The claude invocation

claude --print --verbose --output-format stream-json --model <name> \
  --effort <level> --resume <title>   # or --name <title> on first use \
  --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

Crate split. The generic subprocess mechanics — spawning claude --print, streaming + classifying stream-json, session lookup/archive, and the durable-session compaction loop — live in the reusable hive-claude crate (hive_claude::{Claude, InfiniteSession, Attach, CompactionPolicy, PercentPolicy, Telemetry, Sink, SessionStore}; see hive-claude/README.md). hive-agent's turn module is the hyperhive policy layer on top: it builds the per-turn config from the bus, bridges the output stream onto the event bus (BusSink), and owns the compaction / autoreset / retry decisions in drive_turn. The lib returns everything it parsed from a turn (usage, cost, context window, resolved model) as Telemetry, which the policy layer applies to the bus.

Which claude binary. The bare name claude, resolved off the harness unit's PATH. By default that's the claude-code in the agent's own nixpkgs (the meta flake's nixpkgs input) via environment.systemPackages. Since that's typically a release channel and this package moves fast, the operator can pin one hive-wide with services.hyperhive.c0re.claudeCodePackage: its store path is written into each agent's flake, and claude on PATH becomes a symlink to it instead of the container's own claude-code — so there's only ever one claude in the container. Agents pick up a new build on their next rebuild, not live. See docs/process/gotchas.md::claude-code is unfree.

Hive-enforced settings ship at /etc/claude-code/managed-settings.json (claude-code's canonical managed-settings path — precedence #1, read-only, un-overridable), wired in nix/agent-modules/claude-settings.nix from the prompts/claude-settings.json asset. effortLevel is deliberately not in that file — effort is controlled live via the --effort flag (HIVE_DEFAULT_EFFORT / the per-agent UI slider), which managed scope would otherwise lock.

<name> is read from Bus::model() on each turn. The initial default is set by hyperhive.model in the agent's agent.nix (NixOS option; propagates via HIVE_DEFAULT_MODEL env var; falls back to "haiku" if unset). The operator can flip it at runtime with /model <name> in the web terminal — the next turn picks it up. The choice is persisted to /harness/hyperhive-model so it survives restart; override path: HYPERHIVE_MODEL_FILE env var for tests.

Context-window size is looked up per-model via harness_state::context_window_tokens(model). Resolution order (first match wins):

1. HIVE_CONTEXT_WINDOW_TOKENS_<KEY> env var, where KEY (lowercased) is a substring of the active model name. Injected by the meta flake from services.hyperhive.c0re.contextWindowTokens (host-level NixOS option, defaults: haiku=200k, sonnet=1M, opus=1M). Override these for all agents at once without a per-agent config change.
2. HIVE_CONTEXT_WINDOW_TOKENS — single global override for any model (useful in dev / test).
3. Hard fallback: 200_000 (conservative; only reached outside NixOS where the env vars aren't set).

The effective window drives watermarks and is exposed at runtime via /api/state.context_window_tokens so the UI can show a percentage-of-window ctx badge.

Session identity — a constant title. Every turn keys on one fixed, harness-owned session title (turn::session_title(), default hive-session, override HIVE_SESSION_TITLE). The durable hive_claude::InfiniteSession (built once by the serve loop via turn::make_session, then reused) --resume <title>s it; the first use (bootstrap, post-archive, post-purge) misses and the session re-runs the same prompt once with --name <title> to mint it. That single self-heal rule is the whole identity system — there is no scraped session-id file. Because the title is constant, /compact and its post-compact retry provably target the same session (killing the old "compact ran on a different/empty session" bug), and a choom invocation in the same cwd can't hijack the context (it won't carry our title). claude stores sessions in ~/.claude/projects/<cwd-slug>/<uuid>.jsonl (bind-mounted persistently); --name writes the title into the file as a custom-title event, which is what --resume <title> resolves against. We never pass bare --continue (it resumes the latest session in the cwd — the hijack vector). Automemory and dynamic workflows (the /workflows feature) are disabled via the managed settings at /etc/claude-code/managed-settings.json: disableWorkflows keeps the /workflows machinery from spawning sub-runs that burn usage on the harness's autonomous turns. Claude's own native autocompact is on, at the widest window claude-code allows — see Compaction below for why (it's a safety net, not the primary mechanism; hyperhive still owns that).

