hyperhive/docs/agent-lifecycle/agent-hierarchy.md

Agent roster & privileges

Agents are a flat set, with no parent/child tree: the parent field topology.json used to carry is gone, along with every mechanism that read it. The capability store scopes which agents can manage which others; a tree position no longer scopes anything.

This doc covers what the roster file is now, what the removal took with it, and where the manager still gets special-cased, as a tracked cleanup.

Where the roster lives

The roster lives in the hive-c0re-owned meta repo, alongside flake.nix, at /var/lib/hyperhive/meta/topology.json:

["alice", "bob", "ruth"]

One entry per agent the hive knows about, in name order. The file carries no per-agent value any more, and encodes no ordering or grouping — it answers exactly one question, which agents exist, and topology::all_agents is the only reader that matters.

That reader is a permission boundary: the set it returns is what an agent holding the ManageRootAgent capability gets bind-mounted (each other agent's state read-write and config read-only; never harness). An agent holding no capability sees its own dirs and nothing else. See persistence.md's Cross-agent access to state.

Reading the legacy format

topology.json used to be a map of name → parent | null. The reader still accepts that shape and keeps its keys, so a hive upgrading across the change reads the same roster rather than an empty one. An empty roster costs more than a cosmetic gap: every capability holder loses its mounts until the next reconcile pass writes the array form.

Why meta, not per-agent agent.nix

An agent shouldn't be able to add itself to a set that governs who may reach its state dir. The roster IS a system-level fact; meta is where system-level facts live.

How topology.json gets updated

• Read — parsed into a set of names; a missing or unparsable file degrades safely to "no agents" (covers a fresh install that hasn't synced yet).
• Reconcile — runs alongside the periodic meta/flake regeneration. Adds newly-spawned agents, drops removed ones. Reconcile keeps agents whose config repo exists but that haven't spawned yet, so the gap until the container appears doesn't churn the file.

No write API and no operator verb reach this file. Reconcile derives it from which agents exist, so the next pass overwrites a hand edit.

See hive-c0re/src/agent_config/topology.rs and hive-c0re/src/meta.rs's module docs for the exact call chain.

What the parent field used to do

Recorded so a reader who finds one of these in an old branch, an issue thread or a stale comment knows each one went away rather than moved:

gone	what replaced it
<parent> recipient sentinel	address operator directly
<children> fan-out recipient	nothing — name the recipients, or broadcast to *
hivectl agent <name> set-parent	nothing
POST /api/topology/set-parent{,-bulk}	nothing
HostRequest::SetParent	nothing
NodeKind::Reparent and its DAG template	nothing
HIVE_PARENT on the container	nothing — no consumer ever read it
every agent's grant over its direct children	the ManageRootAgent capability, for every agent
rebuild ordering by topology depth	alphabetical, which the depth sort already produced

The last row is the one with teeth: an agent that used to reach a child's state dir by virtue of being its parent no longer reaches it at all unless it holds ManageRootAgent. That narrowing is the intended consequence of removing the field, not a side effect of it.

Manager special-casing today

Capability enforcement isn't fully wired yet, so the manager (ruth) still gets some hard-coded special treatment other agents don't:

