Python: Fix missing methods on the Content class in durable tasks (#4738)

* Fix Content serialization in DurableAgentStateUnknownContent (#4719)

DurableAgentStateUnknownContent.from_unknown_content() stored raw Content
objects without converting them to dicts, causing json.dumps to fail in
Azure Durable Functions' entity state serialization. This affected content
types not explicitly handled (e.g., mcp_server_tool_call/result).

The fix converts Content objects to dicts via to_dict() when storing in
DurableAgentStateUnknownContent, and restores them via Content.from_dict()
in to_ai_content().

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add to_json and from_json methods to Content class (#4719)

Add to_json() and from_json() methods to the Content class to match the
serialization interface provided by SerializationMixin on other model classes.
Also fix pre-existing pyright type errors in durabletask's
DurableAgentStateUnknownContent.to_ai_content().

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address PR review: add type guard, remove to_json, add fallback, and tests

- Remove Content.to_json() per reviewer request (comment 3)
- Add type guard in Content.from_json() for non-dict JSON (comments 1, 4)
- Wrap json.JSONDecodeError as ValueError for consistent exception contract
- Add try/except fallback in to_ai_content() for invalid Content dicts (comment 5)
- Add test_content_to_dict_exclude_none and test_content_to_dict_exclude_fields (comment 2)
- Add test_unknown_content_to_ai_content_fallback_on_invalid_type_dict (comment 5)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Apply pre-commit auto-fixes

* Address review feedback for #4719: review comment fixes

* Remove Content.from_json, move logic to consuming code (#4719)

Remove the from_json convenience method from Content class per review
feedback. This is the same trivial json.loads + from_dict wrapper as
to_json which was already removed. Consumers should call json.loads
and Content.from_dict directly.

Update tests to use Content.from_dict(json.loads(...)) pattern and
remove from_json-specific error handling tests (those errors are
already covered by json.loads and Content.from_dict).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/durabletask/agent_framework_durabletask/_durable_agent_state.py

@@ -1318,9 +1318,17 @@ class DurableAgentStateUnknownContent(DurableAgentStateContent):
 
     @staticmethod
     def from_unknown_content(content: Any) -> DurableAgentStateUnknownContent:
+        if isinstance(content, Content):
+            return DurableAgentStateUnknownContent(content=content.to_dict())
         return DurableAgentStateUnknownContent(content=content)
 
     def to_ai_content(self) -> Content:
         if not self.content:
             raise Exception("The content is missing and cannot be converted to valid AI content.")
+        content_value: Any = self.content
+        if isinstance(content_value, dict) and "type" in content_value:
+            try:
+                return Content.from_dict(cast(dict[str, Any], content_value))
+            except (ValueError, TypeError):
+                pass
         return Content(type=self.type, additional_properties={"content": self.content})  # type: ignore

python/packages/durabletask/tests/test_durable_agent_state.py

@@ -2,16 +2,19 @@
 
 """Unit tests for DurableAgentState and related classes."""
 
+import json
 from datetime import datetime
 
 import pytest
-from agent_framework import UsageDetails
+from agent_framework import Content, Message, UsageDetails
 
 from agent_framework_durabletask._durable_agent_state import (
     DurableAgentState,
+    DurableAgentStateContent,
     DurableAgentStateMessage,
     DurableAgentStateRequest,
     DurableAgentStateTextContent,
+    DurableAgentStateUnknownContent,
     DurableAgentStateUsage,
 )
 from agent_framework_durabletask._models import RunRequest
@@ -373,5 +376,117 @@ class TestDurableAgentStateUsage:
         assert restored.get("total_token_count") == original.get("total_token_count")
 
