[lib] Fix threadPermissionsFromBitmaskHex invariant

Summary:
Really shouldn't have made this mistake...

After moving things around to resolve circular dependency issue, I accidentally started using the `tHexEncodedRolePermission` check in `threadPermissionsFromBitmaskHex` instead of the `tHexEncodedPermissionsBitmask` check...

This required that we have >=3 hex characters, when there's no such minimum for thread permissions.

Caught this during `native` testing thanks to thread where permissions for some user were "3", which should have been valid.

I read through `minimally-encoded-thread-permissions` again very carefully to see if there were any other mistakes I could find. I think part of the reason for the error may have been the similar-ish naming of all the utilities/etc. I'll see if I can update those to be more clear.

Also went ahead and included unit test that would've caught the issue earlier.

---

Depends on D10295

Test Plan: Unit test, careful re-reading of `threadPermissionsFromBitmaskHex`.

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10296

lib/permissions/minimally-encoded-thread-permissions.js

@@ -75,12 +75,12 @@ const permissionsToBitmaskHex = (
   return bitmask.toString(16);
 };
 
-const tHexEncodedRolePermission: TRegex = tRegex(/^[0-9a-fA-F]{3,}$/);
+const tHexEncodedPermissionsBitmask: TRegex = tRegex(/^[0-9a-fA-F]+$/);
 const threadPermissionsFromBitmaskHex = (
   permissionsBitmaskHex: string,
 ): ThreadPermissionsInfo => {
   invariant(
-    tHexEncodedRolePermission.is(permissionsBitmaskHex),
+    tHexEncodedPermissionsBitmask.is(permissionsBitmaskHex),
     'permissionsBitmaskHex must be valid hex string.',
   );
 
@@ -166,7 +166,7 @@ const inversePropagationPrefixes: Map<bigint, string> =
 const inverseFilterPrefixes: Map<bigint, string> =
   invertObjectToMap(filterPrefixes);
 
-const tHexEncodedPermissionsBitmask: TRegex = tRegex(/^[0-9a-fA-F]+$/);
+const tHexEncodedRolePermission: TRegex = tRegex(/^[0-9a-fA-F]{3,}$/);
 const decodeRolePermissionBitmask = (bitmask: string): string => {
   const bitmaskInt = BigInt(`0x${bitmask}`);
   const basePermission = (bitmaskInt >> BigInt(4)) & BigInt(63);

lib/permissions/minimally-encoded-thread-permissions.test.js

@@ -138,6 +138,38 @@ describe('threadPermissionsFromBitmaskHex', () => {
       expectedDecodedThreadPermissions,
     );
   });
+
+  it('should decode bitmask strings under 3 characters', () => {
+    // We know that '3' in hex is 0b0011. Given that permissions are encoded
+    // from least significant bit (LSB) to most significant bit (MSB), we would
+    // except this to mean that only the first two permissions listed in
+    // `baseRolePermissionEncoding` are `true`. Which is the case.
+    const decodedThreadPermissions = threadPermissionsFromBitmaskHex('3');
+    expect(decodedThreadPermissions).toStrictEqual({
+      know_of: { value: true, source: 'null' },
+      visible: { value: true, source: 'null' },
+      voiced: { value: false, source: null },
+      edit_entries: { value: false, source: null },
+      edit_thread: { value: false, source: null },
+      edit_thread_description: { value: false, source: null },
+      edit_thread_color: { value: false, source: null },
+      delete_thread: { value: false, source: null },
+      create_subthreads: { value: false, source: null },
+      create_sidebars: { value: false, source: null },
+      join_thread: { value: false, source: null },
+      edit_permissions: { value: false, source: null },
+      add_members: { value: false, source: null },
+      remove_members: { value: false, source: null },
+      change_role: { value: false, source: null },
+      leave_thread: { value: false, source: null },
+      react_to_message: { value: false, source: null },
+      edit_message: { value: false, source: null },
+      edit_thread_avatar: { value: false, source: null },
+      manage_pins: { value: false, source: null },
+      manage_invite_links: { value: false, source: null },
+      voiced_in_announcement_channels: { value: false, source: null },
+    });
+  });
 });
 
 describe('rolePermissionToBitmaskHex', () => {