feat(#1004,#1006): capability system + read_host_journal / get_host_journal MCP tool

hive-sh4re/src/lib.rs

@@ -428,6 +428,25 @@ pub enum Request {
     /// crashed-mid-turn sessions. See
     /// `docs/conventions.md::Broker delivery + ack cycle`.
     RequeueInflight,
+    /// *(capability-gated: `read_host_journal`)* Fetch recent lines
+    /// from the host journal. Filters are all optional; omitting all
+    /// returns the last `lines` entries from the global journal.
+    GetHostJournal {
+        /// Filter to a specific systemd unit (e.g. `hive-c0re.service`).
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        unit: Option<String>,
+        /// Filter to a specific nspawn container by logical agent name
+        /// (e.g. `"iris"` → machine `h-iris`). Adds `-M` flag.
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        container: Option<String>,
+        /// Number of journal lines to return (default 100, max 500).
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        lines: Option<u32>,
+        /// Minimum syslog priority level: `err`, `warning`, `info`, `debug`.
+        /// Corresponds to journalctl `-p LEVEL`.
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        priority: Option<String>,
+    },
 
     // ---- privileged (manager socket only for now) ---------------------------
 
@@ -556,6 +575,10 @@ pub enum Response {
     /// `GetLogs` result: journal lines for the requested container.
     /// Returned on the manager socket only.
     Logs { content: String },
+    /// `GetHostJournal` result: host journal lines matching the
+    /// requested filters. Returned on the agent socket when the agent
+    /// holds the `read_host_journal` capability.
+    HostJournal { content: String },
     /// `ListSchedules` result. Snapshot of every schedule.
     /// Returned on the manager socket only.
     Schedules { schedules: Vec<WireSchedule> },
@@ -821,6 +844,43 @@ impl ToolGroup {
     }
 }
 
+/// Per-agent capability grants. Stored in `meta/capabilities.json`
+/// (same shape as `tool-groups.json`: `{ "alice": ["read_host_journal"] }`).
+/// Capabilities control system-level access that hive-c0re enforces
+/// at dispatch time; they are orthogonal to tool groups (which control
+/// which MCP tools the harness exposes to claude).
+///
+/// Injected into containers as `HIVE_CAPABILITIES` (comma-separated
+/// snake_case) via `meta::render_flake`. The harness reads this to
+/// conditionally register capability-gated MCP tools so claude only
+/// sees tools it can actually invoke. See `docs/conventions.md::Capabilities`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum Capability {
+    /// Agent can lifecycle-manage the root agent (kill/start/restart)
+    /// on behalf of the hive when the root has crashed. Named capability
+    /// for the existing manager privilege — future topology enforcement
+    /// will gate this via the capability system instead of the hardcoded
+    /// `container == MANAGER_CONTAINER` check.
+    ManageRootAgent,
+    /// Agent can read the full host journal via `GetHostJournal`.
+    /// hive-c0re checks this capability before running journalctl.
+    /// MCP tool `get_host_journal` is only registered in the harness
+    /// when this capability is present.
+    ReadHostJournal,
+}
+
+impl Capability {
+    /// Canonical snake_case name for this capability (matches serde).
+    #[must_use]
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::ManageRootAgent => "manage_root_agent",
+            Self::ReadHostJournal => "read_host_journal",
+        }
+    }
+}
+
 /// Schedule row shape on the wire — mirror of
 /// `scheduled_prompts::Schedule` but in the public crate so the
 /// dashboard and agent surfaces can deserialize without depending