 
+class TestDurableAgentStateUnknownContent:
+    """Test suite for DurableAgentStateUnknownContent serialization."""
+
+    def test_unknown_content_from_content_object_produces_serializable_dict(self) -> None:
+        """Test that from_unknown_content serializes Content objects to dicts."""
+        content = Content.from_mcp_server_tool_call(
+            call_id="call-1",
+            tool_name="search",
+            server_name="learn-mcp",
+            arguments={"query": "azure functions"},
+        )
+
+        unknown = DurableAgentStateUnknownContent.from_unknown_content(content)
+        result = unknown.to_dict()
+
+        # The content field should be a dict, not a Content object
+        assert isinstance(result["content"], dict)
+        assert result["content"]["type"] == "mcp_server_tool_call"
+
+    def test_unknown_content_to_dict_is_json_serializable(self) -> None:
+        """Test that to_dict output can be passed to json.dumps without error."""
+        content = Content.from_mcp_server_tool_result(
+            call_id="call-1",
+            output="Azure Functions documentation...",
+        )
+
+        unknown = DurableAgentStateUnknownContent.from_unknown_content(content)
+        result = unknown.to_dict()
+
+        # This must not raise TypeError
+        serialized = json.dumps(result)
+        assert serialized is not None
+
+    def test_unknown_content_round_trip_preserves_content(self) -> None:
+        """Test that Content objects survive serialization and deserialization."""
+        original = Content.from_mcp_server_tool_call(
+            call_id="call-1",
+            tool_name="fetch",
+            server_name="learn-mcp",
+            arguments={"url": "https://example.com"},
+        )
+
+        unknown = DurableAgentStateUnknownContent.from_unknown_content(original)
+        restored = unknown.to_ai_content()
+
+        assert restored.type == "mcp_server_tool_call"
+        assert restored.tool_name == "fetch"
+        assert restored.server_name == "learn-mcp"
+
+    def test_unknown_content_from_plain_dict_unchanged(self) -> None:
+        """Test that non-Content values are stored as-is."""
+        plain = {"some": "data"}
+
+        unknown = DurableAgentStateUnknownContent.from_unknown_content(plain)
+
+        assert unknown.content == {"some": "data"}
+
+    def test_unknown_content_to_ai_content_fallback_on_invalid_type_dict(self) -> None:
+        """Test that to_ai_content falls back when dict has 'type' but is not valid Content."""
+        invalid = {"type": "bogus_not_a_real_content_type", "extra": "stuff"}
+        unknown = DurableAgentStateUnknownContent(content=invalid)
+
+        result = unknown.to_ai_content()
+
+        assert result.type == "unknown"
+        assert result.additional_properties == {"content": invalid}
+
+    def test_from_ai_content_unknown_type_produces_serializable_state(self) -> None:
+        """Test that unknown content types in message conversion produce JSON-serializable state."""
+        content = Content.from_mcp_server_tool_call(
+            call_id="call-1",
+            tool_name="search",
+            server_name="learn-mcp",
+            arguments={"query": "create function app"},
+        )
+
+        durable_content = DurableAgentStateContent.from_ai_content(content)
+        data = durable_content.to_dict()
+
+        # Must be fully JSON-serializable
+        serialized = json.dumps(data)
+        assert serialized is not None
+
+    def test_state_with_mcp_content_is_json_serializable(self) -> None:
+        """Test that full DurableAgentState with MCP content can be serialized to JSON.
+
+        This reproduces the scenario from issue #4719 where agent state containing
+        MCP tool content could not be serialized by Azure Durable Functions.
+        """
+        state = DurableAgentState()
+        mcp_content = Content.from_mcp_server_tool_call(
+            call_id="call-1",
+            tool_name="search",
+            server_name="learn-mcp",
+            arguments={"query": "azure functions"},
+        )
+        message = DurableAgentStateMessage.from_chat_message(Message(role="assistant", contents=[mcp_content]))
+        state.data.conversation_history.append(
+            DurableAgentStateRequest(
+                correlation_id="test-mcp",
+                created_at=datetime.now(),
+                messages=[message],
+            )
+        )
+
+        state_dict = state.to_dict()
+
+        # This simulates what Azure Durable Functions does with entity state
+        serialized = json.dumps(state_dict)
+        assert serialized is not None
+
+
 if __name__ == "__main__":
     pytest.main([__file__, "-v", "--tb=short"])