composefs: Write /boot fstab entry during install

The composefs install path was missing the /boot entry in /etc/fstab,
causing the boot partition to not be mounted after reboot. This broke
`bootc status` and `bootc upgrade` on systems with a separate /boot
partition (e.g. `to-existing-root` installs).

The ostree path writes this entry in install_container(), but the
composefs path in setup_composefs_boot() did not. Write the /boot
fstab entry to the deployment's state etc directory after
write_composefs_state() creates it.

Closes: #2120
Assisted-by: Claude Code (Opus 4.6)
Signed-off-by: Xiaofeng Wang <henrywangxf@me.com>

Author: henrywang

crates/lib/src/bootc_composefs/boot.rs

@@ -1328,6 +1328,30 @@ pub(crate) async fn setup_composefs_boot(
     )
     .await?;
 
+    // Write the /boot entry to /etc/fstab in the deployment's state directory.
+    // This is needed so that systemd mounts the boot partition after reboot.
+    // The ostree path handles this in install_container(), but the composefs
+    // path was missing it.
+    if let Some(boot) = root_setup.boot.as_ref() {
+        if !boot.source.is_empty() {
+            let state_etc_path = root_setup
+                .physical_root_path
+                .join(crate::composefs_consts::STATE_DIR_RELATIVE)
+                .join(id.to_hex())
+                .join("etc");
+            let state_etc = Dir::open_ambient_dir(&state_etc_path, ambient_authority())
+                .with_context(|| format!("Opening {state_etc_path}"))?;
+            state_etc
+                .atomic_replace_with("fstab", |f| -> std::io::Result<_> {
+                    use std::io::Write;
+                    writeln!(f, "{}", boot.to_fstab())?;
+                    Ok(())
+                })
+                .context("Writing /boot entry to etc/fstab")?;
+            tracing::debug!("Wrote /boot fstab entry: {}", boot.to_fstab());
+        }
+    }
+
     Ok(())
 }
 

crates/lib/src/install.rs

@@ -1272,7 +1272,7 @@ pub(crate) struct RootSetup {
     pub(crate) rootfs_uuid: Option<String>,
     /// True if we should skip finalizing
     skip_finalize: bool,
-    boot: Option<MountSpec>,
+    pub(crate) boot: Option<MountSpec>,
     pub(crate) kargs: CmdlineOwned,
 }