share the Runtime's plugin file-transfer root in shared deployments.
+
+A mismatch leaves plugin icons and assets failing with
+"Invalid file transfer capability" because the SDK binds one directory inode per
+process (mode 0700) and picks the default from the runtime profile.
+"""
+
+from __future__ import annotations
+
+import os
+from importlib import import_module
+from types import SimpleNamespace
+
+from langbot_plugin.runtime.io.handler import SHARED_WORKER_FILE_STORAGE_DIR
+from langbot_plugin.runtime.security import PLUGIN_FILE_STORAGE_DIR_ENV
+
+
+def connector_module():
+    import_module('langbot.pkg.core.app')
+    return import_module('langbot.pkg.plugin.connector')
+
+
+def align(profile: str) -> None:
+    connector = connector_module()
+    connector.PluginRuntimeConnector._align_plugin_file_transfer_root(
+        SimpleNamespace(runtime_profile=profile)
+    )
+
+
+def test_shared_profile_pins_the_runtime_transfer_root(monkeypatch):
+    monkeypatch.delenv(PLUGIN_FILE_STORAGE_DIR_ENV, raising=False)
+
+    align('shared')
+
+    assert os.environ[PLUGIN_FILE_STORAGE_DIR_ENV] == SHARED_WORKER_FILE_STORAGE_DIR
+
+
+def test_explicit_operator_value_is_never_overridden(monkeypatch):
+    monkeypatch.setenv(PLUGIN_FILE_STORAGE_DIR_ENV, '/var/lib/custom-transfer')
+
+    align('shared')
+
+    assert os.environ[PLUGIN_FILE_STORAGE_DIR_ENV] == '/var/lib/custom-transfer'
+
+
+def test_oss_profile_leaves_the_default_alone(monkeypatch):
+    monkeypatch.delenv(PLUGIN_FILE_STORAGE_DIR_ENV, raising=False)
+
+    align('oss_dev')
+
+    assert PLUGIN_FILE_STORAGE_DIR_ENV not in os.environ