Session reset is available via POST /api/new-session (or /new-session slash command). It does not touch the session inline — that would race a mid-write claude process. Instead Bus::request_session_reset() sets a one-shot flag consumed at the next turn boundary by drive_turn, which archives the current session: the backing <uuid>.jsonl is renamed to <uuid>.jsonl.archived (dropped out of claude's *.jsonl resolution glob, history preserved on disk, only the file carrying our title — any choom session sharing the cwd is left alone). The next turn's --resume <title> then misses and self-heals into a fresh session.

Compaction

hyperhive owns compaction as policy: the hive_claude::InfiniteSession keeps the session alive across the context window with two triggers baked into its run:

• Reactive — claude-code prints Prompt is too long. The session is already past the window, so no turn can run on it — the session /compacts straight away and retries the same wake-up prompt once. No notes-checkpoint turn is possible here: the detail is gone. If the retry still overflows, run surfaces Error::PromptTooLong; drive_turn then archives the session (session lifecycle stays hive-side) and the serve loop requeues the message so it redelivers into a fresh session (see Turn outcomes — the wake prompt itself is small, so the overflow was the accumulated context the archive clears).
• Proactive — a turn finishes cleanly but the last inference's context size crossed the policy watermark. While the session is still healthy it runs one synthetic notes-checkpoint turn (CHECKPOINT_PROMPT — "context is filling up, flush durable state into /state now") and then /compacts, so the agent can persist in-flight state before the detail collapses into a summary.

Both triggers above are checked between hive-agent's own turns — the percent watermark is read from the last completed turn's telemetry (PercentPolicy::should_compact, checked after attempt() returns), and the reactive path only fires once claude-code has already refused a whole turn as too long. Neither can see context growth happening inside a single long turn's own tool-calling before it returns — a turn whose tool calls alone blow past the window hits the reactive path with no preceding checkpoint, losing whatever wasn't already persisted (#2707, root-caused in #3727).

Safety net for that gap: claude-code's own native autocompact is on, via the managed settings ("autoCompactEnabled": true, "autoCompactWindow": 1000000 — the CLI's documented max, so it fires only right before the real hard limit, not as an earlier watermark). This is deliberately not the primary mechanism — it runs with no checkpoint and none of the CHECKPOINT_PROMPT notes-flush machinery above, so a session saved by it still loses whatever wasn't already durable — but it can act mid-turn, underneath InfiniteSession::run, which the two triggers above structurally can't. Don't confuse this with the hyperhive.autoCompact nix option below: that one is a per-agent on/off for hyperhive's own proactive watermark and has no effect on claude's native mechanism, which is fleet-wide and set once in hive-agent/prompts/claude-settings.json.

The when for hyperhive's own policy is a hive_claude::CompactionPolicy injected by the harness: turn::make_session builds a PercentPolicy that compacts once the model-reported context fill reaches HIVE_COMPACT_WATERMARK_PERCENT (default 75%), falling back to harness_state::context_window_tokens(model) for the window on turns the model didn't report one. 0 disables proactive compaction (the reactive path always applies). The proactive path is best-effort — a failed checkpoint or /compact never fails the turn that already succeeded.

The operator can force a compaction any time via POST /api/compact. It's deferred: the handler sets Bus::request_compact() and returns immediately; the harness runs the /compact at the next turn boundary (end of the in-flight turn in drive_turn, or — when the agent is idle — in turn::run_pending_compact on the serve loop's next empty poll). This lets /api/compact work mid-turn instead of only when idle, without racing a live claude process.

To disable proactive compaction for a specific agent, use the nix option:

hyperhive.autoCompact = false;  # default true

Setting autoCompact = false sets HIVE_COMPACT_WATERMARK_TOKENS=0, which the percent resolver still honours as a disable. Useful for large-context models (sonnet/opus) where the 75% heuristic fires before the session is actually full — the reactive path (compact-on-overflow at the hard limit) still applies.

