# Turn loop + MCP

How the harness wakes up, what it asks claude to do, and what tools
claude has access to in return.

## The loop

Each agent harness (`hive-ag3nt serve` or `hive-m1nd serve`) runs:

1. Long-poll `Recv` on its socket. The host-side broker
   (`broker.rs::recv_blocking`) returns immediately if there's a
   pending message, otherwise waits up to 30 s for a broker `Sent`
   event for this recipient.
2. Pop one message. Peek the remaining inbox depth with `Status`.
3. Emit `LiveEvent::TurnStart { from, body, unread }` onto the SSE
   bus.
4. Spawn claude (one process per turn) and pipe the wake prompt
   over stdin.
5. Stream stdout (JSON lines) into the bus as
   `LiveEvent::Stream(value)`. Pump stderr as `Note`.
6. Wait for claude to exit. On `Prompt is too long`, run `/compact`
   on the session once and retry the turn.
7. Emit `LiveEvent::TurnEnd { ok, note }`. Sleep `poll_ms` to avoid
   tight loops on transient failures.

## The claude invocation

```
claude --print --verbose --output-format stream-json --model <name> \
  --continue --settings /run/hive/claude-settings.json \
  --system-prompt-file /run/hive/claude-system-prompt.md \
  --mcp-config /run/hive/claude-mcp-config.json --strict-mcp-config \
  --tools <builtins> --allowedTools <builtins+mcp>
# wake prompt piped over stdin
```

`<name>` is read from `Bus::model()` on each turn, default
`haiku`. Operator can flip it at runtime with `/model <name>` in
the web terminal — the next turn picks it up.  The choice is
persisted to `/state/hyperhive-model` so it survives restart;
override path: `HYPERHIVE_MODEL_FILE` env var for tests.

`--continue` keeps a persistent session per agent (claude stores
sessions in `~/.claude/projects/`, which is bind-mounted
persistently). Auto-compact and auto-memory are disabled via
`--settings` because hyperhive owns compaction (`/compact` on
overflow, retry once; operator can also force one via `/api/compact`).
A one-shot `--continue` suppression is available via
`POST /api/new-session` (or `/new-session` slash command in the
per-agent terminal) — `Bus::take_skip_continue()` flips an
`AtomicBool` once per turn, the next claude invocation drops
`--continue`, every subsequent turn resumes normal behaviour.

The child runs with `cwd = /state` (when the bind exists; falls
back to the parent's cwd in dev), so any relative path in a tool
call (`Read foo.md`, `Bash ls`, `Write notes.md`) lands in the
agent's durable bind-mounted dir. CLAUDE.md auto-load walks
upward from `/state` — drop a per-agent CLAUDE.md there if you
want long-term hints that survive destroy/recreate.

The wake prompt is intentionally minimal: just the popped message's
`from`/`body`, plus an inline `({unread} more pending — drain via
…)` hint when `unread > 0`. Claude drives any further `recv`/`send`
itself via the embedded MCP server.

Whenever hive-c0re starts / restarts / rebuilds a container, it
also drops a `system` message into the agent's inbox via
`Coordinator::kick_agent` — a one-line "you were just (re)started,
check /state/ for your notes, --continue session is intact". The
next turn picks it up like any other inbox message.

### On-boot files

`hive_ag3nt::turn::write_*` writes three files next to the per-agent
socket at `/run/hive/` once at startup:

- `claude-mcp-config.json` — re-invokes the running binary as `mcp`
  child (so the same binary serves as harness + as claude's MCP
  child process).
- `claude-settings.json` — the `--settings` blob (auto-compact and
  auto-memory off, effortLevel medium).
- `claude-system-prompt.md` — rendered from
  `hive-ag3nt/prompts/{agent,manager}.md` with `{label}` and
  `{operator_pronouns}` substituted. Pronouns come from
  `HIVE_OPERATOR_PRONOUNS` env (set by the meta flake from
  `services.hive-c0re.operatorPronouns`, default `she/her`).
  Passed via `--system-prompt-file`.

The shared per-turn plumbing lives in `hive_ag3nt::turn::{write_mcp_config,
write_settings, write_system_prompt, run_turn, drive_turn,
emit_turn_end, wait_for_login, compact_session}` so the two binaries
can't drift.

## MCP surface

The harness ships an embedded MCP server (rmcp 1.7). Claude launches
it as a stdio child via `--mcp-config`. The hyperhive socket name is
`hyperhive`, so the tools land in claude as `mcp__hyperhive__<tool>`.

