fix(adapters): replace NodeInterrupt with FirewallBlocked exception

[Pranjal0410]

NodeInterrupt is deprecated in LangGraph V1. Worse - it doesn't actually raise. It returns {'__interrupt__': [...]} in the result dict and the graph keeps going. So the adapter's BLOCK decisions were silently becoming pauses. The attack text stayed in state.

Found this while writing examples for the adapter after PR #51 merged.

What changed

sdk/python/acf/models.py

• Added FirewallBlocked(FirewallError) - a proper exception that propagates out of invoke(). Callers catch it with normal try/except.

sdk/python/acf/adapters/langgraph.py

• Replaced NodeInterrupt with FirewallBlocked on BLOCK decisions. No more silent failures.
• Removed the langgraph.errors import entirely - adapter no longer depends on a deprecated API.

sdk/python/tests/adapters/test_langgraph.py

• Updated to test FirewallBlocked instead of NodeInterrupt. 22/22 passing. Full suite 110/110.

Why this matters

A firewall that reports BLOCK but doesn't actually stop the request is worse than no firewall. At least without a firewall you know you're unprotected. With the old behaviour you think you're safe and you're not.

Examples

Two runnable examples in examples/adapters/:

• langgraph_prompt_guard.py - clean prompt reaches the model, jailbreak gets stopped at the guard via FirewallBlocked
• langgraph_context_filter.py - 3 RAG chunks retrieved, one poisoned. Poisoned chunk filtered out, model runs on the clean two.

[tharindupr]

Few things to be fixed:

FirewallBlocked is not exported from the top-level acf package. acf/__init__.py exports FirewallError and FirewallConnectionError, but FirewallBlocked is missing from both the imports and __all__. It should be available via from acf import FirewallBlocked but right now that would raise ImportError. The example file works around this by using from acf.models import FirewallBlocked directly, which is why it wasn't caught.

The fix is two lines in __init__.py, add FirewallBlocked to the import and to __all__.

Two minor things also worth noting:

langgraph_prompt_guard.py has duplicate imports, from acf import Firewall and from acf.adapters.langgraph import FirewallNode each appear twice (lines 20–21 and 25–26).

[Pranjal0410]

both fixed @tharindupr. FirewallBlocked added to init.py exports and all. duplicate imports in the example cleaned up. 110/110 passing.