diff --git a/.github/scripts/diagnostic-quiet-build.sh b/.github/scripts/diagnostic-quiet-build.sh
new file mode 100644
index 0000000..1268ff8
--- /dev/null
+++ b/.github/scripts/diagnostic-quiet-build.sh
@@ -0,0 +1,121 @@
+#!/bin/bash
+set -euo pipefail
+
+log_dir=".buildchain/diagnostics"
+log_file="${log_dir}/quiet-build.log"
+process_context_file="${log_dir}/process-context.log"
+mkdir -p "${log_dir}"
+: > "${log_file}"
+: > "${process_context_file}"
+
+echo "quiet build stdout/stderr: ${log_file}"
+echo "quiet process context: ${process_context_file}"
+echo "quiet build started: $(date -u +%Y-%m-%dT%H:%M:%SZ)"
+
+ps_one() {
+  pid="$1"
+  ps -o pid=,ppid=,pgid=,sess=,tty=,stat=,nice=,pri=,user=,command= -p "${pid}" 2>/dev/null \
+    || ps -o pid=,ppid=,pgid=,tty=,stat=,nice=,user=,command= -p "${pid}" 2>/dev/null \
+    || true
+}
+
+parent_pid() {
+  pid="$1"
+  ps -o ppid= -p "${pid}" 2>/dev/null | awk '{print $1}' || true
+}
+
+collect_process_context() {
+  label="$1"
+  {
+    echo
+    echo "## process context: ${label}"
+    echo "timestamp: $(date -u +%Y-%m-%dT%H:%M:%SZ)"
+    echo "whoami: $(whoami 2>/dev/null || true)"
+    echo "pwd: $(pwd)"
+    echo "uname: $(uname -a 2>/dev/null || true)"
+    echo "shell: ${SHELL:-}"
+    echo "bash_pid: ${BASHPID:-}"
+    echo "shell_pid: $$"
+    echo "parent_pid: ${PPID:-}"
+    echo "stdout_is_tty: $(test -t 1 && echo yes || echo no)"
+    echo "stderr_is_tty: $(test -t 2 && echo yes || echo no)"
+    echo "github_actions: ${GITHUB_ACTIONS:-}"
+    echo "github_workflow: ${GITHUB_WORKFLOW:-}"
+    echo "github_job: ${GITHUB_JOB:-}"
+    echo "github_action: ${GITHUB_ACTION:-}"
+    echo "github_ref: ${GITHUB_REF:-}"
+    echo "github_sha: ${GITHUB_SHA:-}"
+    echo "runner_name: ${RUNNER_NAME:-}"
+    echo "runner_os: ${RUNNER_OS:-}"
+    echo "runner_arch: ${RUNNER_ARCH:-}"
+    echo "runner_temp: ${RUNNER_TEMP:-}"
+    echo "runner_workspace: ${RUNNER_WORKSPACE:-}"
+    echo
+    echo "### stdio fds"
+    ls -l /dev/fd/0 /dev/fd/1 /dev/fd/2 2>/dev/null || true
+    if command -v lsof >/dev/null 2>&1; then
+      lsof -a -p "$$" -d 0,1,2 2>/dev/null || true
+    fi
+    echo
+    echo "### parent chain"
+    current="$$"
+    depth=0
+    while [ -n "${current}" ] && [ "${current}" != "0" ] && [ "${depth}" -lt 16 ]; do
+      ps_one "${current}"
+      next="$(parent_pid "${current}")"
+      [ "${next}" = "${current}" ] && break
+      current="${next}"
+      depth=$((depth + 1))
+    done
+    echo
+    echo "### relevant process snapshot"
+    ps -axo pid=,ppid=,pgid=,sess=,tty=,stat=,nice=,pri=,user=,pcpu=,etime=,command= 2>/dev/null \
+      | grep -E 'Runner\\.|actions-runner|diagnostic-quiet-build|buildchain\\.mjs|node-make|make -j|make -C out|corepack pnpm|ccache|clang' \
+      | grep -v 'grep -E' \
+      || true
+  } >> "${process_context_file}" 2>&1
+}
+
+heartbeat() {
+  while true; do
+    sleep 60
+    echo "quiet build heartbeat: $(date -u +%Y-%m-%dT%H:%M:%SZ)"
+    collect_process_context "heartbeat"
+    if command -v ccache >/dev/null 2>&1; then
+      ccache --show-stats 2>/dev/null | sed -n '1,5p' || true
+    fi
+  done
+}
+
+collect_process_context "script-start"
+
+heartbeat &
+heartbeat_pid="$!"
+trap 'kill "${heartbeat_pid}" >/dev/null 2>&1 || true' EXIT
+
+run_quiet() {
+  name="$1"
+  shift
+  {
+    echo
+    echo "## ${name}"
+    echo "start: $(date -u +%Y-%m-%dT%H:%M:%SZ)"
+    printf '$'
+    printf ' %q' "$@"
+    echo
+  } >> "${log_file}"
+  echo "quiet build step start: ${name}"
+  collect_process_context "before-${name}"
+  "$@" >> "${log_file}" 2>&1
+  collect_process_context "after-${name}"
+  {
+    echo "end: $(date -u +%Y-%m-%dT%H:%M:%SZ)"
+  } >> "${log_file}"
+  echo "quiet build step end: ${name}"
+}
+
+run_quiet "make" corepack pnpm make
+run_quiet "build" node .gyp/run-with-env.js KF_SKIP_MAKE_LIBNODE=true -- corepack pnpm build
+run_quiet "package" corepack pnpm package
+
+echo "quiet build finished: $(date -u +%Y-%m-%dT%H:%M:%SZ)"
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index e28b42e..686c398 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -31,8 +31,12 @@ jobs:
       artifact-name-template: '{artifact}-{platform}-{sha}'
       artifact-paths: |
         build/stage
-      release-candidate: ${{ startsWith(github.base_ref, 'alpha/') }}
-      publish-channel: ${{ startsWith(github.base_ref, 'alpha/') && 'alpha' || 'none' }}
+      platforms-json: >-
+        ${{ github.event_name == 'pull_request' && startsWith(github.base_ref, 'alpha/') && github.head_ref == 'feature/macos-alpha-diagnostic' && '[{"id":"macos-arm64","name":"macOS ARM64","runner":"[\"self-hosted\",\"macOS\",\"ARM64\",\"kungfu-build-v4-macos-arm64\"]"}]' || '' }}
+      release-candidate: ${{ startsWith(github.base_ref, 'alpha/') && github.head_ref != 'feature/macos-alpha-diagnostic' }}
+      publish-channel: ${{ startsWith(github.base_ref, 'alpha/') && github.head_ref != 'feature/macos-alpha-diagnostic' && 'alpha' || 'none' }}
+      build-command: >-
+        ${{ github.event_name == 'pull_request' && startsWith(github.base_ref, 'alpha/') && github.head_ref == 'feature/macos-alpha-diagnostic' && 'bash .github/scripts/diagnostic-quiet-build.sh' || '' }}
       expected-artifacts-json: >-
         {"minFiles":1,"minTotalBytes":10000000}
       artifact-retention-days: 14
diff --git a/.gyp/node-make.js b/.gyp/node-make.js
index 19bf8b5..1aa9a97 100644
--- a/.gyp/node-make.js
+++ b/.gyp/node-make.js
@@ -38,6 +38,12 @@ function runCacheTool(tool, args) {
   run(tool, args, { check: false });
 }
 
