agent permissions: one set, tool groups included, set at agent creation

mara on #5170: "dont split caps and perms. its all perms. / dont include
the now empty tool groups / nothing set -> default / also add perms to
agent creation screen".

- hive-sh4re: one `Permission` enum (messaging, meta, inbox, execution,
  web_tools, manage_root_agent) replaces `ToolGroup` and `Capability`;
  `lifecycle`/`forge` are gone. `Permission::default_for` is the default
  for an agent the swarm sets nothing for.
- The record is `{ "permissions": [...] }`. Missing key, unset field or
  no successful read yet = default; `[]` = none; a failed read after a
  good one keeps the last value.
- hive-agent reads its own key every 10s and builds each turn's --tools,
  --allowedTools and MCP config (rewritten before every turn) from it;
  the subagent daemon reads it on each start/continue. Agents get a
  read-only grant on their own key.
- hive-c0re restarts an agent only when its manage_root_agent changes.
  The import now merges meta/capabilities.json and meta/tool-groups.json
  into one list per agent and deletes both; the "import pending, don't
  read" decision is `ImportOutcome::read_allowed`, table-tested.
- swarm-controller: `GET /api/permissions` (names + default) and an
  optional `permissions` on `POST /api/agents`, stored before the job is
  queued. swarm-ui's create-agent form gets a permissions field.
- Deleted: HIVE_TOOL_GROUPS and its forward to the subagent daemon,
  tool_groups.rs, ruth's tool-group seed, the permissions rebuild job
  (PermPayload/WritePermFile/perm_change), the dashboard permissions tab
  and its stale-entries panel.

Part of #5170.

hive-c0re/src/agent_config/permissions.rs

@@ -0,0 +1,97 @@
+//! The permissions the swarm grants this hive's agents, as last read from the
+//! `agent-permissions` bucket by `workers::swarm_permissions`. Stored at
+//! `/var/lib/hyperhive/swarm-agent-permissions.json`, outside the meta repo:
+//! the swarm is the record, this file is the hive's last read of it.
+//!
+//! Format: agent name → the stored
+//! [`swarm_queue_client::agent_permissions::AgentPermissions`]. An agent with
+//! no entry, or an entry with `permissions` unset, holds
+//! [`Permission::default_for`]; `"permissions": []` holds none.
+//!
+//! hive-c0re enforces one member, [`Permission::ManageRootAgent`]: read by
+//! `lifecycle::host_config::set_nspawn_flags` on every container start, which
+//! is why a change to it takes a restart. The agent reads the tool members
+//! itself.
+
+use std::collections::BTreeMap;
+use std::path::{Path, PathBuf};
+
+use hive_sh4re::permissions::Permission;
+use swarm_queue_client::agent_permissions::AgentPermissions;
+
+const FILE: &str = "swarm-agent-permissions.json";
+
+pub type Stored = BTreeMap<String, AgentPermissions>;
+
+#[must_use]
+pub fn path() -> PathBuf {
+    crate::paths::state_root().join(FILE)
+}
+
+/// Read the stored permissions. An absent file is the empty map: every agent
+/// on its default. A file that exists but can't be read or parsed is an error.
+pub fn read_at(path: &Path) -> std::io::Result<Stored> {
+    super::read_map(path)
+}
+
+/// Persist the permissions atomically.
+pub fn write_at(path: &Path, stored: &Stored) -> std::io::Result<()> {
+    super::write_map(path, stored)
+}
+
+/// The permissions `agent` holds under `record`.
+#[must_use]
+pub fn effective(agent: &str, record: Option<&AgentPermissions>) -> Vec<Permission> {
+    record
+        .and_then(|r| r.permissions.clone())
+        .unwrap_or_else(|| Permission::default_for(agent))
+}
+
+/// Whether `agent` holds `perm` per the file at `path` (normally [`path`]).
+///
+/// # Errors
+///
+/// As [`read_at`].
+pub fn holds(path: &Path, agent: &str, perm: Permission) -> std::io::Result<bool> {
+    Ok(effective(agent, read_at(path)?.get(agent)).contains(&perm))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn record(json: &str) -> AgentPermissions {
+        serde_json::from_str(json).expect("decodes")
+    }
+
+    #[test]
+    fn unset_is_the_default_and_an_empty_list_is_none() {
+        assert!(effective("ruth", None).contains(&Permission::ManageRootAgent));
+        assert!(effective("ruth", Some(&record("{}"))).contains(&Permission::ManageRootAgent));
+        assert!(effective("ruth", Some(&record(r#"{"permissions":[]}"#))).is_empty());
+        assert_eq!(effective("atlas", None), Permission::DEFAULT.to_vec());
+        assert_eq!(
+            effective(
+                "atlas",
+                Some(&record(r#"{"permissions":["manage_root_agent"]}"#))
+            ),
+            vec![Permission::ManageRootAgent]
+        );
+    }
+
+    #[test]
+    fn a_missing_file_holds_the_defaults() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let path = dir.path().join(FILE);
+        assert!(holds(&path, "ruth", Permission::ManageRootAgent).expect("missing is empty"));
+        assert!(!holds(&path, "atlas", Permission::ManageRootAgent).expect("missing is empty"));
+    }
+
+    #[test]
+    fn a_corrupt_file_is_an_error() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let path = dir.path().join(FILE);
+        std::fs::write(&path, "{\n  \"ruth\": {\"permissions\": [\"manage_root_ag").expect("seed");
+        holds(&path, "ruth", Permission::ManageRootAgent).expect_err("truncated JSON");
+    }
+}