Sweep leaked test networks at job start

.github/workflows/test.yml

@@ -54,6 +54,31 @@ jobs:
             -e lib/ingress/binaries/ \
             -e bin/
 
+      # Tests create a bridge and route per VM and clean up on success, but a
+      # run that dies mid-test (crash, timeout, superseded-run cancellation)
+      # leaks them, and enough leaked routes fail new tests on subnet
+      # conflicts. Each job sweeps before it starts. A live bridge can sit
+      # DOWN with no ports for minutes (Initialize creates it, the TAP only
+      # attaches after the rootfs build), so liveness alone cannot identify
+      # a leak; age can: a live bridge waits at most one go-test timeout for
+      # its TAP, while leaks are hours old. The sysfs dir timestamp is the
+      # interface's creation time, and a failed stat spares the interface.
+      # Nothing here ever fails the job.
+      - name: Clean leaked test networks
+        run: |
+          cutoff=$(( $(date +%s) - 3600 ))
+          ip -br link show | awk '$1 ~ /^(h[0-9a-f]{8}|hi[0-9a-f]+|hm[0-9a-f]+|hype-[a-z0-9]+)$/ && $2 == "DOWN" {print $1}' |
+          while read -r ifc; do
+            if [ -z "$(ls "/sys/class/net/$ifc/brif" 2>/dev/null)" ] \
+               && [ "$(stat -c %Y "/sys/class/net/$ifc" 2>/dev/null || echo "$cutoff")" -lt "$cutoff" ]; then
+              echo "$ifc"
+            fi
+          done > "$RUNNER_TEMP/net-sweep-dead"
+          while read -r ifc; do
+            sudo ip link del "$ifc" 2>/dev/null || true
+          done < "$RUNNER_TEMP/net-sweep-dead"
+          echo "swept $(wc -l < "$RUNNER_TEMP/net-sweep-dead") interfaces (DOWN, portless, older than 1h)"
+
       - name: Set up Go
         uses: actions/setup-go@v6
         with: