feat(#962): topology-driven child bind mounts + can_manage_top_level_agents role

Removes the MANAGER_NAME special-case from set_nspawn_flags in favour of
two general mechanisms:

1. Topology-driven child mounts: every agent now gets its direct children's
   state, harness, and config dirs bind-mounted (RW). Root's children are
   the top-level agents, so root gets the same access it did before via the
   old /agents blob bind — but derived from topology, not a hardcoded name
   check.

2. can_manage_top_level_agents role: agents holding this role additionally
   get every top-level agent treated as a virtual child (same RW mounts)
   plus /applied and /meta as RO. Designed for recovery: a role holder can
   update a top-level agent's config even when that agent is down.
   Root receives this role by default on first reconcile_roles call.
   Operator can revoke it with set_role.

Every agent (including root) now gets its own state/harness/config dirs via
the standard path. Roles are stored in meta/roles.json (same dir as
topology.json); reconcile_roles is called from reconcile so both files stay
in sync.

hive-c0re/src/lifecycle.rs

@@ -1064,6 +1064,23 @@ const HOST_META_ROOT: &str = "/var/lib/hyperhive/meta";
 /// Shared directory accessible to all agents. All agents bind-mount this RW.
 const HOST_SHARED_ROOT: &str = "/var/lib/hyperhive/shared";
 
+/// Append bind flags for `child`'s state, harness, and config dirs into
+/// `binds`. All three are RW so the parent can read/write state and
+/// submit config-change requests. Creates missing host-side directories
+/// so nspawn doesn't refuse to start; missing dirs are non-fatal.
+fn bind_child_agent_dirs(child: &str, binds: &mut String) {
+    use std::fmt::Write as _;
+    let state_dir = format!("{HOST_AGENTS_ROOT}/{child}/state");
+    let harness_dir = format!("{HOST_AGENTS_ROOT}/{child}/harness");
+    let config_dir = format!("{HOST_AGENTS_ROOT}/{child}/config");
+    for dir in [&state_dir, &harness_dir, &config_dir] {
+        let _ = std::fs::create_dir_all(dir);
+    }
+    let _ = write!(binds, " --bind={state_dir}:/agents/{child}/state");
+    let _ = write!(binds, " --bind={harness_dir}:/agents/{child}/harness");
+    let _ = write!(binds, " --bind={config_dir}:/agents/{child}/config");
+}
+
 fn set_nspawn_flags(
     container: &str,
     runtime_dir: &Path,
@@ -1097,21 +1114,17 @@ fn set_nspawn_flags(
         shared = HOST_SHARED_ROOT,
     );
 
