diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 0021146d22..b258de84c6 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -48,6 +48,7 @@ concurrency:
 permissions:
   contents: read
   issues: write
+  pull-requests: write
 
 jobs:
   build-windows-kernel:
@@ -197,6 +198,22 @@ jobs:
         $ManifestPath = ".\src\manifest\MsQuicEtw.man"
         wevtutil.exe um $ManifestPath
         wevtutil.exe im $ManifestPath /rf:$($MsQuicDll) /mf:$($MsQuicDll)
+    - name: System Diagnostics (pre-test)
+      if: matrix.vec.plat == 'linux' && matrix.vec.xdp == '-UseXdp'
+      run: |
+        echo "=== Memory ==="
+        free -h
+        echo "=== Disk ==="
+        df -h / /tmp
+        echo "=== Kernel / XDP ==="
+        uname -r
+        sudo dmesg -T 2>/dev/null | tail -30 || true
+        echo "=== Core pattern ==="
+        cat /proc/sys/kernel/core_pattern || true
+        echo "=== ulimits ==="
+        ulimit -a
+        echo "=== CPU ==="
+        nproc && cat /proc/loadavg
     - name: Test
       if: matrix.vec.os == 'WinServerPrerelease'
       shell: pwsh
@@ -206,6 +223,8 @@ jobs:
       if: matrix.vec.os != 'WinServerPrerelease'
       shell: pwsh
       timeout-minutes: 120
+      env:
+        GITHUB_TOKEN: ${{ github.token }}
       run: scripts/test.ps1 -Config ${{ matrix.vec.config }} -Arch ${{ matrix.vec.arch }} -Tls ${{ matrix.vec.tls }} -OsRunner ${{ matrix.vec.os }} -GHA -LogProfile ${{ matrix.vec.log || (inputs.log_level || 'Full.Light') }} -GenerateXmlResults ${{ matrix.vec.xdp }} ${{ matrix.vec.qtip }} ${{ inputs.filter && '-Filter' }} ${{ inputs.filter || '' }}
     - name: Fix log permissions for Linux XDP
       if: failure() && matrix.vec.plat == 'linux' # (matrix.vec.plat == 'linux' && matrix.vec.xdp == '-UseXdp') doesn't work for some reason
diff --git a/scripts/test.ps1 b/scripts/test.ps1
index f164c14639..62e4608d2a 100644
--- a/scripts/test.ps1
+++ b/scripts/test.ps1
@@ -375,7 +375,151 @@ for ($iteration = 1; $iteration -le $NumIterations; $iteration++) {
     foreach ($TestPath in $TestPaths) {
         if ($IsLinux -and $UseXdp) {
             $NOFILE = Invoke-Expression "bash -c 'ulimit -n'"
-            Invoke-Expression ('/usr/bin/sudo bash -c "ulimit -n $NOFILE && pwsh $RunTest -Path $TestPath $TestArguments"')
+            $DiagDir = Join-Path $RootDir "artifacts" "xdp_diagnostics"
+            New-Item -ItemType Directory -Path $DiagDir -Force | Out-Null
+            $DiagFile = Join-Path $DiagDir "resource_monitor.log"
+            $BinaryName = Split-Path $TestPath -Leaf
+
+            # Helper: post a diagnostic comment to the PR via GitHub API.