+function showDirectorySize(label, dir) {
+  if (!dir || !fs.existsSync(dir) || process.platform === 'win32' || !commandExists('du')) return;
+  console.log(`compiler cache ${label} size:`);
+  runCacheTool('du', ['-sh', dir]);
+}
+
 function prepareUnixCompilerCache(mode) {
   if (mode === 'sccache') {
     const sccache = commandExists('sccache');
@@ -102,6 +108,16 @@ function showCompilerCacheStats() {
   }
 }
 
+function showCompilerCacheDiagnostics(stage) {
+  console.log(`compiler cache diagnostics (${stage}):`);
+  for (const name of ['KF_COMPILER_CACHE', 'KF_COMPILER_CACHE_ROOT', 'CCACHE_DIR', 'SCCACHE_DIR', 'CC', 'CXX']) {
+    console.log(`${name}=${process.env[name] || ''}`);
+  }
+  showDirectorySize('ccache dir', process.env.CCACHE_DIR);
+  showDirectorySize('sccache dir', process.env.SCCACHE_DIR);
+  showCompilerCacheStats();
+}
+
 function cleanNodeBuildState() {
   const generatedPaths = ['out', 'Release', 'Debug', 'config.gypi', 'config.mk'];
   for (const entry of generatedPaths) {
@@ -190,18 +206,20 @@ const buildWin = () => {
   cleanNodeBuildState();
   prepareWindowsPythonEnv();
   const cacheArgs = prepareCompilerCache();
+  showCompilerCacheDiagnostics('before build');
   run(path.join('.', 'vcbuild.bat'), ['dll', arch, 'release', 'projgen', 'nobuild', ...cacheArgs], { cwd: nodeSrcDir });
   runWinPatch();
   run(path.join('.', 'vcbuild.bat'), ['dll', 'noprojgen', ...cacheArgs], { cwd: nodeSrcDir });
-  showCompilerCacheStats();
+  showCompilerCacheDiagnostics('after build');
 };
 
 const buildUnix = () => {
   cleanNodeBuildState();
   prepareCompilerCache();
+  showCompilerCacheDiagnostics('before build');
   run('sh', [path.join('.', 'configure'), '--shared'], { cwd: nodeSrcDir });
   run('make', ['-j', `${buildJobs()}`], { cwd: nodeSrcDir });
-  showCompilerCacheStats();
+  showCompilerCacheDiagnostics('after build');
 };
 
 const build = process.platform === 'win32' ? buildWin : buildUnix;