* Fix handoff orchestration not passing user message to handoff target agent (#3161)
Filter out internal handoff function call and tool result messages before
passing conversation history to the target agent's LLM. These messages
confused the model into ignoring the original user question.
* Add handoff tool call filtering behavior and enhance workflow builder
- Introduced HandoffToolCallFilteringBehavior enum to specify filtering behavior for tool call contents in handoff workflows.
- Updated HandoffsWorkflowBuilder to support customizable handoff instructions and tool call filtering behavior.
- Enhanced HandoffAgentExecutor to utilize new filtering options for improved message handling during agent handoffs.
* Enhance handoff message filtering logic and add unit tests for filtering behaviors
* Refactor HandoffMessagesFilter to remove unused handoff function names and enhance filtering logic for non-handoff function calls
* Refactor HandoffMessagesFilter to streamline FilterCandidateState initialization and improve clarity
* Refactor HandoffMessagesFilter to improve filtering logic and add integration tests for handoff workflows
* fix: HandoffAgentExecutor tests
Remove input type checking in favour of explicit `.DescribeProtocolAsync()` flow. Also removes `.AsAgentAsync()` as the validation happens at workflow run time. This makes it easier to use Workflows with DI without resorting to async-over-sync.
* refactor: remove unused internals
* feat: Execution Mode for sharing a workflow among concurrent runs
* feat: Update WorkflowHostAgent to support concurrent execution
* Also update AsAgent APIs to support injecting a CheckpointManager and an IWorkflowExecutionEnvironment
* fix: Make Read logic consistent in DeclarativeWorkflowContext