Fix btrfs-subvolume install aborting at 99% after root GPT retag

CHANGELOG.md

@@ -11,6 +11,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - **Signed OCI exports**: Drop source transport signatures when exporting a
   composefs image to a local OCI layout, which cannot store them.
+- **btrfs subvolume install: hostname/flatpak post-steps failed**: On btrfs
+  installs with subvolumes, retagging the root partition for GPT auto-discovery
+  remounted the root partition without `subvol=@`, exposing the btrfs top-level
+  instead of the `@` subvolume. Post-install steps that write through
+  `state/deploy` (hostname, system Flatpaks) then failed with
+  "finding composefs deploy etc: reading composefs deploy base …/state/deploy:
+  no such file or directory", aborting the install at 99%. The remount now
+  reuses the `subvol=@,compress=zstd:1` options via the new
+  `disk.BtrfsRootMountOpts` constant.
 - **OCI layout for non-composefs installs**: Non-composefs images (bluefin, lts,
   lts-hwe) now export to an OCI layout at scratch and use `--source-imgref oci:...`
   for `bootc install to-filesystem`. The previous VFS squash path corrupted ostree

fisherman/cmd/fisherman/main.go

@@ -922,8 +922,12 @@ func main() {
 		if err := os.MkdirAll(activeTargetMount, 0o755); err != nil {
 			fatal("recreating target mountpoint before remount: %v", err)
 		}
-		rootPart := disk.PartName(r.Disk, 2)
-		if err := disk.Mount(rootPart, activeTargetMount, ""); err != nil {
+		// Preserve the btrfs subvolume layout: SetupBtrfsSubvolumes mounted the
+		// target with subvol=@, and post-install steps (hostname, flatpaks) write
+		// through state/deploy inside that subvolume. Remounting without subvol=@
+		// would expose the btrfs top-level instead, where state/deploy does not
+		// exist, causing "finding composefs deploy etc" to fail.
+		if err := disk.RemountRoot(r.Disk, 2, activeTargetMount, r.BtrfsSubvolumes); err != nil {
 			fatal("remounting root partition after retagging: %v", err)
 		}
 		// Remount EFI so that Plymouth/LUKS arg writes land on the real ESP

fisherman/internal/disk/format.go

@@ -10,6 +10,13 @@ import (
 	"github.com/tuna-os/fisherman/internal/runner"
 )
 
+// BtrfsRootMountOpts are the mount options used for the root btrfs subvolume
+// layout (@, @home, @snapshots). The installed system's state/deploy tree lives
+// inside the @ subvolume, so any (re)mount of the root partition that post-install
+// steps write through must use these options; a bare mount would expose the
+// btrfs top-level instead, where state/deploy does not exist.
+const BtrfsRootMountOpts = "subvol=@,compress=zstd:1"
+
 // FormatEFI formats a partition as FAT32 for use as the EFI System Partition.
 func FormatEFI(part string) error {
 	return runner.Run("mkfs.fat", "-F32", "-n", "EFI-SYSTEM", part)
@@ -89,6 +96,22 @@ func Mount(dev, target, opts string) error {
 	return nil
 }
 
+// RemountRoot remounts the root partition (partition partNum of diskDev) at
+// target after an operation that dropped the mount, such as retagging the root
+// GPT type for systemd-boot GPT auto-discovery.
+//
+// When the install uses btrfs subvolumes, the root must be remounted with
+// subvol=@ so that post-install writes land inside the @ subvolume where the
+// composefs deployment (state/deploy) lives. A bare remount would expose the
+// btrfs top-level instead, where state/deploy does not exist.
+func RemountRoot(diskDev string, partNum int, target string, btrfsSubvols bool) error {
+	opts := ""
+	if btrfsSubvols {
+		opts = BtrfsRootMountOpts
+	}
+	return Mount(PartName(diskDev, partNum), target, opts)
+}
+
 // MountTmpfs mounts a tmpfs of the given size (e.g. "4G") at path, creating
 // the directory if needed.
 func MountTmpfs(path, size string) error {
@@ -138,7 +161,7 @@ func SetupBtrfsSubvolumes(dev, target string) error {
 	}
 
 	// Remount with the @ subvolume and transparent compression.
-	return Mount(dev, target, "subvol=@,compress=zstd:1")
+	return Mount(dev, target, BtrfsRootMountOpts)
 }
 
 // FormatBoot formats a partition as ext4 for use as /boot.

fisherman/internal/disk/format_test.go

@@ -203,6 +203,64 @@ func TestSetupBtrfsSubvolumes(t *testing.T) {
 	}
 }
 
+// ── RemountRoot ───────────────────────────────────────────────────────────
+
+// TestRemountRoot is a regression test for the btrfs-subvolume install that
+// aborted at 99% ("finding composefs deploy etc: reading composefs deploy base
+// …/state/deploy: no such file or directory"). After retagging the root GPT
+// type for systemd-boot GPT auto-discovery, the root partition is remounted;
+// for btrfs subvolume installs it MUST be remounted with subvol=@ so post-install
+// writes reach the @ subvolume where the composefs deployment lives. A bare
+// remount exposes the btrfs top-level, where state/deploy does not exist.
+func TestRemountRoot(t *testing.T) {
+	tests := []struct {
+		name         string
+		btrfsSubvols bool
+		wantOpts     bool // whether -o <opts> should be present
+	}{
+		{name: "btrfs subvolumes preserves subvol=@", btrfsSubvols: true, wantOpts: true},
+		{name: "non-subvolume remounts bare", btrfsSubvols: false, wantOpts: false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			rec := setupRecorder(t)
+			if err := disk.RemountRoot("/dev/nvme0n1", 2, "/mnt/fisherman-target", tt.btrfsSubvols); err != nil {
+				t.Fatalf("RemountRoot: %v", err)
+			}
+			if len(rec.calls) != 1 {
+				t.Fatalf("expected 1 call, got %d: %+v", len(rec.calls), rec.calls)
+			}
+			c := rec.calls[0]
+			if c.name != "mount" {
+				t.Errorf("name = %q, want mount", c.name)
+			}
+			if c.args[len(c.args)-2] != "/dev/nvme0n1p2" {
+				t.Errorf("device arg = %q, want /dev/nvme0n1p2", c.args[len(c.args)-2])
+			}
+			if c.args[len(c.args)-1] != "/mnt/fisherman-target" {
+				t.Errorf("target arg = %q, want /mnt/fisherman-target", c.args[len(c.args)-1])
+			}
+			opts := ""
+			for i, arg := range c.args {
+				if arg == "-o" && i+1 < len(c.args) {
+					opts = c.args[i+1]
+					break
+				}
+			}
+			if tt.wantOpts {
+				if !strings.Contains(opts, "subvol=@") {
+					t.Errorf("btrfs remount opts %q missing subvol=@", opts)
+				}
+				if !strings.Contains(opts, "compress=zstd:1") {
+					t.Errorf("btrfs remount opts %q missing compress=zstd:1", opts)
+				}
+			} else if opts != "" {
+				t.Errorf("non-subvolume remount should have no -o opts, got %q", opts)
+			}
+		})
+	}
+}
+
 // ── BindMount / scratch space ─────────────────────────────────────────────
 
 // TestBindMount verifies that BindMount calls mount --bind with the correct args.