chore(release): 4.2.1 — register extension.manager.supports_csrf_post feature flag (#2823)

Lets clients detect CSRF-POST backend support via ComfyUI core's feature_flags
instead of parsing version strings. Absence of the flag indicates a Manager
version < 4.2.1 that is incompatible with POST-only state-mutation endpoints.

Follow-up to #2818; no endpoint or security behavior change.

comfyui_manager/__init__.py

@@ -6,6 +6,26 @@ from .common import manager_security
 from comfy.cli_args import args
 
 
+# Register server-push feature flag so ComfyUI_frontend (and other clients)
+# can detect CSRF-POST backend capability as a semantic contract (vs version
+# string parsing). See PR #2818 for context; clients use this flag to decide
+# whether to invoke POST state-mutation endpoints. Manager versions prior to
+# 4.2.1 do not set this flag — clients should treat its absence as
+# 'incompatible with POST-only state-mutation endpoints'.
+try:
+    from comfy_api import feature_flags as _core_feature_flags
+    _mgr_flags = (
+        _core_feature_flags.SERVER_FEATURE_FLAGS
+        .setdefault('extension', {})
+        .setdefault('manager', {})
+    )
+    _mgr_flags['supports_csrf_post'] = True
+except ImportError:
+    # Older ComfyUI core without comfy_api.feature_flags module.
+    # Manager functions but clients will not observe the flag.
+    pass
+
+
 def prestartup():
     from . import prestartup_script  # noqa: F401
     logging.info('[PRE] ComfyUI-Manager')