Additional agent DAG tests (#750)

- test_agent_provenance.py: test_session_parent_uri,
  test_session_no_parent_uri, and 6 synthesis tests (types,
  single/multiple parents, document, label)
- test_on_action_callback.py: 3 tests — fires before tool, skipped
  for Final, works when None
- test_callback_message_id.py: 7 tests — message_id on think/observe/
  answer callbacks (streaming + non-streaming) and
  send_final_response
- test_parse_chunk_message_id.py (5 tests) - _parse_chunk propagates
  message_id for thought, observation, answer; handles missing
  gracefully
- test_explainability_parsing.py (+1) -
  test_dispatches_analysis_with_tooluse - Analysis+ToolUse mixin still
  dispatches to Analysis
- test_explainability.py (+1) -
  test_observation_found_via_subtrace_synthesis
- chain walker follows from sub-trace Synthesis to find Observation
  and
  Conclusion in correct order
- test_agent_provenance.py (+8) - session parent_uri (2), synthesis
  single/multiple parents, types, document, label (6)

tests/unit/test_agent/test_callback_message_id.py

@@ -0,0 +1,122 @@
+"""
+Tests that streaming callbacks set message_id on AgentResponse.
+"""
+
+import pytest
+from unittest.mock import AsyncMock, MagicMock
+
+from trustgraph.agent.orchestrator.pattern_base import PatternBase
+from trustgraph.schema import AgentResponse
+
+
+@pytest.fixture
+def pattern():
+    processor = MagicMock()
+    return PatternBase(processor)
+
+
+class TestThinkCallbackMessageId:
+
+    @pytest.mark.asyncio
+    async def test_streaming_think_has_message_id(self, pattern):
+        responses = []
+        async def capture(r):
+            responses.append(r)
+
+        msg_id = "urn:trustgraph:agent:sess/i1/thought"
+        think = pattern.make_think_callback(capture, streaming=True, message_id=msg_id)
+        await think("hello", is_final=False)
+
+        assert len(responses) == 1
+        assert responses[0].message_id == msg_id
+        assert responses[0].chunk_type == "thought"
+
+    @pytest.mark.asyncio
+    async def test_non_streaming_think_has_message_id(self, pattern):
+        responses = []
+        async def capture(r):
+            responses.append(r)
+
+        msg_id = "urn:trustgraph:agent:sess/i1/thought"
+        think = pattern.make_think_callback(capture, streaming=False, message_id=msg_id)
+        await think("hello")
+
+        assert responses[0].message_id == msg_id
+        assert responses[0].end_of_message is True
+
+
+class TestObserveCallbackMessageId:
+
+    @pytest.mark.asyncio
+    async def test_streaming_observe_has_message_id(self, pattern):
+        responses = []
+        async def capture(r):
+            responses.append(r)
+
+        msg_id = "urn:trustgraph:agent:sess/i1/observation"
+        observe = pattern.make_observe_callback(capture, streaming=True, message_id=msg_id)
+        await observe("result", is_final=True)
+
+        assert responses[0].message_id == msg_id
+        assert responses[0].chunk_type == "observation"
+
+
+class TestAnswerCallbackMessageId:
+
+    @pytest.mark.asyncio
+    async def test_streaming_answer_has_message_id(self, pattern):
+        responses = []
+        async def capture(r):
+            responses.append(r)
+
+        msg_id = "urn:trustgraph:agent:sess/final"
+        answer = pattern.make_answer_callback(capture, streaming=True, message_id=msg_id)
+        await answer("the answer")
+
+        assert responses[0].message_id == msg_id
+        assert responses[0].chunk_type == "answer"
+
+    @pytest.mark.asyncio
+    async def test_no_message_id_default(self, pattern):
+        responses = []
+        async def capture(r):
+            responses.append(r)
+
+        answer = pattern.make_answer_callback(capture, streaming=True)
+        await answer("the answer")
+
+        assert responses[0].message_id == ""
+
+
+class TestSendFinalResponseMessageId:
+
+    @pytest.mark.asyncio
+    async def test_streaming_final_has_message_id(self, pattern):
+        responses = []
+        async def capture(r):
+            responses.append(r)
+
+        msg_id = "urn:trustgraph:agent:sess/final"
+        await pattern.send_final_response(
+            capture, streaming=True, answer_text="answer",
+            message_id=msg_id,
+        )
+
+        # Should get content chunk + end-of-dialog marker
+        assert all(r.message_id == msg_id for r in responses)
+
+    @pytest.mark.asyncio
+    async def test_non_streaming_final_has_message_id(self, pattern):
+        responses = []
+        async def capture(r):
+            responses.append(r)
+
+        msg_id = "urn:trustgraph:agent:sess/final"
+        await pattern.send_final_response(
+            capture, streaming=False, answer_text="answer",
+            message_id=msg_id,
+        )
+
+        assert len(responses) == 1
+        assert responses[0].message_id == msg_id
+        assert responses[0].end_of_dialog is True