diff --git a/patch/patch_ui.py b/patch/patch_ui.py
index d2b4d69..46117df 100644
--- a/patch/patch_ui.py
+++ b/patch/patch_ui.py
@@ -9,8 +9,8 @@ in the minified JS in one of two forms depending on TrueNAS / Angular version:
   TrueNAS 24.x (static inline array):
       "filterByProviders",["STORJ_IX"]
 
-  TrueNAS 25.x+ (Angular pureFunction binding):
-      "filterByProviders",pe(115,Rn,i.CloudSyncProviderName.Storj)
+  TrueNAS 25.x+ (Angular pureFunction binding, inside a chained property call):
+      c(2,"filterByProviders",pe(115,Rn,i.CloudSyncProviderName.Storj))("required",!0)
 
 Both are replaced so the dropdown includes S3 and B2. The file is backed up
 before modification so uninstall.sh can restore it.
@@ -33,11 +33,21 @@ WEBUI_CANDIDATES = [
 # Patterns tried in order; the first match wins.
 # Each entry is (compiled_regex, replacement_string).
 _PATTERNS = [
-    # TrueNAS 25.x+: Angular emits a pureFunction call instead of a literal array.
+    # TrueNAS 25.x+: Angular emits a pureFunction call instead of a literal array,
+    # inside a CHAINED property binding — so the call is followed by two closing
+    # parens, one for pe(...) and one for the property(...) it sits in:
+    #
+    #     c(2,"filterByProviders",pe(115,Rn,i.CloudSyncProviderName.Storj))("required",!0)
+    #                                                                    ^^
+    # The pattern consumes both and re-emits one, leaving the paren balance
+    # unchanged. Getting that wrong is a syntax error in the bundle and the whole
+    # web UI goes blank — see tests/test_patch_ui.py.
+    #
+    # The minified names (pe / slot index / Rn / i) change across builds;
+    # CloudSyncProviderName.Storj is stable because it is a TypeScript enum name.
     (re.compile(r'("filterByProviders",)\w+\(\d+,\w+,\w+\.CloudSyncProviderName\.Storj\)\)'),
      r'\1["STORJ_IX","S3","B2"])'),
 
-
     # TrueNAS 24.x and earlier: static inline array.
     (re.compile(r'("filterByProviders",)\["STORJ_IX"\]'),
      r'\1["STORJ_IX","S3","B2"]'),
diff --git a/tests/test_patch_ui.py b/tests/test_patch_ui.py
new file mode 100644
index 0000000..950b28e
--- /dev/null
+++ b/tests/test_patch_ui.py
@@ -0,0 +1,113 @@
+"""Tests for the Angular bundle patch.
+
+This is the one part of the patch that edits *minified third-party JavaScript* by
+regex, so it is the easiest place to silently produce a broken bundle: a pattern
+that matches nothing leaves the dropdown Storj-only, and a pattern that matches
+sloppily can unbalance the parentheses and take the whole web UI down.
+
+Nothing checked it until now. The snippets below are verbatim from a real
+TrueNAS 25.x bundle (chunk-*.js, pre-patch).
+"""
+
+import os
+import re
+import sys
+
+import pytest
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "patch"))
+
+from patch_ui import MARKER, _PATTERNS, _match_pattern  # noqa: E402
+
+# Verbatim from /usr/share/truenas/webui/chunk-FX2QXNQU.js on TrueNAS 25.10.
+# Angular emits the binding as a chained ɵɵproperty(...)(...) call, so the
+# pureFunction call is followed by TWO closing parens: one for pe(...), one for
+# property(...).
+REAL_25X = (
+    'c(2,"filterByProviders",pe(115,Rn,i.CloudSyncProviderName.Storj))'
+    '("required",!0),r(3'
+)
+
+# TrueNAS 24.x and earlier emitted a literal array.
+REAL_24X = 'c(2,"filterByProviders",["STORJ_IX"])("required",!0),r(3'
+
+
+def apply_patch(content):
+    """Run the same match-and-substitute main() does."""
+    find, replace = _match_pattern(content)
+    assert find is not None, "no pattern matched"
+    patched, count = find.subn(replace, content)
+    return patched, count
+
+
+def paren_delta(s):
+    """Net paren balance. The snippets are fragments of a minified file, so they
+    are not balanced on their own -- what must hold is that patching does not
+    CHANGE the balance. Consuming one paren too many is a syntax error in the
+    bundle, and the whole TrueNAS web UI goes blank."""
+    return s.count("(") - s.count(")")
+
+
+@pytest.mark.parametrize("source", [REAL_25X, REAL_24X], ids=["25.x", "24.x"])
+class TestAgainstRealBundles:
+    def test_matches_exactly_once(self, source):
+        # main() refuses to write unless count == 1 — more than one match would
+        # mean the pattern is too loose to trust against a minified bundle.
+        _patched, count = apply_patch(source)
+        assert count == 1
+
+    def test_result_contains_all_three_providers(self, source):
+        patched, _ = apply_patch(source)
+        assert MARKER in patched
+        assert '"filterByProviders",["STORJ_IX","S3","B2"]' in patched
+
+    def test_patch_does_not_change_paren_balance(self, source):
+        # Consuming one paren too many (or too few) is a syntax error in the
+        # bundle and the entire TrueNAS web UI goes blank. This is the invariant
+        # the 25.x pattern has to get right: it eats `pe(...)` which sits inside
+        # a chained property(...)(...) call.
+        patched, _ = apply_patch(source)
+        assert paren_delta(patched) == paren_delta(source)
+
+    def test_surrounding_code_is_untouched(self, source):
+        patched, _ = apply_patch(source)
+        assert patched.startswith("c(2,")
+        assert patched.endswith('("required",!0),r(3')
+
+    def test_patch_is_idempotent(self, source):
+        # apply.sh re-runs every boot; MARKER short-circuits an already-patched
+        # file, but the pattern must also not match its own output.
+        patched, _ = apply_patch(source)
+        find, _replace = _match_pattern(patched)
+        if find is not None:
+            # Only the 24.x literal-array pattern may still "match" — and only if
+            # it would produce the same text. Anything else means double-patching.
+            again, _ = apply_patch(patched)
+            assert again == patched, "re-patching must be a no-op"
+
+
+def test_storj_only_bundle_is_recognised():
+    assert _match_pattern(REAL_25X)[0] is not None
+
+
+def test_unrelated_javascript_is_never_touched():
+    # A pattern loose enough to hit unrelated code would corrupt the bundle.
+    for noise in (
+        'c(2,"filterByProviders",pe(115,Rn,i.SomethingElse.Storj))',
+        'c(2,"otherBinding",pe(115,Rn,i.CloudSyncProviderName.Storj))',
+        '"filterByProviders"',
+    ):
+        find, _ = _match_pattern(noise)
+        assert find is None, f"pattern must not match: {noise}"
+
+
+def test_every_pattern_is_anchored_to_filterbyproviders():
+    # Guards against a future pattern broad enough to rewrite arbitrary JS.
+    for find, _replace in _PATTERNS:
+        assert "filterByProviders" in find.pattern
+
+
+def test_patterns_compile_and_replacements_reference_group_one():
+    for find, replace in _PATTERNS:
+        assert isinstance(find, re.Pattern)
+        assert r"\1" in replace, "replacement must preserve the binding name"