-    // Per-agent state + harness dirs. Skipped for the manager —
+    // Own state, harness, and config dirs — same for every agent including
-    // the `/agents` bind below already exposes both (along with
+    // root. Config is RO: an agent must not edit its own config; changes
-    // every sub-agent's). For regular agents the harness dir is
+    // only ever flow through the approval queue.
-    // the sibling of notes_dir (same parent, "harness" subdir).
+    {
-    if container != MANAGER_CONTAINER {
         let _ = write!(
             binds,
             " --bind={notes}:/agents/{agent_name}/state",
             notes = notes_dir.display(),
         );
-        // Harness dir: sibling of notes_dir under the agent state root.
+        if let Some(state_parent) = notes_dir.parent() {
-        // systemd-nspawn refuses to start when the bind source is missing;
+            let harness_dir = state_parent.join("harness");
-        // ensure_state_dir already creates it, but be defensive here.
-        if let Some(parent) = notes_dir.parent() {
-            let harness_dir = parent.join("harness");
             if !harness_dir.exists() {
                 let _ = std::fs::create_dir_all(&harness_dir);
             }
@@ -1121,34 +1134,41 @@ fn set_nspawn_flags(
                 harness = harness_dir.display(),
             );
         }
+        let own_config = format!("{HOST_AGENTS_ROOT}/{agent_name}/config");
+        std::fs::create_dir_all(&own_config)
+            .with_context(|| format!("create {own_config}"))?;
+        let _ = write!(binds, " --bind-ro={own_config}:/agents/{agent_name}/config");
     }
-    if container == MANAGER_CONTAINER {
+
+    // Topology-driven child mounts: every direct child of this agent gets
+    // its state, harness, and config dirs bind-mounted RW so the parent
+    // can read state and manage config.
+    let direct_children = crate::topology::children_of(agent_name);
+    for child in &direct_children {
+        bind_child_agent_dirs(child, &mut binds);
+    }
+
+    // `can_manage_top_level_agents` role: additionally mount every
+    // top-level agent (direct child of root) as a virtual child. Enables
+    // recovery — a role holder can update a top-level agent's config even
+    // when that agent is down. Also grants RO access to /applied and /meta.
+    if crate::topology::has_role(
+        agent_name,
+        crate::topology::ROLE_CAN_MANAGE_TOP_LEVEL_AGENTS,
+    ) {
+        let top_level = crate::topology::children_of(MANAGER_NAME);
+        for tl in &top_level {
+            if !direct_children.contains(tl) {
+                bind_child_agent_dirs(tl, &mut binds);
+            }
+        }
         // systemd-nspawn refuses to start a container whose bind
         // source doesn't exist. The meta repo is created by the
         // startup migration, but make sure the directory is there
-        // before the manager comes up in case set_nspawn_flags fires
+        // before the role holder comes up in case set_nspawn_flags
-        // first (e.g. cold start with no agents).
+        // fires first (e.g. cold start with no agents).
         std::fs::create_dir_all(HOST_META_ROOT)
             .with_context(|| format!("create {HOST_META_ROOT}"))?;
-        // Manager edits sub-agent proposed/ repos and its own. RW so it can
-        // git-commit. Sub-agents see only their own /run/hive socket and
-        // /root/.claude (no /agents or /applied).
-        //
-        // /applied is a separate RO mount of the hive-c0re-only applied
-        // repos so the manager can `git fetch /applied/<n>/.git
-        // refs/tags/*:refs/tags/applied/*` to mirror deployed/failed/
-        // denied tags into its proposed clones and diff against
-        // what's actually deployed. RO bind makes destructive git
-        // plumbing inside the container unable to corrupt applied.
-        //
-        // /meta is a third RO mount exposing the system-wide deploy
-        // flake (`git log /meta --oneline` shows every deploy across
-        // every agent; `cat /meta/flake.lock` resolves which sha each
-        // agent is pinned at right now).
-        let _ = write!(
-            binds,
-            " --bind={HOST_AGENTS_ROOT}:{CONTAINER_MANAGER_AGENTS_MOUNT}",
-        );
         let _ = write!(
             binds,
             " --bind-ro={HOST_APPLIED_ROOT}:{CONTAINER_MANAGER_APPLIED_MOUNT}",
@@ -1158,24 +1178,6 @@ fn set_nspawn_flags(
             " --bind-ro={HOST_META_ROOT}:{mount}",
             mount = crate::meta::CONTAINER_MANAGER_META_MOUNT,
         );
-    } else {
-        // Sub-agents get a READ-ONLY view of their own proposed
-        // config repo at /agents/<name>/config — agent.nix plus
-        // whatever extra files the manager split the config into.
-        // Lets an agent inspect exactly what defines it and request
-        // precise changes from the manager. RO is load-bearing: the
-        // agent must NOT edit its own config — changes only ever flow
-        // through the manager's RW proposed repo + the approval
-        // queue. The manager already has this dir RW via the /agents
-        // tree bind above.
-        let config_dir = format!("{HOST_AGENTS_ROOT}/{agent_name}/config");
-        // nspawn refuses to start when a bind source is missing.
-        // `setup_proposed` seeds this dir before spawn reaches here,
-        // but create defensively so a missing repo degrades to an
-        // empty RO dir instead of a container that won't boot.
-        std::fs::create_dir_all(&config_dir).with_context(|| format!("create {config_dir}"))?;
-        let _ = write!(binds, " --bind-ro={config_dir}:/agents/{agent_name}/config");
-
     }
     // Web-socket subdir: bind-mount `/run/hive-agent/<name>/` into the
     // container so the harness can bind `web.sock` there and the host-side

