diff --git a/hive-c0re/src/lifecycle.rs b/hive-c0re/src/lifecycle.rs
index f8e4f1e..bdb0ffa 100644
--- a/hive-c0re/src/lifecycle.rs
+++ b/hive-c0re/src/lifecycle.rs
@@ -37,23 +37,30 @@ pub async fn spawn(name: &str, agent_flake: &str, agent_dir: &Path) -> Result<()
     validate(name)?;
     let container = container_name(name);
     run(&["create", &container, "--flake", agent_flake]).await?;
-    append_bind_flag(&container, agent_dir)?;
+    set_bind_flag(&container, agent_dir)?;
     run(&["start", &container]).await
 }
 
 /// `nixos-container` doesn't expose `--bind` on the CLI, but its start script
 /// expands `$EXTRA_NSPAWN_FLAGS` (from `/etc/nixos-containers/<name>.conf`)
-/// unquoted into the `systemd-nspawn` invocation. Append a `--bind` flag there.
-fn append_bind_flag(container: &str, agent_dir: &Path) -> Result<()> {
+/// unquoted into the `systemd-nspawn` invocation. Idempotently replace the
+/// `EXTRA_NSPAWN_FLAGS` line with the bind we want.
+fn set_bind_flag(container: &str, agent_dir: &Path) -> Result<()> {
     let path = format!("/etc/nixos-containers/{container}.conf");
-    let line = format!(
-        "\nEXTRA_NSPAWN_FLAGS=\"--bind={}:{CONTAINER_RUNTIME_MOUNT}\"\n",
+    let original = std::fs::read_to_string(&path).with_context(|| format!("read {path}"))?;
+    let mut lines: Vec<String> = original
+        .lines()
+        .filter(|line| !line.trim_start().starts_with("EXTRA_NSPAWN_FLAGS="))
+        .map(str::to_owned)
+        .collect();
+    lines.push(format!(
+        "EXTRA_NSPAWN_FLAGS=\"--bind={}:{CONTAINER_RUNTIME_MOUNT}\"",
         agent_dir.display()
-    );
-    let mut content = std::fs::read_to_string(&path).with_context(|| format!("read {path}"))?;
-    content.push_str(&line);
+    ));
+    let mut content = lines.join("\n");
+    content.push('\n');
     std::fs::write(&path, content).with_context(|| format!("write {path}"))?;
-    tracing::info!(%path, "appended EXTRA_NSPAWN_FLAGS for bind mount");
+    tracing::info!(%path, "set EXTRA_NSPAWN_FLAGS for bind mount");
     Ok(())
 }
 
@@ -63,10 +70,14 @@ pub async fn kill(name: &str) -> Result<()> {
     run(&["stop", &container]).await
 }
 
-pub async fn rebuild(name: &str, agent_flake: &str) -> Result<()> {
+pub async fn rebuild(name: &str, agent_flake: &str, agent_dir: &Path) -> Result<()> {
     validate(name)?;
     let container = container_name(name);
-    run(&["update", &container, "--flake", agent_flake]).await
+    set_bind_flag(&container, agent_dir)?;
+    run(&["update", &container, "--flake", agent_flake]).await?;
+    // Restart so any nspawn-level changes (bind mounts, networking, etc.) apply.
+    run(&["stop", &container]).await?;
+    run(&["start", &container]).await
 }
 
 pub async fn list() -> Result<Vec<String>> {
diff --git a/hive-c0re/src/server.rs b/hive-c0re/src/server.rs
index 131e1b4..487c92f 100644
--- a/hive-c0re/src/server.rs
+++ b/hive-c0re/src/server.rs
@@ -77,7 +77,8 @@ async fn dispatch(req: &HostRequest, agent_flake: &str, coord: &Coordinator) ->
             }
             HostRequest::Rebuild { name } => {
                 tracing::info!(%name, "rebuild");
-                lifecycle::rebuild(name, agent_flake).await?;
+                let agent_dir = Coordinator::agent_dir(name);
+                lifecycle::rebuild(name, agent_flake, &agent_dir).await?;
                 HostResponse::success()
             }
             HostRequest::List => HostResponse::list(lifecycle::list().await?),