A minimalist desktop client for [Smol Mail](../smolmail): one compact window — the list above, the article below — built on [fumi-core](../fumi), the reference CLI's own library, with a [Relm4](https://relm4.org) (GTK4) UI built from libadwaita's own widgets, so it follows the user's theme and accent colour. One 32-byte seed is the only secret; mail stays sealed at rest and opens on demand.
- Composes closed by any sidebar trip are stashed as drafts — kept beside the store, reopened from a folder that appears only once one exists; Cancel is the only way to throw one away.
- Custom `Key: value` frontmatter rows when writing: one line per header under the subject, validated against the frontmatter rules — the client's own fields (subject, reply-to, in-reply-to, accept) can't be shadowed, and rows survive a stash as part of the draft. Received mail shows the sender's own fields in the message detail, between the meta line and the body; replying to such a mail asks whether to carry copies of the fields into the reply, where they stay editable.
- Contacts with verified/tofu marks and smol:// import; each contact's detail names the server its address lives on and whether that server's key is pinned, with a pin action when it is not. Your own identity opens in the same detail view, its address in the header bar with a QR share beside it, key, fingerprint and URI below.
- Optional strict first contact: writing to someone new whose address carries no key means their key has to be looked up on their own server, and an unpinned server can answer with one of its own. With the setting on, that send stops and the compose offers to fetch and pin the server's key first, so it can be checked against what the operator published. A smol:// address whose key differs from the one already on file asks before replacing it, either way.
- Key rotation with a confirm-first step, a network timeout, gsmol backup export/import that never contains the seed, and a log-out that erases the local files and returns to onboarding. Preferences live in a plaintext sidecar beside the store, so they survive a restart.
Everything lives under `$XDG_CONFIG_HOME/carrier` (default `~/.config/carrier`): `carrier.key` is the master seed, written 0600; `carrier.db` is fumi-core's sealed store; `read.txt` is carrier's own read marks, one hex id per line; `settings.txt` holds the preferences as one `key value` line each.
The tests run offline against an in-memory store: seed and key parsing, a sealed envelope listed and opened end to end, contact import, a full backup round-trip, pin labels and the date formatter. `scripts/devbox-libs.sh` puts the GUI stack's runtime libraries (wayland, xkbcommon, EGL, vulkan) on the library path inside the devbox shell — they are dlopened, so nothing that links the binary can provide them.
## Status
Work in progress: the UI is unexercised against a live server — the store, crypto and address paths are covered by tests, the network flows (register, fetch, send, rotate) are wired to fumi-core's operations but only smoke-tested as far as launching the window.
