Every spawn class is wired through a capped-cgroup wrapper, but the exclusion list defaults to all of them unless CLAUDE_CODE_TOOL_MEMORY_CGROUP_EXCLUDE says otherwise.
On Linux and WSL, child processes started by Claude Code can now be placed into a memory-limited control group, so a runaway server or hook is killed at a cap instead of exhausting the host. This covers stdio MCP servers, LSP servers, hook runners, plugin installs, tmux agent sessions and the background terminal host, all launched through a wrapper that joins the capped group before running the real command. None of it is active in this build: the exclusion list falls back to a set containing every one of those classes, so the wiring is dark-launched unless CLAUDE_CODE_TOOL_MEMORY_CGROUP_EXCLUDE or server config says otherwise.
- The two shared process-spawning helpers now accept
useToolMemoryCgroupandtoolCgroupClassoptions, and plugin subprocesses pass thepluginclass. - A process started before the cgroup is ready has its process id parked and is adopted into the group once the group exists, rather than being lost track of.
- MCP capping has its own switch,
CLAUDE_CODE_MCP_MEMORY_CGROUPor failing that thetengu_mcp_memory_cgroupsetting; only an explicit false opts out, and when it resolves to disabled MCP is added to the exclusion list and no MCP server is capped. - Each MCP server process is registered against the cgroup by process id together with its start time read from /proc, rechecked whenever the set of hooks changes, so a stale process id cannot be mistaken for a live server.
- A capped MCP server is released from the cap just before a hook backed by that server fires, so the hook does not run against a constrained process; a fixed set of events skips this release path, including Notification, SessionStart, SessionEnd, Setup and StopFailure.
- Claude Code's own helpers deliberately opt out with
useToolMemoryCgroup: !1: npm update checks, the Linux clipboard helpers, the CA installer, AWS credential export, systemctl, xdg-open and "open project in IDE". - The external editor launch and the terminal host retry the spawn without the cgroup if the first attempt fails.
- When an LSP server dies by SIGKILL or exit 137 while capped, the crash message names the cause by appending
killed at the tool memory limit (CLAUDE_CODE_TOOL_MEMORY_LIMIT), or says "likely killed" when it cannot confirm the cause. - If the host has too little memory for the default cap, the feature disables itself and logs
tool cgroup: disabled (host too small for the default cap); thetool cgroup:log lines are all new in this build.
{ echo 0 > "$0"/cgroup.procs; } 2>/dev/null; exec "$@", toolCgroupClass, useToolMemoryCgroup: !1, useToolMemoryCgroup, tool cgroup: disabled (host too small for the default cap), killed at the tool memory limit (CLAUDE_CODE_TOOL_MEMORY_LIMIT), hook was still capped at fire time, let { useToolMemoryCgroup: r, toolCgroupClass: o, ...i } = n,
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
tengu_mcp_memory_cgroup Off in both readingsThe flag server returned off for the account this site reads and for the anonymous baseline. A reading of off cannot rule out a rollout these two readings sit outside of.
This account: off · anonymous baseline: off · compiled default in v2.1.246: not a boolean we can read
Read once, for one account on one subscription tier, against v2.1.246. It isn't a statement about your account. What a flag value here can and cannot tell you
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
New in this build: CLAUDE_CODE_TOOL_MEMORY_CGROUP_EXCLUDE