remove the get_host_journal MCP tool and its capability

swarm-logs covers every host-tier unit this tool could reach, so the
second, capability-gated path into host journald earns nothing and is
removed outright rather than disabled behind a flag.

Removed end to end: the MCP tool definition + handler, the
GetHostJournal/HostJournal wire variants, hive-c0re's
dispatch_host_journal handler, the ReadHostJournal capability, and the
harness-side capability->--allowedTools gate. get_host_journal was the
only capability that mapped to an MCP tool, so allowed_capability_tools
could only ever return an empty vec; it goes too rather than linger as a
function that provably does nothing.

capabilities::has_cap/caps_for stay: #4624 gave ManageRootAgent's
bind-mount enforcement (hive-c0re/src/lifecycle/host_config.rs) a
second caller of has_cap, so they're no longer callerless once this
lands on top of it.

hive-sh4re's journal module (JournalPriority) had no consumer outside
this tool and is deleted.

An existing capabilities.json still naming read_host_journal does not
error: capabilities::prune_unknown drops unrecognised names with a
warn!, and an agent left with no capabilities has its entry removed. No
migration step is needed.

Untouched: hive-c0re/src/dashboard/journal.rs's
read_host_journal_response, which matches the name but is the private
helper behind the operator-only GET /api/journal-host dashboard route
and carries no capability check.

hive-sh4re/src/journal.rs

@@ -1,41 +0,0 @@
-//! Journal-priority encoding for `GetHostJournal` (`read_host_journal`
-//! capability). One small enum, own topic module rather than a
-//! catch-all — see `hive-sh4re/README.md`'s module list.
-
-use serde::{Deserialize, Serialize};
-
-/// Syslog priority levels for `GetHostJournal`. Serialised as lowercase
-/// strings matching journalctl `-p` accepted values.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize, schemars::JsonSchema)]
-#[serde(rename_all = "lowercase")]
-pub enum JournalPriority {
-    Emerg,
-    Alert,
-    Crit,
-    Err,
-    Warning,
-    Notice,
-    Info,
-    Debug,
-}
-
-impl JournalPriority {
-    /// Returns the lowercase string journalctl expects for `-p`. Named
-    /// `as_journald_str` (not `as_str`) because this is a specific
-    /// external-tool encoding, not the enum's general wire/db string —
-    /// distinct call sites shouldn't reach for this by accident when they
-    /// actually want the serde wire representation.
-    #[must_use]
-    pub fn as_journald_str(self) -> &'static str {
-        match self {
-            Self::Emerg => "emerg",
-            Self::Alert => "alert",
-            Self::Crit => "crit",
-            Self::Err => "err",
-            Self::Warning => "warning",
-            Self::Notice => "notice",
-            Self::Info => "info",
-            Self::Debug => "debug",
-        }
-    }
-}

hive-sh4re/src/lib.rs

@@ -5,7 +5,6 @@ pub mod assets;
 pub mod bash_task;
 pub mod container;
 pub mod inbox;
-pub mod journal;
 pub mod manager;
 pub mod paths;
 pub mod permissions;

hive-sh4re/src/permissions.rs

@@ -354,7 +354,7 @@ impl ToolGroup {
 }
 
 /// Per-agent capability grants. Stored in `meta/capabilities.json`
-/// (same shape as `tool-groups.json`: `{ "alice": ["read_host_journal"] }`).
+/// (same shape as `tool-groups.json`: `{ "alice": ["manage_root_agent"] }`).
 /// Capabilities control system-level access hive-c0re enforces at
 /// dispatch time; they are orthogonal to tool groups (which control
 /// which MCP tools the harness exposes to claude).
@@ -382,17 +382,12 @@ pub enum Capability {
     /// into an unrecognised name that `capabilities::prune_unknown`
     /// silently drops.
     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 {
     /// Every known capability in a stable order. Use this to enumerate
     /// columns in the permissions UI or validate incoming capability strings.
-    pub const ALL: &'static [Self] = &[Self::ManageRootAgent, Self::ReadHostJournal];
+    pub const ALL: &'static [Self] = &[Self::ManageRootAgent];
 
     /// Short human-readable description suitable for a tooltip or help text.
     #[must_use]
@@ -401,7 +396,6 @@ impl Capability {
             Self::ManageRootAgent => {
                 "manage any agent: every agent's state (rw) and config (ro) mounted for recovery"
             }
-            Self::ReadHostJournal => "read host journald via get_host_journal MCP tool",
         }
     }
 }