[BUG] SendUserFile never delivers files from sessions a `claude remote-control` server spawns

What's wrong

In a session spawned by claude remote-control, every SendUserFile call returns not delivered: this session is not on a project thread, so it has nowhere to place a file. The card still shows up in the iOS app, but it's greyed out and won't open. It happens for any file, including a small PNG at the root of the session's own worktree.

From reading the 2.1.280 bundle, it looks like the upload lane selector never picks a route for these sessions. The spawned child gets CLAUDE_CODE_ENVIRONMENT_KIND=bridge, replBridgeEnabled is false, and none of CLAUDE_CODE_BRIEF_UPLOAD, CLAUDE_CODE_REMOTE_ENVIRONMENT_TYPE or CLAUDE_CODE_REMOTE is set, so the lane is none. A terminal session with /remote-control turned on gets the repl lane and uploads fine.

What should happen

A file sent from a server-spawned session should upload and open in the app, the same as from a terminal session with Remote Control on. The tools reference says SendUserFile is available whenever a Remote Control client is connected.

Steps to reproduce

1. In a git repo, run claude remote-control --spawn worktree.
2. Start a new session on that environment from the iOS app.
3. Ask Claude to send any image in the working directory with SendUserFile.
4. The tool result says "not delivered", and the card in the app is greyed out.

Error

1 file could NOT be delivered to the user:
  <worktree>/test.png (0.0 MiB): not delivered: this session is not on a project thread, so it has nowhere to place a file

Workaround

Setting CLAUDE_CODE_BRIEF_UPLOAD=1 in the server's environment moves spawned sessions to the env_brief_upload lane. The file uploads and opens on iOS. It isn't documented, so I'd rather not depend on it.

Related

#90455 looks adjacent (cards that report success but break when the source path goes away). Separately, when a client asks the session for a file that wasn't uploaded, readFileForRemote refuses any real path outside the session's start directory (read denied: <path>), so files in temp or scratchpad directories can't be opened that way either.

Environment

• Claude Code 2.1.280
• macOS, server run under launchd
• claude.ai login (Anthropic API)
• Regression: don't know
• Model: not model-specific