• Auto session-reset — a third path (turn::maybe_auto_reset, pre-turn) that fires when both conditions hold: context is ≥ a watermark (HIVE_AUTO_RESET_WATERMARK_TOKENS, default 50% of context_window_tokens(model)) AND the time since the last turn exceeds the assumed prompt-cache TTL (HIVE_CACHE_TTL_SECS, default 3600). Claude's prompt cache goes cold after a while; once it's cold, --resume-ing a large session pays the full re-upload cost with no benefit over starting fresh. drive_turn archives the current session (same mechanism as the operator reset — rename <uuid>.jsonl → .archived) so the next turn's --resume <title> misses and starts fresh. Unlike proactive compaction the session is dropped entirely, not compacted — and no preceding checkpoint turn runs, because any turn before the reset would just re-warm the cache and defeat the purpose. Set HIVE_AUTO_RESET_WATERMARK_TOKENS=0 to disable. Autoreset and the operator reset are mutually exclusive per turn (both archive → fresh turn), so an explicit operator reset short-circuits the heuristic.

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 autoload 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: the popped message's from/body, prefixed with a [msg #<id>] broker-row-id marker (so the agent knows what id to pass to ack_until for bulk triage; transient pings show no marker because their sentinel id 0 has nothing to ack), 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, your session is intact." The next turn picks it up like any other inbox message.

On-boot files

hive-agent's turn module writes two files into its own per-service runtime dir, /run/hive-config/ (RuntimeDirectory = "hive-config", deliberately separate from /run/hive/, the host-owned dir holding the per-agent socket — so the harness owns this write surface and nothing needs to chown a bind mount), once at startup:

• claude-mcp-config.json — points claude at the persistent hive-mcp-http daemon (http://127.0.0.1:{port}/mcp, port from hyperhive.mcp.httpPort, default 8790) for the built-in hyperhive surface. HTTP is the sole transport for it — no per-turn stdio child, so the URL survives the per-turn claude re-spawn (no re-registration race), trading that for a hard dependency on the daemon's uptime (Restart=always, no stdio fallback). Extra servers stay stdio.

• claude-system-prompt.md — rendered from hive-agent/prompts/system.md by hive-agent's prompt::render: HTML-comment markers (<!-- role:agent -->...<!-- /role:agent -->, same for role:manager) gate the role-specific blocks; everything else is shared. Five placeholders are then substituted: {label} (short agent name), {qualified_label} (hive-qualified name@domain form), {operator_pronouns}, {hive_identity} (for example on hive `pr1ma`; empty when hyperhive.hiveName is unset), and {swarm_identity} (same shape for the swarm). Pronouns come from HIVE_OPERATOR_PRONOUNS env (set by the meta flake from services.hyperhive.c0re.operatorPronouns, default she/her). When hyperhive.docs.enable is set, HIVE_DOCS_DIR is present in the environment and render() appends a one-sentence pointer telling the agent the docs are mounted at that path. Passed via --system-prompt-file.

  Marker grammar. <!-- role:X --> opens a block; any <!-- /role:X --> closes the current block. The renderer always uses role agent, so blocks with other role tags are elided. Nesting is NOT supported — a stray opener with no closer runs until end of file. Whitespace inside markers is tolerated (<!--role:foo--> parses the same as <!-- role:foo -->). Content outside any marker is always included. Today's system.md carries no markers (single agent role) — the grammar stays wired for a future manager / multi-role prompt.

  hive_identity / swarm_identity shape. Each carries a leading space + backticked name ( on hive \pr1ma`, in swarm `constellat1on`) when the corresponding env var is set, otherwise empty string. The independence lets the template drop one or both into the opener prose without breaking single-hive deployments that never set the option; the renderer also treats Some("")from a caller asNone` so empty-string env vars and missing env vars round-trip the same way.

The per-turn plumbing described on this page — on-boot files, session identity, the reset/autoreset/retry state machine, and the telemetry-to-bus bridge — lives in hive-agent's turn module; see its //! doc comment (hive-agent/src/turn.rs) for the exact call shape. The actual claude spawn, stream classification, and the reactive/proactive compaction loop are in the hive-claude crate. Login-wait lives in hive-agent's login module.