### Sub-agent tools

- `send(to, body)` — message a peer (logical agent name), another
  agent, or the operator (recipient `operator`, surfaces in the
  dashboard inbox).
- `recv(wait_seconds?)` — drain one inbox message. Long-polls
  server-side; `wait_seconds` is capped at 180 (default 30 when
  omitted). Agents use a long wait to park their turn waiting for
  work instead of busy-looping with short polls — they wake
  instantly when a message arrives.
- `ask_operator(question, options?, multi?, ttl_seconds?)` —
  surface a question on the dashboard. Same shape as the manager's;
  answer routes back to the asker's own inbox as
  `HelperEvent::OperatorAnswered` via `coord.notify_agent`.

### Extra MCP servers (per-agent)

Each agent's NixOS config can declare additional MCP servers via
`hyperhive.extraMcpServers.<key> = { command, args, env,
allowedTools }`. The module writes the map to
`/etc/hyperhive/extra-mcp.json`; the harness reads it at boot and
merges every entry into `--mcp-config` (under `mcpServers.<key>`)
and `--allowedTools` (as `mcp__<key>__<pattern>`). The agent's
flake.nix forwards every flake input to `agent.nix` as the
`flakeInputs` module arg, so external MCP-server flakes are pulled
in by adding them to `inputs.*` and referenced as
`flakeInputs.<name>.packages.${pkgs.system}.default` — the
resolved sha lands in the agent's own `flake.lock` and rolls up to
meta's.

### Manager tools (in addition to send/recv)

- `request_spawn(name)` — queue a Spawn approval for a brand-new
  sub-agent (≤9 char name). Operator approves on the dashboard.
- `kill(name)` — graceful stop. No approval required.
- `start(name)` — start a stopped sub-agent. No approval.
- `restart(name)` — stop + start. No approval.
- `update(name)` — rebuild (re-applies the current hyperhive flake
  + agent.nix, restarts). No approval, idempotent. Manager calls
  this on receipt of a `needs_update` system event.
- `request_apply_commit(agent, commit_ref)` — submit a config
  change for any agent (`hm1nd` for the manager's own config) for
  operator approval.
- `ask_operator(question, options?, multi?, ttl_seconds?)` —
  surface a question on the dashboard. Non-blocking — returns the
  queued question id; the operator's answer arrives later as
  `HelperEvent::OperatorAnswered` in the manager inbox. Options
  always render alongside a free-text fallback; `multi=true`
  renders options as checkboxes. `ttl_seconds` auto-cancels with
  answer `[expired]` after the deadline (useful for time-sensitive
  decisions that become moot if the operator hasn't responded).
  The operator can also manually cancel with `[cancelled]` via the
  dashboard.

The boundary: lifecycle ops on *existing* sub-agents
(`kill`/`start`/`restart`) are at the manager's discretion — no
operator approval. Creating a new agent (`request_spawn`) and
changing any agent's config (`request_apply_commit`) still go
through the approval queue.

### Authoritative state

`hive_ag3nt::events::Bus` carries the current turn-loop state in
addition to the broadcast channel and the events history. Variants:

- `Idle` — sitting on `Recv` waiting for mail.
- `Thinking` — `claude --print` is running for a turn.
- `Compacting` — operator-triggered `/compact` is in flight.

The harness flips state at the relevant transitions
(`set_state(Thinking)` before `drive_turn`, `set_state(Idle)`
after; `set_state(Compacting)` around `compact_session`). Exposed
via `/api/state.turn_state` + `turn_state_since` (unix seconds);
the agent page renders this rather than deriving from SSE events.

### Tool envelope

`mcp::run_tool_envelope`: every MCP tool handler logs the request,
runs the body, logs the result. Pre-/post-log only — the inbox
status hint moved to the wake prompt + UI header.

### Tool whitelist (`mcp::ALLOWED_BUILTIN_TOOLS`)

- Allowed built-ins: `Bash`, `Edit`, `Glob`, `Grep`, `Read`,
  `TodoWrite`, `Write`.
- Denied by omission: `WebFetch`, `WebSearch`, `Task`,
  `NotebookEdit`.
- Allowed MCP tools: as listed above per flavor.

`Bash` is on the allow-list pending a finer-grained pattern allow-list
(`Bash(git *)`-style) — see [TODO](../TODO.md).