refactor(#2352): quota show via daemon wire command

hive-host-sock/src/lib.rs

@@ -178,6 +178,35 @@ pub enum HostRequest {
         #[serde(default)]
         limit: Option<u64>,
     },
+    /// Report per-agent btrfs qgroup usage (`hivectl quota show [name]`).
+    /// The daemon resolves the agent set (all kept state dirs when `name`
+    /// is absent) and reads each subvolume's referenced/exclusive usage via
+    /// the privileged helper. Result rows land in [`HostResponse::quota`];
+    /// a "btrfs quota not enabled" error short-circuits the whole sweep as a
+    /// plain [`HostResponse::error`] so the client can print the enable hint.
+    QuotaShow {
+        #[serde(default)]
+        name: Option<String>,
+    },
+}
+
+/// One agent's btrfs qgroup usage row — the [`HostRequest::QuotaShow`]
+/// result unit. `referenced` / `exclusive` are byte counts when the agent
+/// has a live qgroup; both are `None` (with an explanatory `note`) for a
+/// plain-dir agent that has no subvolume to account. The client formats the
+/// byte counts into human-readable columns.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct QuotaRow {
+    pub agent: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub referenced: Option<u64>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub exclusive: Option<u64>,
+    /// Set instead of the byte counts when the agent has no qgroup data
+    /// (plain dir, or a non-"quota not enabled" read error), so the client
+    /// can print an inline explanation and keep going.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub note: Option<String>,
 }
 
 /// Selects which container classes a hive-wide [`HostRequest::Stop`] /
@@ -280,6 +309,10 @@ pub struct HostResponse {
     /// Empty for requests that produce no such output.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub messages: Vec<String>,
+    /// `QuotaShow` result — one row per agent with its btrfs qgroup usage.
+    /// `None` for every other request kind.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub quota: Option<Vec<QuotaRow>>,
 }
 
 impl HostResponse {
@@ -369,4 +402,14 @@ impl HostResponse {
             ..Self::default()
         }
     }
+
+    /// `QuotaShow` result — one usage row per agent.
+    #[must_use]
+    pub fn quota(rows: Vec<QuotaRow>) -> Self {
+        Self {
+            ok: true,
+            quota: Some(rows),
+            ..Self::default()
+        }
+    }
 }