diff --git a/.github/workflows/hrx-build.yml b/.github/workflows/hrx-build.yml
index 15d55c191..6478a59ae 100644
--- a/.github/workflows/hrx-build.yml
+++ b/.github/workflows/hrx-build.yml
@@ -39,6 +39,11 @@
 # comments, blanks) configures with ONEBIT_HRX=ON and skips the compile: such a line creates no target and sets
 # no flag, but it is still evaluated at configure time, including inside if(ONEBIT_HRX) blocks ci.yml never
 # configures. tools/ci/hrx_build_scope.py decides; anything it does not recognise builds.
+# Memory (engine#1504): the box is shared and its GTT is host RAM, and on 2026-11-08 both runners were OOM-killed,
+# the second time 76 s after a restart that handed this job a compile. So the compile waits for MemAvailable to
+# reach a floor (scripts/mem-wait.sh, up to 15 min, then the job fails and says why), and it runs under
+# scripts/mem-guard.sh --term, which ends the whole thermal-run scope before the kernel's OOM killer picks
+# someone else's process.
 # Fork PRs never reach the box: the `if:` requires the head repository to be this one.
 name: hrx-build
 
@@ -111,13 +116,20 @@ jobs:
         if: steps.scope.outputs.build != 'true'
         run: echo "only test registration changed in CMakeLists.txt; the ONEBIT_HRX=ON configure above passed, the compile is skipped" | tee -a "$GITHUB_STEP_SUMMARY"
 
+      - name: Wait for memory (or refuse)
+        if: steps.scope.outputs.build == 'true'
+        timeout-minutes: 20
+        # 24 GB free before a 4-core compile starts; it is stopped if the box drops under 12 GB (hw-gate's floor)
+        run: scripts/mem-wait.sh 24 15
+
       - name: Build llama_hrx and onebit
         if: steps.scope.outputs.build == 'true'
         env:
           CCACHE_BASEDIR: ${{ github.workspace }}
         run: |
           set -euo pipefail
-          ~/lb/thermal-run.sh cmake --build "$HRX_BUILD" --target onebit -j 4
+          # the guard outside thermal-run: SIGTERM makes thermal-run end its whole scope (ninja and the compilers)
+          scripts/mem-guard.sh --term 12 ~/lb/thermal-run.sh cmake --build "$HRX_BUILD" --target onebit -j 4
           # the build must have produced the HRX backend and the server onebit runs
           ls -l "$HRX_BUILD"/hrx/llama/bin/llama-server
           find "$HRX_BUILD"/hrx/llama -name 'libggml-hrx.so*' -print -quit | grep .
diff --git a/docs/hw-gate.md b/docs/hw-gate.md
index f7c06fcb7..9ad7bfeb2 100644
--- a/docs/hw-gate.md
+++ b/docs/hw-gate.md
@@ -63,6 +63,11 @@ hrx-system) through `cmake/hrx.cmake`, then links `onebit` with its HRX wiring.
   while every PR-Agent review queued behind it. It takes no GPU token and no NPU lock. Fork PRs never run it. It costs
   no GitHub Actions minutes. The token is read-only, and the build tree persists in `~/.cache/hrx-build/bench` on the
   box, so a later run rebuilds only what changed.
+- **Memory.** The box is shared, and on Strix Halo GTT is host RAM. Before it compiles, the job waits for 24 GB of
+  `MemAvailable` (`scripts/mem-wait.sh`, polled once a minute for up to 15 minutes). If memory doesn't free up, the job
+  fails with the reading, and a re-run is the fix. The compile itself runs under `scripts/mem-guard.sh --term 12`,
+  which stops the whole `thermal-run` scope if `MemAvailable` falls below 12 GB. On 2026-11-08 both self-hosted
+  runners were OOM-killed, the second time 76 s after a restart handed this job a compile (engine#1504).
