fix(security): restart a companion whose image was rebuilt underneath it

A rebuilt image never reached a running companion. ensure_image_present
rebuilds in place under the same tag, so the quadlet body is identical,
write_if_changed reports no change, and enable_now is a no-op on a running
service — the container keeps the old layers indefinitely.

That is precisely how archi-dev-box kept serving the LND, FIPS, Electrs and
Guardian screens on 0.0.0.0 after v1.7.123 rebuilt every one of those images
to bind loopback: correct images on disk, three-day-old containers still
running. Closing those ports needed a manual 'podman rm -f' per container,
which no other node would ever get. Compare the running container's image ID
against the built one and restart when they diverge.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/container/companion.rs

@@ -214,10 +214,59 @@ pub async fn install_one(spec: &CompanionSpec) -> Result<()> {
     }
     // Start is idempotent — if already running, systemctl returns 0.
     quadlet::enable_now(&unit.service_name()).await?;
+
+    // A rebuilt image does NOT reach a container that is already running.
+    // `ensure_image_present` rebuilds in place under the same tag, so the unit
+    // body is byte-identical, `write_if_changed` reports no change, and
+    // `enable_now` is a no-op on a running service — the container keeps the
+    // old layers indefinitely. That is exactly how archi-dev-box kept serving
+    // the LND, FIPS, Electrs and Guardian screens on 0.0.0.0 after v1.7.123
+    // rebuilt every one of those images to bind loopback: the images were
+    // correct on disk and the running containers were three days old
+    // (2026-08-05). Compare image IDs and restart when they diverge.
+    if let Some(running) = container_image_id(spec.name).await {
+        if let Some(built) = image_id(&image).await {
+            if running != built {
+                info!(
+                    companion = spec.name,
+                    "running container uses a stale image; restarting onto the rebuilt one"
+                );
+                quadlet::restart_service(&unit.service_name()).await?;
+            }
+        }
+    }
     info!(companion = spec.name, "companion started");
     Ok(())
 }
 
+/// Image ID a container is actually running, or `None` when it does not exist.
+async fn container_image_id(name: &str) -> Option<String> {
+    let out = tokio::process::Command::new("podman")
+        .args(["inspect", name, "--format", "{{.Image}}"])
+        .output()
+        .await
+        .ok()?;
+    if !out.status.success() {
+        return None;
+    }
+    let id = String::from_utf8_lossy(&out.stdout).trim().to_string();
+    (!id.is_empty()).then_some(id)
+}
+
+/// Current ID behind an image reference, or `None` when absent.
+async fn image_id(image_ref: &str) -> Option<String> {
+    let out = tokio::process::Command::new("podman")
+        .args(["image", "inspect", image_ref, "--format", "{{.Id}}"])
+        .output()
+        .await
+        .ok()?;
+    if !out.status.success() {
+        return None;
+    }
+    let id = String::from_utf8_lossy(&out.stdout).trim().to_string();
+    (!id.is_empty()).then_some(id)
+}
+
 /// Build companion image locally if a Dockerfile exists, otherwise
 /// pull from the lfg2025 registry. Returns the image ref the quadlet
 /// should reference (`localhost/<base>:latest` for build, registry