test(net): add network isolation harnesses and failure edge case coverage

tests/test-network-python.fish

@@ -0,0 +1,31 @@
+#!/usr/bin/env fish
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+# Isolated test suite for Python helper scripts network isolation and edge case mocking.
+# Exercises scripts/sync-labels.py under offline conditions with full mock coverage.
+#
+# Runs isolated (no # MODE: marker, defaulting to isolated).
+
+source (realpath (dirname (status filename)))/lib.fish
+
+section "python network isolation: sync-labels.py"
+
+set -l py_script $repo_root/tests/test_sync_labels.py
+check "tests/test_sync_labels.py exists" true (test -f $py_script; and echo true; or echo false)
+
+set -l py_lines (python3 $py_script -v 2>&1)
+set -l py_status $status
+
+for line in $py_lines
+    if string match -qr '^\s*(test_\w+)\s+\([^)]+\)\s+\.\.\.\s+(\w+)' -- $line
+        set -l match (string match -r '^\s*(test_\w+)\s+\([^)]+\)\s+\.\.\.\s+(\w+)' -- $line)
+        set -l tname $match[2]
+        set -l tres $match[3]
+        check "$tname" ok (string lower $tres)
+    end
+end
+
+check "test_sync_labels.py suite exited 0" 0 $py_status
+
+report