refactor(#2352): subvolume snapshot ops via daemon wire commands

hive-host-sock/src/lib.rs

@@ -188,6 +188,30 @@ pub enum HostRequest {
         #[serde(default)]
         name: Option<String>,
     },
+    /// Migrate an agent's plain state dir to a btrfs subvolume via the
+    /// privileged helper (`hivectl subvol upgrade`). The agent MUST already
+    /// be stopped — the client orchestrates stop → this → start. Returns a
+    /// bare success; the client prints its own progress lines.
+    UpgradeSubvolume { name: String },
+    /// Create a read-only btrfs snapshot of an agent's state subvolume
+    /// (`hivectl subvol snapshot create`). `label` is validated client-side
+    /// AND by hive-priv. Returns the snapshot's host path in
+    /// [`HostResponse::messages`].
+    SnapshotSubvolume { name: String, label: String },
+    /// Delete a snapshot created by `SnapshotSubvolume` (`hivectl subvol
+    /// snapshot delete`). Bare success; the client prints the confirmation.
+    DeleteSnapshot { name: String, label: String },
+    /// Export a snapshot to a local file via `btrfs send` (`hivectl subvol
+    /// snapshot send`). `dest` is a bare filename (hive-priv rejects paths);
+    /// `parent` names an optional parent snapshot for an incremental send.
+    /// Returns the written file's host path in [`HostResponse::messages`].
+    SendSnapshot {
+        name: String,
+        label: String,
+        #[serde(default)]
+        parent: Option<String>,
+        dest: String,
+    },
 }
 
 /// One agent's btrfs qgroup usage row — the [`HostRequest::QuotaShow`]