• Naming/bootstrap — the manager's broker recipient name, state-dir key, and nixos-container name are all ruth (container h-ruth). hive-c0re spawns it directly at boot if missing, with no operator approval step — every other agent goes through a Spawn approval. Roster-wise, ruth is just another entry.
• Wire-protocol — the privileged Request variants (Kill / Start / Restart / Update; GetLogs) — marked *(privileged)* in hive-core-agent-sock's unified Request enum — are reachable only from the manager's socket flavour today; each is planned to become a capability check. One exception: Wake (inject a from: <X> message into the caller's own inbox) isn't really privileged — every per-agent daemon (for example hive-forge-notify) needs it, and sub-agents already have the equivalent on their own socket.
• Storage/mounts — only the manager container gets /var/lib/hyperhive/agents bind-mounted RW at /agents (so it can manage any agent's state dir — config isn't authored there, since a real config change is a PR from a clone), plus RO mounts for /applied (diff against what's deployed) and /meta (system-wide deploy log). That grant is the ManageRootAgent capability now, and ruth holds it; no name check remains. hive-c0re will gate RO /meta access on a "meta read" capability; no agent-facing path writes flake.lock any more — request_update_meta_inputs was removed, leaving the operator dashboard's POST /api/meta-update as the only entry point.
• Prompt/tools — the system prompt uses <!-- role:agent --> / <!-- role:manager --> marker blocks, and a Flavor::{Agent, Manager} switch picks the MCP tool allow-list claude sees. Both are already parametrised on a single flavour value, so the planned per-capability-group version (cap:<group> prompt blocks + a matching tool allow-list) is additive rather than a rewrite.
• State dirs — not special-cased: HYPERHIVE_STATE_DIR is injected uniformly via systemd.globalEnvironment for every container including the manager, so all token/state paths resolve through it the same way everywhere.
• Scattered ownership checks — a handful of independent manager-only overrides exist across hive-c0re today: loose-ends visibility (manager sees hive-wide, sub-agents only their own), destroy refusing to act on the manager, and crash-watch skipping the manager (it autorestarts via systemd instead of going through the crash-watch loop). Each is planned to become a capability check instead of a manager-name check — see the module docs for loose_ends.rs, stores/broker.rs, actions.rs, and workers/crash_watch.rs for the current owner-check logic in each. (The harness handles reminder cancellation fully in-agent — see the note on CancelLooseEndKind::Reminder in hive-c0re/src/socket_server/mod.rs.)

None of the above is a stable interface — treat the module doc comments as the source of truth for exactly which checks exist today.

Harness systemd unit shape

One harness serve binary (hive-agent, with its hive-agent-mcp sibling), one shared nix/agent-modules/ tree, one service unit (systemd.services.hive-agent) for all agents. No separate manager service name or role distinction exists in the harness — privilege differences live server-side in the broker socket (which tool groups and manager-surface calls each agent receives).

agent.nix and ruth.nix both import the shared nix/agent-modules/. ruth.nix additionally sets forge defaults to suppress the subscription/participation firehose so ruth's inbox stays focused on direct mentions, reviews, and assignments.

Environment variables set on the unit

• HOME = /home/<userName> — systemd defaults HOME to / for services without User= set; with the per-agent user the harness needs the right home so claude finds its bind-mounted ~/.claude/ session dir.
• HIVE_STATIC_DIR = <mergedDist> — tower_http::ServeDir root for the per-agent web UI; merged dist = agent default + every services.hyperhive.agent.frontend.extraFiles overlay.
• HIVE_ASSETS_DIR = pkgs.hyperhive-assets/share/hyperhive — set directly on the unit, not via environment.variables, because the latter only populates /etc/profile which systemd services don't inherit.

PATH setup (the wrapper-dir trick)

path = [ "/run/wrappers" "/run/current-system/sw" ];

/run/wrappers (not /run/wrappers/bin) comes first so setuid wrappers — notably sudo — resolve before bare nix-store binaries; see docs/process/gotchas.md ("systemd.services.*.path appends /bin to every entry") for why the trailing /bin matters in general. It's load-bearing here because the harness runs as the per-agent user: without the wrapper dir on PATH, sudo resolves to the non-setuid nix-store binary and every services.hyperhive.agent.user.passwordlessSudo grant fails with "must be owned by uid 0 and have the setuid bit set."

serviceConfig highlights

• ExecStart = pkgs.hyperhive/bin/hive-agent — same binary for every agent.
• Restart = on-failure, RestartSec = 2 — keeps the harness resilient across transient crashes without thundering retries.
• RuntimeDirectory = "hive-config" → /run/hive-config/ owned by User=, autocleared on stop. The harness writes regenerated claude-{mcp-config,settings,system-prompt} files there (paths::config_dir). Deliberately separate from /run/hive, which the host bind-mounts in root-owned and which holds hive-c0re's mcp.sock.
• User = Group = userName — drops root inside the container; sudo is the explicit escalation surface (services.hyperhive.agent.user.passwordlessSudo).

Cross-references

• Milestone: "Agent privileges and sub-agents" (tracked internally)
• Audit table source: milestone comment (tracked internally)
• Operator/agent trust boundary (orthogonal axis): boundary.md