📁 SFTP server (daemon)

📌 Description

A built-in SFTP server with per-application isolation: a user gets access to the files of a specific application, not the whole server — their own SFTP client (FileZilla, WinSCP, sftp), not a browser tab. This is a different feature from the platform UI's file manager, which browses a whole node's filesystem through the daemon's FileService.

🎯 Scenarios

• 🔧 A developer connects FileZilla to sftp://node:2022 with credentials issued by the platform and sees only their application's directory.
• 🎮 A game designer uploads mods to a game server without OS access.

🏗️ Technical design

• Server: a built-in SSH/SFTP subsystem in Rust (russh), a separate port (2022 by default), no OS system users.
• Isolation: a virtual chroot onto the application directory (volumes for Docker, the working directory for native apps); path traversal is ruled out at the path-resolver level.
• Accounts: temporary credentials/keys are issued by the platform with a user → application → permissions (ro/rw) binding; TTL and revocation.
• Permissions: granting SFTP access is the apps.files permission (🔐 access-control).
• Quotas and limits: upload size and speed limits — per plan/config.
• Audit: a log of sessions and write operations.

🔗 Related tasks

DMN-010 in ROADMAP.md.