build the app, and ship it on Linux and Windows as well as macOS

The client itself: the sync engine and mirror, the Gmail and IMAP providers,
the screener, the three boxes and two piles, compose and send, the sanitiser
and tracker stripping, contacts, clips, backup, notifications and the guide.

The pipeline that ships it. Three runners now build in parallel and the
publish gate wants all four platform keys in latest.json before a release
leaves draft. Linux gets two more packages Tauri does not build: a flatpak
repackaged from the deb against GNOME 48, and a Nix package that relinks the
deb against nixpkgs so it runs as a native Wayland client rather than through
Xwayland. CI runs the Rust suite on all three desktops rather than on Linux
alone, and rebuilds the flatpak manifest on every push to main.

Two things that were only ever exercised on macOS and were wrong everywhere
else. The menu bar was built by adjusting the submenus macOS is given, so on
a platform whose default menu has no File or View the new File menu landed
after Edit, Check for Updates landed nowhere, and the three places and the
reading pane had no menu at all. The deb declared libwebkit2gtk-4.1-0 and
libgtk-3-0 twice, because tauri.conf.json named the dependencies Tauri
already emits.

The updater key exists now, so releases can sign their artifacts.

src-tauri/Cargo.toml

@@ -30,7 +30,7 @@ sha2 = "0.10"
 rand = "0.8"
 url = "2"
 chrono = { version = "0.4", features = ["serde"] }
-tokio = { version = "1", features = ["sync", "time"] }
+tokio = { version = "1", features = ["sync", "time", "net", "io-util", "rt"] }
 
 # gzip because Gmail's JSON compresses by an order of magnitude and hydration is thousands of
 # responses; http2 because a batch of 50 and the poll loop share one connection.
@@ -69,6 +69,68 @@ bip39 = { version = "2.2", features = ["rand"] }
 # The system families the Appearance section offers alongside the six bundled ones.
 fontdb = "0.24"
 
+# The second provider: a mailbox reached over IMAP and SMTP with a password, which is every
+# account that is not Google. Proton is one of these, through Bridge on the loopback.
+#
+# `async-imap` defaults to async-std, so both its default features are off and the tokio pair is
+# named instead: there is one runtime in this process and it is Tauri's.
+async-imap = { version = "0.11", default-features = false, features = ["runtime-tokio", "tokio"] }
+# `async-imap` speaks futures-io and `tokio-rustls` speaks tokio-io, so the stream is bridged.
+tokio-util = { version = "0.7", features = ["compat"] }
+# `async-imap` returns its responses as futures streams, so the combinators come with it.
+futures = "0.3"
+
+# TLS for both, and the seam where a self-signed certificate is decided about.
+#
+# Every `ClientConfig` in this crate must name `rustls::crypto::ring::default_provider()`
+# explicitly. Both crypto providers are in the tree because of what reqwest pulls, so rustls has
+# no process default to fall back on and building a config without one panics at runtime rather
+# than failing to compile.
+tokio-rustls = { version = "0.26", default-features = false, features = ["ring", "tls12", "logging"] }
+rustls = { version = "0.23", default-features = false, features = ["ring", "std", "tls12", "logging"] }
+rustls-pki-types = "1"
+webpki-roots = "1"
+# The fingerprint shown in the certificate question, and the hostname check that decides whether
+# there is a question at all rather than a refusal.
+x509-parser = "0.18"
+
+# Sending. Same author as mail-parser and mail-builder, and pinned to ring for the same reason as
+# above. No `dkim`: nothing here signs outgoing mail.
+mail-send = { version = "0.6", default-features = false, features = ["ring", "tls12", "cram-md5", "digest-md5", "md5", "rand"] }
+
+# Autodiscovery. `hickory-resolver` is for the MX rung, which is what recognises a vanity domain
+# sitting on Google Workspace or Fastmail; `roxmltree` reads the clientConfig documents, which are
+# small, read-once and never written.
+hickory-resolver = { version = "0.26", default-features = false, features = ["system-config", "tokio"] }
+roxmltree = "0.21"
+
+# Notifications on macOS are posted through UserNotifications directly (notify/macos.rs says why the
+# plugin's own path shows nothing on macOS 26). These are the versions wry already resolves, so the
+# build keeps a single copy of objc2.
+[target.'cfg(target_os = "macos")'.dependencies]
+objc2 = "0.6"
+objc2-foundation = { version = "0.3", default-features = false, features = [
+  "std",
+  "NSDictionary",
+  "NSError",
+
+  "NSObject",
+  "NSString",
+] }
+objc2-user-notifications = { version = "0.3", default-features = false, features = [
+  "std",
+  "block2",
+  "UNUserNotificationCenter",
+  "UNNotification",
+  "UNNotificationContent",
+  "UNNotificationRequest",
+  "UNNotificationResponse",
+  "UNNotificationSettings",
+  "UNNotificationSound",
+  "UNNotificationTrigger",
+] }
+block2 = "0.6"
+
 # There is no auto-updater and no process to restart on a phone: the store is the update channel.
 [target.'cfg(not(any(target_os = "android", target_os = "ios")))'.dependencies]
 tauri-plugin-process = "2"