f817e27d4c
A subagent whose claude process died on a signal — the kernel's OOM
killer, a stopped unit, an `interrupt` — was indistinguishable from one
that finished its turn: its entry left the `running` map, `status` fell
through to "a session exists on disk" and answered `idle`, and the
end-of-turn todo said the subagent had "finished". The usual next move
on that reading is `continue`, which resumes work that was cut mid-turn
with nothing having recorded that it was cut.
The driver already preserves how the child ended — `RunningClaude::wait`
returns `Error::Exit` carrying the `ExitStatus`, whose `signal()` is the
whole answer — so this reads it rather than having to recover it:
`classify_end` turns the outcome into `Complete` / `Killed { signal }` /
`Failed`, and `State::finish_turn` remembers a kill against the name
(cleared by the next confirmed spawn under it).
What an agent sees as a result:
- `status` reports the session killed, naming the signal, instead of idle;
- the todo the daemon pushes without being asked says the subagent was
KILLED mid-turn rather than that it finished;
- `continue` still resumes such a session, but its reply says the
previous turn was killed, so no caller carries on from cut-off work
believing it was complete.
Refs #4326
94 lines
4.5 KiB
Markdown
94 lines
4.5 KiB
Markdown
# Subagent daemon
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`hive-subagent-daemon` (crate `hive-subagent-mcp`) spawns nested headless
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`claude` sessions on request. Own process, own systemd unit, own MCP
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server (`subagent`, not `hyperhive`) — independent of `hive-bash-daemon`:
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a subagent is a full nested claude process, a materially heavier
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capability than a background shell command, so it gets its own
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deployable/restartable unit rather than living inside the bash daemon.
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Shipped default-on for every agent — `nix/agent-modules/mcp.nix` injects
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`subagent` into `hyperhive.extraMcpServers` via `lib.mkDefault`
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(`allowedTools = ["*"]`), same as `bash`. Default-on rather than
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unconditional: an `agent.nix` can override or drop the entry, which is
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what `mkDefault` is there for. The operator's own framing: default-on for
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now, a real opt-in capability later.
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For what the tools do and when an agent should reach for them, see the
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`subagent` MCP server's own tool descriptions and the
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`base:claude-subagents` skill — this page covers the daemon as deployed
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infrastructure, not the agent-facing API.
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## Tools
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Served under the `subagent` MCP server (`mcp__subagent__<tool>`): `start`,
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`continue`, `status`, `interrupt`.
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## State
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In-memory only: a map of currently running processes, live only as long
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as the daemon process is. A daemon restart stops whatever was running
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rather than adopting it. The durable record of a subagent's existence is
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claude's own on-disk session (`hive_claude::SessionStore`), which
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`continue` reattaches to independent of the daemon's own lifetime — a
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restart loses the _in-flight turn_, not the subagent's history.
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## A killed turn
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A subagent whose `claude` process dies on a signal — the kernel's OOM
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killer under memory pressure, a stopped unit, an `interrupt` from the
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owning agent — did not finish its turn, and the daemon says so rather
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than letting it settle back into `idle`:
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- `status` reports the session **killed**, naming the signal, instead of
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the `idle` it reports for a turn that ended on its own;
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- the end-of-turn todo the daemon pushes without being asked says the
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subagent was killed mid-turn, not that it finished;
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- `continue` still resumes such a session — often what you want — but
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its reply says the previous turn was killed, so nobody carries on from
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cut-off work believing it was complete.
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The record is per-name, in memory with the rest of this daemon's state,
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and the next confirmed spawn under that name clears it. A daemon restart
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loses it along with everything else — the daemon has to outlive the kill
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to report it, which is what `OOMPolicy=continue` on the unit is for.
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## Compaction trade-off
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Built on `hive_claude::Claude::spawn` + `RunningClaude::wait` directly
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rather than `InfiniteSession::run`, since only the low-level driver
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exposes a cancel handle to stop a turn mid-flight — that's what makes
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`interrupt` genuinely stop a running turn rather than only cancelling a
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still-pending one. The cost: a turn that overflows the context window
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surfaces as an error rather than self-healing via reactive compaction.
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Subagents are meant to be bounded, single-batch work, not sessions
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long-lived enough to need in-place compaction — a real follow-up if that
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assumption stops holding.
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## Configuration
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`hyperhive.mcp.subagentHttpPort` — the daemon's streamable-http listen
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port. Same pattern as `bashHttpPort`/`matrixHttpPort`: a per-agent default
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assigned by `nix/agent-modules/mcp.nix`, only worth overriding for an
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agent that needs a stable or non-default port.
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Own systemd unit, defined alongside the other per-agent MCP daemons in
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`nix/agent-modules/mcp.nix`.
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## MCP servers available to a subagent
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A subagent runs with `--strict-mcp-config` and no `--mcp-config` by
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default — zero MCP servers, full stop; it falls back to claude's own
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native tools (`Bash`, `WebFetch`, etc.), not the parent's `mcp__bash__*` /
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`mcp__hyperhive__*` surface. Nothing implicit reaches it: the built-in
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hyperhive surface (todos/messaging) isn't an `extraMcpServers` entry at
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all, and the automatically injected `bash`/`subagent` entries default to excluded
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too (a subagent can't spawn hive-bash tasks or its own nested subagents
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unless an operator opts them in explicitly, same as anything else).
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Set `hyperhive.extraMcpServers.<name>.availableToSubagents = true` on a
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specific entry to hand that one server to subagents as well — useful for,
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say, a read-only lookup or scraper MCP a subagent's bounded, single-batch
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task might need. `hive-subagent-mcp`'s `mcp_config` module renders the
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opted-in subset into its own `--mcp-config` file per turn; an entry left
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at the default `false` never appears there.
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