 - **What it is not.** It is a compile and link check of the public plumbing only. It does not build the private HIP
   add-on (the gate builds that) and does not dispatch anything. Green means the pinned pair builds into the engine. It
   does not replace the `hw-gate` label on a pin bump.
diff --git a/scripts/mem-guard.sh b/scripts/mem-guard.sh
index e6193f0ec..1a7e35e59 100755
--- a/scripts/mem-guard.sh
+++ b/scripts/mem-guard.sh
@@ -14,14 +14,25 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-# mem-guard.sh <min_available_gb> <cmd...>: run cmd and kill it if MemAvailable drops below
+# mem-guard.sh [--term] <min_available_gb> <cmd...>: run cmd and kill it if MemAvailable drops below
 # the floor, before the kernel's OOM killer picks other processes (GPU allocations on Strix
 # Halo's unified memory escape cgroup limits, so MemoryMax alone does not protect the box).
+# --term sends SIGTERM first and SIGKILL 10 s later. Use it when cmd is ~/lb/thermal-run.sh: a
+# SIGKILL'd thermal-run cannot run its trap, so its scope (ninja and every compiler under it) keeps
+# running and keeps the memory; on SIGTERM it kills the whole scope (engine#1504).
+term=0; [ "$1" = --term ] && { term=1; shift; }
 floor=$1; shift
 "$@" & pid=$!
 while kill -0 $pid 2>/dev/null; do
   avail=$(awk '/MemAvailable/ {print int($2/1048576)}' /proc/meminfo)
-  if [ "$avail" -lt "$floor" ]; then echo "GUARD: MemAvailable ${avail} GB < ${floor} GB, killing $pid" >&2; kill -9 $pid; fi
+  if [ "$avail" -lt "$floor" ]; then
+    echo "GUARD: MemAvailable ${avail} GB < ${floor} GB, killing $pid" >&2
+    if [ $term = 1 ]; then
+      kill -TERM $pid
+      for _ in $(seq 20); do kill -0 $pid 2>/dev/null || break; sleep 0.5; done
+    fi
+    kill -9 $pid 2>/dev/null
+  fi
   sleep 0.5
 done
 wait $pid
diff --git a/scripts/mem-wait.sh b/scripts/mem-wait.sh
new file mode 100755
index 000000000..00ce6df3b
--- /dev/null
+++ b/scripts/mem-wait.sh
@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+# Copyright 2026 bong-water-water-bong
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# mem-wait.sh <min_available_gb> <max_wait_min>: return 0 once MemAvailable is at least the floor; poll once a
+# minute and give up with exit 75 after max_wait_min. A preflight for a heavy job on the shared box: starting a
+# compile into an exhausted box is what turned one OOM into two on 2026-11-08 (engine#1504; both self-hosted
+# runners were OOM-killed 76 s after a restart, with 0 swap free). Each poll prints what the box looks like, so a
+# refusal says why. The floor is MemAvailable only: on this APU GTT is host RAM, and MemAvailable already counts it.
+floor=${1:?usage: mem-wait.sh <min_available_gb> <max_wait_min>}; max=${2:?usage: mem-wait.sh <min_available_gb> <max_wait_min>}
+meminfo() { awk -v k="$1" '$1 == k":" {print int($2/1048576)}' /proc/meminfo; }
+for i in $(seq 0 "$max"); do
+  avail=$(meminfo MemAvailable)
+  line="MemAvailable ${avail} GB (floor ${floor} GB), swap free $(meminfo SwapFree) of $(meminfo SwapTotal) GB"
+  if [ "$avail" -ge "$floor" ]; then echo "mem-wait: ok: $line"; exit 0; fi
+  [ "$i" = "$max" ] && break
+  echo "mem-wait: waiting ($((i + 1)) of $max min): $line"
+  sleep 60
+done
+echo "mem-wait: REFUSED after ${max} min: $line. The box is short of memory, so this job did not start its build;" \
+     "re-run it once memory frees (engine#1504)." >&2
+exit 75