Fix 1767 (#1769)

* add branch audit file

* Fix NVX runtime detection to check actual CFFI modules

Problem:
When installing from source with AUTOBAHN_USE_NVX=0 (no NVX build), the
runtime detection incorrectly reported HAS_NVX=True, causing crashes when
attempting to use NVX functionality.

Root Cause:
The detection was importing Python wrapper modules (autobahn.nvx._xormasker
and autobahn.nvx._utf8validator) which are always importable as they're
Python files. The actual CFFI extension modules (_nvx_xormasker and
_nvx_utf8validator) are only imported lazily inside the wrapper classes'
__init__ methods, so their availability wasn't being checked.

Solution:
Changed detection to directly import the CFFI extension modules:
- import _nvx_utf8validator
- import _nvx_xormasker

This correctly detects whether NVX was actually built at install time:
- If NVX was built: CFFI modules exist → HAS_NVX=True
- If NVX wasn't built: CFFI modules don't exist → ImportError → HAS_NVX=False

Testing:
- With CFFI modules available: HAS_NVX=True, USES_NVX=True ✓
- With CFFI modules blocked: HAS_NVX=False, USES_NVX=False ✓

This ensures the pure Python fallback is correctly used when NVX isn't built.

Fixes #1767

Note: This work was completed with AI assistance (Claude Code).

Author: oberstet

.audit/oberstet_fix_1767.md

@@ -0,0 +1,8 @@
+- [ ] I did **not** use any AI-assistance tools to help create this pull request.
+- [x] I **did** use AI-assistance tools to *help* create this pull request.
+- [x] I have read, understood and followed the projects' [AI Policy](https://github.com/crossbario/autobahn-python/blob/main/AI_POLICY.md) when creating code, documentation etc. for this pull request.
+
+Submitted by: @oberstet
+Date: 2025-11-21
+Related issue(s): #1767
+Branch: oberstet:fix_1767

autobahn/websocket/__init__.py

@@ -43,9 +43,11 @@
 # Step 1: Probe for NVX availability (was it built and can we import it?)
 _has_nvx = False
 try:
-    # Try importing both NVX modules to verify they're available
-    from autobahn.nvx._xormasker import create_xor_masker as _nvx_xor_test  # noqa: F401
-    from autobahn.nvx._utf8validator import Utf8Validator as _nvx_utf8_test  # noqa: F401
+    # Try importing the actual CFFI extension modules directly
+    # (not just the Python wrappers which are always importable)
+    # This correctly detects if NVX was actually built at install time
+    import _nvx_utf8validator  # noqa: F401
+    import _nvx_xormasker  # noqa: F401
 
     _has_nvx = True
 except ImportError: