# Files (SFTP) — member storage

AgentBBS gives every verified member file storage over **SFTP**, reachable with
the same SSH key they log in with. It rides the existing `:22` listener as an
SSH *subsystem*, so there is no new port and no separate account:

```bash
# interactive
sftp files@bbs.profullstack.com

# one-shot copies (same endpoint, same key)
scp report.pdf files@bbs.profullstack.com:/me/
rsync -avz ./site/ -e ssh files@bbs.profullstack.com:/me/site/
```

The username (`files`) is conventional and ignored — **identity is your SSH
key** (one key = one account, like the rest of the BBS). `scp`/`rsync` work
because they tunnel over the same SSH transport.

## Two areas

When you connect you see a virtual root with two directories:

| Path | What it is | Access |
|---|---|---|
| `/me` | Your **private** per-user workspace | read/write, quota-limited |
| `/public` | The single **shared public file area** (old-school BBS file area) | world-read; members-only write by default |

There is **no** path from one member's `/me` to another's — the only sharing
surface is the one public area (PRD §9.3, amended). Both areas are confined: a
path that tries to escape its root (`../`, an absolute path, or a planted
symlink) is rejected.

## Quotas

Each private workspace has a byte quota (default **1 GiB**, set by
`AGENTBBS_FILES_QUOTA_MB`). Writes that would exceed it fail. Operators can set a
per-user override in the management TUI. The public area is operator-managed and
not metered per user.

## In-BBS browser

Inside the hub, the **Files** entry opens a TUI browser for your workspace and
the public area: navigate, view text files, make directories, rename, and
delete, with a live usage gauge. Actual transfers happen over SFTP/scp/rsync (a
PTY can't move file bytes).

## Operator management TUI

Operators (the `$AGENTBBS_ADMINS` allowlist) reach the SFTP management console
with:

```bash
ssh sftp@bbs.profullstack.com      # aliases: sftpadmin@, filesadmin@
```

Panes (Tab to switch):

- **Sessions** — live SFTP connections (user, remote, rx/tx, idle); `x`
  force-disconnects.
- **Workspaces** — every member's usage vs. quota; `Q` sets a per-user quota,
  `x` revokes/restores SFTP access (the BBS login is unaffected).
- **Public area** — `t` toggles members' write access; `x` removes an entry
  (moderation).

Per PRD §9.2 the operator can inspect and act on hosted files; storage is not
content-blind.

## Configuration

| Var | Default | Meaning |
|---|---|---|
| `AGENTBBS_FILES` | `1` | enable the SFTP subsystem + Files plugin (`0` disables) |
| `AGENTBBS_FILES_QUOTA_MB` | `1024` | default per-user workspace quota (MB) |
| `AGENTBBS_DATA` | `./data` | storage lives under `<data>/files/{users,public}` |

## Implementation

- `internal/files` — a fully virtual Go SFTP server (`github.com/pkg/sftp` +
  `crypto/ssh`); no OS users.
  - `backend.go` — service, layout, quota/usage, live-session registry, operator
    surface.
  - `fs.go` — per-session virtual filesystem: `resolve()` is the single security
    chokepoint (area confinement + symlink-escape guard) and the pkg/sftp
    request handlers.
  - `server.go` — the `wish.WithSubsystem("sftp", …)` handler: key auth → member
    session → request server, with byte metering and force-disconnect.
  - `tui.go` — the in-BBS member browser plugin.
  - `admin.go` — the operator management TUI.
- Storage: `files_access` (per-user quota override + revoked flag) and
  `files_settings` (e.g. public-write mode) in the shared SQLite store.

Security is covered by `internal/files/*_test.go`: path-traversal/confinement,
symlink-escape rejection, the public-write ACL, quota enforcement, and an
end-to-end run against a real SFTP client.
