onboard-spoke.sh: replace grep -A5 union duplicate check with python3 for reliable section parsing

hub/onboard-spoke.sh

@@ -169,7 +169,24 @@ if [[ "${ADD_UNION,,}" == "y" ]]; then
         UPSTREAM="${SPOKE_NAME}-remote:${UPSTREAM_TAG}"
     fi
     if grep -q "^\[${UNION_NAME}\]" "$RCLONE_CONF" 2>/dev/null; then
-        if grep -A5 "^\[${UNION_NAME}\]" "$RCLONE_CONF" | grep -qF "${SPOKE_NAME}-remote:"; then
+        ALREADY=$(python3 - "$RCLONE_CONF" "$UNION_NAME" "${SPOKE_NAME}-remote:" <<'PYEOF'
+import sys
+path, section, prefix = sys.argv[1], sys.argv[2], sys.argv[3]
+with open(path) as f:
+    lines = f.readlines()
+in_section = False
+for line in lines:
+    if line.strip() == f"[{section}]":
+        in_section = True
+    elif line.strip().startswith("["):
+        in_section = False
+    if in_section and line.startswith("upstreams =") and prefix in line:
+        print("yes")
+        raise SystemExit
+print("no")
+PYEOF
+)
+        if [ "$ALREADY" = "yes" ]; then
             warn "Upstream for ${SPOKE_NAME}-remote already in union remote [${UNION_NAME}], skipping."
         else
             python3 - "$RCLONE_CONF" "$UNION_NAME" "$UPSTREAM" <<'PYEOF'