+            function Post-XdpDiag($Title, $Body) {
+                if (-not $env:GITHUB_TOKEN -or -not $env:GITHUB_REPOSITORY) {
+                    Write-Host ">>> [XDP Diag] Missing GITHUB_TOKEN or GITHUB_REPOSITORY"
+                    return
+                }
+                if (-not ($env:GITHUB_REF -match 'refs/pull/(\d+)')) {
+                    Write-Host ">>> [XDP Diag] Not a PR (REF=$($env:GITHUB_REF))"
+                    return
+                }
+                $PrNum = $Matches[1]
+                $Full = "### XDP Diag: $Title`n$Body"
+                $TmpFile = Join-Path $DiagDir "comment.json"
+                @{ body = $Full } | ConvertTo-Json -Depth 2 | Set-Content -Path $TmpFile
+                $result = bash -c "curl -sS -w '%{http_code}' -X POST -H 'Authorization: Bearer $($env:GITHUB_TOKEN)' -H 'Content-Type: application/json' -d @$TmpFile 'https://api.github.com/repos/$($env:GITHUB_REPOSITORY)/issues/$PrNum/comments' -o /dev/null 2>&1"
+                Write-Host ">>> [XDP Diag] Post '$Title' to PR #$PrNum -> HTTP $result"
+            }
+
+            # Post pre-flight diagnostics BEFORE the test binary starts
+            $PreDiag = bash -c "echo 'mem:'; free -h | head -2; echo 'disk:'; df -h / | tail -1; echo 'load:'; cat /proc/loadavg; echo 'cores:'; nproc; echo 'kernel:'; uname -r"
+            Post-XdpDiag "Starting $BinaryName" "``````n$($PreDiag -join "`n")`n``````"
+
+            # Start background resource monitor that writes to a log file
+            $MonitorScript = Join-Path $DiagDir "monitor.sh"
+            @'
+#!/bin/bash
+while true; do
+    echo "[$(date +%H:%M:%S)] mem=$(free -m | awk 'NR==2{print $3"/"$2"MB"}') disk=$(df -h / | awk 'NR==2{print $3"/"$2}') load=$(cut -d' ' -f1-3 /proc/loadavg)" >> "$1"
+    sleep 30
+done
+'@ | Set-Content -Path $MonitorScript -NoNewline
+            bash -c "chmod +x $MonitorScript"
+            $MonitorPid = $null
+            try {
+                $MonitorPid = (Start-Process -FilePath "bash" -ArgumentList $MonitorScript, $DiagFile -PassThru -NoNewWindow).Id
+            } catch {
+                Write-Host "Warning: Could not start resource monitor: $_"
+            }
+
+            # Start background heartbeat only for msquictest (where the crash
+            # happens). Posts PR comments every 60 seconds so we capture the
+            # system state just before the runner crash.
+            $HeartbeatPid = $null
+            if ($BinaryName -eq "msquictest") {
+            $HeartbeatScript = Join-Path $DiagDir "heartbeat.sh"
+            @"
+#!/bin/bash
+BINARY_NAME="$BinaryName"
+DIAG_DIR="$DiagDir"
+DIAG_FILE="$DiagFile"
+"@ | Set-Content -Path $HeartbeatScript -NoNewline
+            @'
+
+COUNTER=0
+while true; do
+    COUNTER=$((COUNTER + 1))
+    # Collect system state
+    MEM=$(free -h | head -2)
+    DISK=$(df -h / | tail -1)
+    LOAD=$(cat /proc/loadavg)
+    # Broad dmesg check: kernel oops, BUG, OOM, XDP, segfault, panic, hung_task, slab
+    DMESG=$(sudo dmesg -T --since '2 minutes ago' 2>/dev/null | grep -iE 'oom|kill|xdp|bpf|segfault|oops|BUG|panic|Call Trace|RIP:|WARNING|hung_task|page allocation|slab|out of memory' | tail -20)
+    if [ -z "$DMESG" ]; then
+        DMESG="(no relevant kernel messages)"
+    fi
+    # Get last 5 lines of resource monitor
+    MONITOR_TAIL=""
+    if [ -f "$DIAG_FILE" ]; then
+        MONITOR_TAIL=$(tail -5 "$DIAG_FILE")
+    fi
+    # Get process tree for test processes (top 10 by memory)
