release(v1.7.8-alpha): fix apply ETXTBSY — use mv instead of install

apply_update's binary swap called `sudo install -m 0755 src
/usr/local/bin/archipelago`. install opens the destination for write
with O_TRUNC; the kernel returns ETXTBSY (exit 1) when the path is a
currently-running executable, which it always is during apply because
apply_update is called by the archipelago RPC handler — running as
archipelago itself. Every previous "Failed to apply update" was this
one root cause; the manual sideload path only worked because we
stopped the service first.

rename() doesn't modify the file it replaces — it repoints the path
at a new inode while the old inode stays alive for any process that
has it mapped. `mv` uses rename(). Switched to `sudo mv` (with prior
chmod+chown on the staging file) so the swap is atomic and tolerant
of the running binary.

Frontend tarball byte-identical to v1.7.7-alpha; only the binary
version string changes.

Artefacts:
  archipelago                                      2753daec…48094d  40377648
  archipelago-frontend-1.7.8-alpha.tar.gz          4fb79664…0172e9  76984615 (reused)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/Cargo.lock

@@ -80,7 +80,7 @@ checksum = "a23eb6b1614318a8071c9b2521f36b424b2c83db5eb3a0fead4a6c0809af6e61"
 
 [[package]]
 name = "archipelago"
-version = "1.7.6-alpha"
+version = "1.7.8-alpha"
 dependencies = [
  "anyhow",
  "archipelago-container",

core/archipelago/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "archipelago"
-version = "1.7.6-alpha"
+version = "1.7.8-alpha"
 edition = "2021"
 description = "Archipelago Bitcoin Node OS - Native backend"
 authors = ["Archipelago Team"]

core/archipelago/src/update.rs

@@ -277,27 +277,31 @@ pub async fn apply_update(data_dir: &Path) -> Result<()> {
 
         match name.as_str() {
             "archipelago" => {
-                // /usr/local/bin is root-owned; archipelago user can't
-                // fs::copy into it directly. Use sudo install which handles
-                // the copy, mode, and ownership atomically.
+                // We're running FROM /usr/local/bin/archipelago right now,
+                // so we can't rewrite it in place — `install` / `cp` would
+                // hit ETXTBSY on the busy executable. Use `mv` instead:
+                // rename() is atomic and doesn't modify the existing file,
+                // it just re-points the path at a new inode. The currently
+                // running process keeps executing off the old inode; new
+                // invocations (i.e. after the post-apply systemctl
+                // restart) pick up the new binary.
+                let staged = src.to_string_lossy().to_string();
+                let _ = tokio::process::Command::new("sudo")
+                    .args(["chmod", "0755", &staged])
+                    .status()
+                    .await;
+                let _ = tokio::process::Command::new("sudo")
+                    .args(["chown", "root:root", &staged])
+                    .status()
+                    .await;
                 let status = tokio::process::Command::new("sudo")
-                    .args([
-                        "install",
-                        "-m",
-                        "0755",
-                        "-o",
-                        "root",
-                        "-g",
-                        "root",
-                        &src.to_string_lossy(),
-                        "/usr/local/bin/archipelago",
-                    ])
+                    .args(["mv", &staged, "/usr/local/bin/archipelago"])
                     .status()
                     .await
-                    .with_context(|| format!("Failed to spawn install for {}", name))?;
+                    .with_context(|| format!("Failed to spawn mv for {}", name))?;
                 if !status.success() {
                     anyhow::bail!(
-                        "sudo install failed for {} (exit {:?})",
+                        "sudo mv failed for {} (exit {:?})",
                         name,
                         status.code()
                     );