hive-c0re/src/topology.rs

@@ -4,6 +4,10 @@
 //! alongside the meta `flake.nix`, so topology changes thread through
 //! the same git commit log as deploys.
 //!
+//! Agent roles are stored alongside in `roles.json` as a flat map of
+//! `name → [role, ...]`. Roles gate additional bind-mount grants; see
+//! `lifecycle::set_nspawn_flags` for the consumer.
+//!
 //! Format, rationale, read/reconcile/inject/surface flow, and target
 //! enforcement semantics: `docs/agent-hierarchy.md::Current state`.
 //! `<parent>` sentinel resolution (delivered by [`resolve_recipient`]):
@@ -278,6 +282,114 @@ pub fn reconcile(agent_names: &[String]) -> std::io::Result<bool> {
     if changed {
         write(&current)?;
     }
+    // Keep roles in sync with the agent set.
+    reconcile_roles(agent_names)?;
+    Ok(changed)
+}
+
+// ---------------------------------------------------------------------------
+// Roles
+// ---------------------------------------------------------------------------
+
+/// Agents with this role have the top-level agents (direct children of the
+/// root/manager agent) added as virtual children for bind-mount and
+/// config-change purposes. Enables recovery: if a top-level agent is down,
+/// a role holder can still read its state and update its config.
+///
+/// The root agent receives this role by default on first `reconcile_roles`
+/// call; operators can revoke it with `set_role`.
+pub const ROLE_CAN_MANAGE_TOP_LEVEL_AGENTS: &str = "can_manage_top_level_agents";
+
+const ROLES_FILE: &str = "roles.json";
+
+#[must_use]
+pub fn roles_path() -> std::path::PathBuf {
+    crate::meta::meta_dir().join(ROLES_FILE)
+}
+
+/// Read the roles map from disk. Returns an empty map when absent or
+/// unparsable — same safe-degradation pattern as `topology::read`.
+#[must_use]
+pub fn read_roles() -> BTreeMap<String, Vec<String>> {
+    let Ok(raw) = std::fs::read_to_string(roles_path()) else {
+        return BTreeMap::new();
+    };
+    serde_json::from_str(&raw).unwrap_or_default()
+}
+
+/// Persist the roles map. Sorted output keeps git diffs minimal.
+pub fn write_roles(roles: &BTreeMap<String, Vec<String>>) -> std::io::Result<()> {
+    let path = roles_path();
+    if let Some(parent) = path.parent() {
+        std::fs::create_dir_all(parent)?;
+    }
+    let text = serde_json::to_string_pretty(roles)
+        .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))?;
+    std::fs::write(&path, format!("{text}\n"))
+}
+
+/// Return true when `name` holds `role`.
+#[must_use]
+pub fn has_role(name: &str, role: &str) -> bool {
+    has_role_in(&read_roles(), name, role)
+}
+
+/// Pure form of [`has_role`] for unit tests.
+#[must_use]
+pub fn has_role_in(roles: &BTreeMap<String, Vec<String>>, name: &str, role: &str) -> bool {
+    roles
+        .get(name)
+        .is_some_and(|rs| rs.iter().any(|r| r == role))
+}
+
+/// Grant or revoke a role for `name`. Idempotent — no disk write when the
+/// state is already correct.
+pub fn set_role(name: &str, role: &str, enabled: bool) -> Result<(), String> {
+    let mut roles = read_roles();
+    let list = roles.entry(name.to_owned()).or_default();
+    let held = list.iter().any(|r| r == role);
+    match (enabled, held) {
+        (true, false) => list.push(role.to_owned()),
+        (false, true) => list.retain(|r| r != role),
+        _ => return Ok(()),
+    }
+    if roles.get(name).is_some_and(|l| l.is_empty()) {
+        roles.remove(name);
+    }
+    write_roles(&roles).map_err(|e| format!("write roles.json: {e}"))
+}
+
+/// Reconcile `roles.json` against the current agent set:
+/// - Seeds root's default `can_manage_top_level_agents` role on first
+///   appearance (operator can revoke with `set_role`).
+/// - Drops entries for agents that no longer exist.
+///
+/// Returns true when the file changed.
+pub fn reconcile_roles(agent_names: &[String]) -> std::io::Result<bool> {
+    let mut roles = read_roles();
+    let mut changed = false;
+
+    let root = crate::lifecycle::MANAGER_NAME;
+    if agent_names.iter().any(|n| n == root) && !roles.contains_key(root) {
+        roles.insert(
+            root.to_owned(),
+            vec![ROLE_CAN_MANAGE_TOP_LEVEL_AGENTS.to_owned()],
+        );
+        changed = true;
+    }
+
+    let known: std::collections::HashSet<_> = agent_names.iter().collect();
+    roles.retain(|name, _| {
+        let keep = known.contains(name);
+        if !keep {
+            changed = true;
+        }
+        keep
+    });
+
+    if changed {
+        write_roles(&roles)?;
+    }
     Ok(changed)
 }