The TUI hardcoded --max-old-space-size=8192. V8 is not cgroup-aware, so in a
Docker/k8s container capped below ~9-10GB the heap grows past the container
limit and the cgroup OOM-killer SIGKILLs the Node parent BEFORE V8's own heap
monitor fires. SIGKILL runs no JS handler, writes no [tui-parent] breadcrumb,
and closes the gateway child's stdin — the user sees only a bare gateway
'stdin EOF'. Complements #38224 (trail-text cap), which reduced pressure but
left the 8GB-vs-container mismatch in place.
- _read_cgroup_memory_limit(): read cgroup v2 (memory.max) then v1
(memory.limit_in_bytes); handle 'max', the v1 unlimited sentinel, blank/zero,
and >=1PB as unconstrained.
- _resolve_tui_heap_mb(): unconstrained -> 8192; constrained -> 75% of the
cgroup limit (headroom for non-heap RSS + the Python child sharing the
cgroup), floored at 1536MB, never above 8192.
- NODE_OPTIONS block uses the sized value; still respects a user-supplied
--max-old-space-size.
Net: V8 now GCs/exits gracefully (onCritical breadcrumb fires) instead of being
reaped silently. Display/transport only — no agent context or behavior change.
Tests: tests/hermes_cli/test_tui_heap_sizing.py (20 tests).
