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agents: read the memory cap at boot, not from the build

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An agent's memory cap was rendered into its flake (`memoryMaxBytes` →
`services.hyperhive.agent.claudeMemoryMaxBytes`), so the closure depended
on it and a changed cap reached the JSC heap ceiling and the subagent
`MemoryHigh=` only after a rebuild.

hive-c0re now writes the effective `MemoryMax=` in bytes to the agent's
runtime dir (`/run/hive/memory-max-bytes` inside) in `write_dropins`,
from the same value the drop-in gets. The file is removed for
`infinity` or a RAM percentage, and left alone when the drop-in is kept.

Inside the container, `nix/agent-modules/memory-cap.nix` reads it at
boot: an environment generator sets `BUN_JSC_forceRAMSize` (75%) for
every unit and `machinectl shell`, `/etc/set-environment` exports it in
login shells, and a unit generator writes `MemoryHigh=` (2/3) as a
drop-in for `hive-subagent-daemon`.

The render drops `memoryMaxBytes`, the agent option is removed (both
spellings fail eval with a removal message), and
`effective_memory_bytes_from` goes with its only caller.

Part of #5081 (slice S0-2).
This commit is contained in:
atlas 2026-10-12 09:00:45 +02:00
commit 0d619e215e
15 changed files with 416 additions and 287 deletions
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24
nix/agent-modules/mcp.nix
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@ -11,25 +11,6 @@
}:
let
userName = config.services.hyperhive.agent.user.name;
# This container's own effective `MemoryMax=` in bytes, baked in per
# agent by meta.rs's flake render — see
# `services.hyperhive.agent.claudeMemoryMaxBytes` in ./claude-settings.nix. `null`
# when the cap is `infinity` or a RAM percentage, i.e. when the module
# has no byte count to size anything against.
containerMemoryMaxBytes = config.services.hyperhive.agent.claudeMemoryMaxBytes;
# Two thirds of the container's cap, as the soft ceiling on everything
# the subagent daemon runs. The daemon spawns nested `claude` sessions
# as plain children, so its cgroup already *is* the "all subagents"
# cgroup and a unit-level ceiling bounds the set without a slice.
#
# `MemoryHigh=` and not `MemoryMax=`: this throttles rather than walls.
# Past it the kernel reclaims aggressively and the cgroup stalls, so a
# subagent that overshoots gets visibly slow and the remaining third
# stays available for the agent's own turn — but a subagent that
# genuinely needs more than two thirds still gets it when the container
# has the memory to spare, which is what keeps overprovisioning
# (several agents that rarely compile at the same time) working.
subagentMemoryHigh = containerMemoryMaxBytes * 2 / 3;
# Set on the harness only for an ACP agent on the opencode preset
# (./agent-service.nix).
acpApiKeyEnv = config.systemd.services.hive-agent.environment.HIVE_ACP_API_KEY_ENV or null;
@ -475,12 +456,11 @@ in
# actually chose and leaves the daemon serving, which is also what
# lets it report the kill rather than vanish and be restarted.
OOMPolicy = "continue";
# `MemoryHigh=` is a drop-in from ./memory-cap.nix, sized at boot from
# the container's cap.
User = userName;
Group = userName;
}
// lib.optionalAttrs (containerMemoryMaxBytes != null) {
MemoryHigh = toString subagentMemoryHigh;
}
// lib.optionalAttrs subagentReadsStore {
# Bare id: inherits the credential the container manager passed in,
# the same form ./queue-identity.nix uses.