Stop reporting a silent workflow as a completed task

n8n answers 200 with an empty body when a node throws before the Respond node
runs — a refused token exchange is the common way in. The adapter read that as
a completed task carrying "(the workflow returned nothing)", which tells the
caller the task succeeded: the one thing certainly false.

Off-contract replies get the same treatment. They are still returned raw so
drift is visible, but a body that is not the contract cannot be read as
agreement.

Also removes a backlog section that described the events as unbuilt and said an
event should carry sub and azp from the caller's token — the design the user
overruled. Anyone reading it would have built the wrong consumer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

adapter/tests/test_adapter.py

@@ -11,7 +11,7 @@ import httpx
 import pytest
 
 from a2a_n8n_adapter.config import Settings
-from a2a_n8n_adapter.server import _read, build_agent_card
+from a2a_n8n_adapter.server import Outcome, _read, build_agent_card
 
 
 def settings(**over) -> Settings:
@@ -35,27 +35,35 @@ def response(payload, status=200) -> httpx.Response:
 
 class TestReadingTheWorkflow:
     def test_the_contracted_shape(self) -> None:
-        assert _read(response({"answer": "yes", "escalate": False})) == ("yes", False)
+        assert _read(response({"answer": "yes", "escalate": False})) == ("yes", Outcome.ANSWERED)
 
     def test_n8n_wraps_its_last_node_in_an_array(self) -> None:
-        assert _read(response([{"answer": "yes"}])) == ("yes", False)
+        assert _read(response([{"answer": "yes"}])) == ("yes", Outcome.ANSWERED)
 
     def test_escalation_is_carried_not_swallowed(self) -> None:
         # An autonomous agent meeting a rule that needs approval must escalate.
         # Losing this flag would turn "a human must look" into "done".
         assert _read(response({"answer": "needs approval", "escalate": True})) == (
             "needs approval",
-            True,
+            Outcome.ESCALATED,
         )
 
     def test_an_off_contract_reply_is_returned_raw(self) -> None:
         # Visible rather than reinterpreted: a workflow that has drifted should
         # look wrong, not be quietly guessed at.
-        text, escalate = _read(response("plain text"))
-        assert text == "plain text" and escalate is False
+        # Off contract is not agreement. Returned raw so the drift is visible,
+        # but never as a completed answer.
+        text, outcome = _read(response("plain text"))
+        assert text == "plain text" and outcome is Outcome.OFF_CONTRACT
 
     def test_an_empty_reply_says_so(self) -> None:
-        assert _read(response("")) == ("(the workflow returned nothing)", False)
+        # HTTP 200 with an empty body is what n8n returns when a node throws
+        # before the reply is built — a refused token exchange, usually. Reading
+        # it as a completed answer told the caller the task succeeded, which was
+        # the one thing certainly false.
+        text, outcome = _read(response(""))
+        assert outcome is Outcome.SILENT
+        assert "no answer" in text
 
 
 class TestAgentCard: