CLI: fieldcraft-cli update --check | --install (#231)

--check runs app.update.check and prints its JSON; --install downloads the latest release for
this install, verifies the checksum list's signature and the asset's checksum, and swaps it in
(or, for .deb/.rpm, prints the package manager command for the verified download). Tested
against a local release server through FIELDCRAFT_UPDATE_HOST.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

apps/fieldcraft-cli/src/update.rs

@@ -0,0 +1,56 @@
+//! `fieldcraft-cli update --check | --install` (docs/updates.md): the same check as the app's
+//! Help › Check for Updates (`app.update.check`), and installing the latest release over this
+//! copy of the CLI's install, verified against the release key first. `FIELDCRAFT_UPDATE_HOST`
+//! points both at a local test server.
+
+use fieldcraft_engine::Session;
+use fieldcraft_update::install::{self, Finish};
+use fieldcraft_update::net::Client;
+use fieldcraft_update::stage::{self, Options};
+use serde_json::json;
+
+pub const USAGE: &str = "usage: fieldcraft-cli update --check | --install";
+
+pub fn run(args: &[String]) -> Result<(), String> {
+    match args.iter().map(String::as_str).collect::<Vec<_>>().as_slice() {
+        ["--check"] => check(),
+        ["--install"] => install(),
+        _ => Err(USAGE.into()),
+    }
+}
+
+fn check() -> Result<(), String> {
+    fieldcraft_engine::enable_update_checks(true);
+    let report = Session::default().execute("app.update.check", &json!({})).map_err(|e| e.to_string())?;
+    println!("{}", serde_json::to_string_pretty(&report).map_err(|e| e.to_string())?);
+    Ok(())
+}
+
+fn install() -> Result<(), String> {
+    let client = Client::from_env();
+    let check = client.check().map_err(|e| e.to_string())?;
+    if !check.newer() {
+        println!("FieldCraft {} is up to date (the latest release is {}).", check.current, check.latest.version);
+        return Ok(());
+    }
+    let here = install::here();
+    let downloads = fieldcraft_io::recovery::data_dir().map(|d| d.join("updates")).unwrap_or_else(|| std::env::temp_dir().join("fieldcraft-updates"));
+    eprintln!("Downloading FieldCraft {} for {}…", check.latest.version, here.describe());
+    let progress = |done: u64, total: u64| {
+        if total > 0 && done == total {
+            eprintln!("Downloaded {} MB; verifying…", total / (1024 * 1024));
+        }
+    };
+    let options = Options { key: fieldcraft_update::PUBLIC_KEY, downloads: &downloads, arch: std::env::consts::ARCH, progress: &progress };
+    let staged = stage::stage(&client, &check.latest, &here, &options).map_err(|e| e.to_string())?;
+    match install::plan(&staged, false).map_err(|e| e.to_string())? {
+        Finish::Swap(plan) => {
+            stage::apply(&plan).map_err(|e| e.to_string())?;
+            println!("Installed FieldCraft {} ({}). A running FieldCraft app uses it from its next start.", staged.version, here.describe());
+        }
+        Finish::Package { file, command } => {
+            println!("Downloaded and verified {}.\nInstall it with the system's package manager:\n  {command}", file.display());
+        }
+    }
+    Ok(())
+}