Folder drag/paste rejected in desktop thin-client mode even when the server runs on the same machine #27774

What happened

Using the desktop app as a thin client (Local environment off in desktop settings) connected to a t3 serve on the same machine (127.0.0.1), dragging a folder into the composer shows the toast "Folders can only be referenced in the local desktop environment". Clipboard-pasting a folder hits the same code path. Folder references would resolve fine because the connected environment shares the desktop's filesystem.

Diagnosis

addComposerFolders (apps/web/src/components/chat/ChatComposer.tsx, ~line 2673 in v0.1.3) calls folderDropTarget (apps/web/src/components/chat/folderDrop.ts):

if (
  input.localEnvironmentDisabled ||
  input.primaryEnvironmentId === null ||
  input.environmentId !== input.primaryEnvironmentId
) {
  return "remote";
}

localEnvironmentDisabled is window.desktopBridge.getLocalEnvironmentEnabled() === false (apps/web/src/localEnvironment.ts), reading the desktop setting localEnvironmentEnabled (apps/desktop/src/settings/DesktopAppSettings.ts). In "Desktop without a local environment" mode (docs/internals/remote.md) the setting is false and primaryEnvironmentId is null, so folder drops are unconditionally rejected. The gate is a proxy for "does this environment share the desktop's filesystem", but keys on "is this the app's own bundled environment" — a false positive for same-machine saved environments.

Verified on-machine: desktop-settings.json has "localEnvironmentEnabled":false; server on 127.0.0.1:3773 reports serverVersion 0.1.3, machine: "desktop". The gate is unchanged on current main, so v0.1.4/v0.1.5 are also affected.

Steps to reproduce

1. Turn off Local environment in desktop settings; connect to a t3 serve on the same machine (e.g. http://127.0.0.1:3773).
2. Drag a folder into the thread composer (or copy the folder and paste it).
3. Toast: "Folders can only be referenced in the local desktop environment"; nothing is inserted.

Version

0.1.3 (desktop app and server; also present in v0.1.5 and main)

Environment

Linux x64 (kernel 7.3.0), Node v24.22.1, desktop app 0.1.3 → server 0.1.3 at 127.0.0.1:3773

Evidence

~/.t3/userdata/desktop-settings.json: {"localEnvironmentEnabled":false,...}
GET /.well-known/t3/environment → "serverVersion":"0.1.3", "machine":"desktop"
Gate: apps/web/src/components/chat/folderDrop.ts (v0.1.3, identical on main)

Related issues

#26420 is the same thin-client mode but a different symptom ("No environment selected" in Sharing & access). Searched folder-drop/thin-client issues; none match.

Fix applied or workaround

None applied. Workaround: type the folder path with @ (resolves against the connected environment). Files still drag/paste fine (uploads).

Filed by

GLM (glm-5.3-flash) via t3 triage