+    PROCS=$(ps aux --sort=-%mem | head -10)
+    # Check kernel memory (slab + page cache details)
+    KMEM=$(cat /proc/meminfo | grep -E 'Slab|SReclaimable|SUnreclaim|Committed_AS|VmallocUsed|AnonPages|Mapped|PageTables')
+    # Build the comment body
+    BODY="### XDP Heartbeat #${COUNTER}: ${BINARY_NAME} (+${COUNTER} min)
+\`\`\`
+mem:
+${MEM}
+kernel mem:
+${KMEM}
+disk:
+${DISK}
+load:
+${LOAD}
+dmesg (last 2 min):
+${DMESG}
+top processes by memory:
+${PROCS}
+resource monitor:
+${MONITOR_TAIL}
+\`\`\`"
+    # Post to PR if possible
+    if [ -n "$GITHUB_TOKEN" ] && [ -n "$GITHUB_REPOSITORY" ] && [ -n "$GITHUB_REF" ]; then
+        PR_NUM=$(echo "$GITHUB_REF" | grep -oP 'refs/pull/\K\d+')
+        if [ -n "$PR_NUM" ]; then
+            TMPFILE="${DIAG_DIR}/heartbeat_comment.json"
+            python3 -c "import json,sys; print(json.dumps({'body': sys.stdin.read()}))" <<< "$BODY" > "$TMPFILE"
+            curl -sS -w '%{http_code}' -X POST \
+                -H "Authorization: Bearer $GITHUB_TOKEN" \
+                -H "Content-Type: application/json" \
+                -d @"$TMPFILE" \
+                "https://api.github.com/repos/$GITHUB_REPOSITORY/issues/$PR_NUM/comments" \
+                -o /dev/null 2>&1
+        fi
+    fi
+    sleep 60  # heartbeat every 60 seconds
+done
+'@ | Add-Content -Path $HeartbeatScript -NoNewline
+            bash -c "chmod +x $HeartbeatScript"
+            try {
+                $HeartbeatPid = (Start-Process -FilePath "bash" -ArgumentList $HeartbeatScript -PassThru -NoNewWindow).Id
+                Write-Host ">>> [XDP Diag] Heartbeat monitor started (PID=$HeartbeatPid) for $BinaryName"
+            } catch {
+                Write-Host "Warning: Could not start heartbeat monitor: $_"
+            }
+            } # end if msquictest
+
+            Write-Host ">>> [XDP Diag] Before ${BinaryName}:"
+            bash -c "free -h; echo '---'; df -h / /tmp; echo '---'; cat /proc/loadavg"
+            # Disable core dumps entirely via hard limit. Use timeout as
+            # a safety net.
+            Invoke-Expression ('/usr/bin/sudo bash -c "ulimit -n $NOFILE && ulimit -Hc 0 && timeout --signal=KILL --foreground 6000 pwsh $RunTest -Path $TestPath $TestArguments"')
+            $TestExitCode = $LASTEXITCODE
+
+            # Post post-test diagnostics
+            $PostDiag = bash -c "echo 'mem:'; free -h | head -2; echo 'disk:'; df -h / | tail -1; echo 'load:'; cat /proc/loadavg; echo 'dmesg:'; sudo dmesg -T --since '2 hours ago' 2>/dev/null | grep -iE 'oom|kill|xdp|bpf|segfault|oops|BUG|panic|Call Trace|RIP:|WARNING|hung_task|page allocation|slab|out of memory' | tail -20 || echo 'none'"
+            $MonitorLog = if (Test-Path $DiagFile) { Get-Content $DiagFile -Raw } else { "no data" }
+            Post-XdpDiag "Finished $BinaryName (exit=$TestExitCode)" "``````n$($PostDiag -join "`n")`n``````n`nResource monitor:`n``````n$MonitorLog`n``````"
+
+            Write-Host ">>> [XDP Diag] After ${BinaryName} (exit=$TestExitCode):"
+            $PostDiag | ForEach-Object { Write-Host $_ }
+
+            # Stop the background monitors
+            if ($MonitorPid) {
+                Stop-Process -Id $MonitorPid -ErrorAction SilentlyContinue
+            }
+            if ($HeartbeatPid) {
+                Stop-Process -Id $HeartbeatPid -ErrorAction SilentlyContinue
+            }
         } else {
             Invoke-Expression ($RunTest + " -Path $TestPath " + $TestArguments)
         }