Python: [BREAKING] Redesign Python exception hierarchy (#4082)

* [BREAKING] Redesign Python exception hierarchy

Replace the flat ServiceException family with domain-scoped branches:
- AgentException (with InvalidAuth, InvalidRequest, InvalidResponse, ContentFilter)
- ChatClientException (same consistent suberrors)
- IntegrationException (same + InitializationError)
- WorkflowException (Runner, Convergence, Checkpoint, Validation, Action, Declarative)
- ContentError (AdditionItemMismatch)
- ToolException / ToolExecutionException (unchanged)
- MiddlewareException / MiddlewareTermination (unchanged)

Key changes:
- All Service* exceptions removed (ServiceException, ServiceInitializationError, etc.)
- AgentExecutionException split into AgentInvalidRequest/ResponseException
- AgentInvocationError removed, split into AgentInvalidRequest/ResponseException
- Workflow exceptions moved from _workflows/_exceptions.py into main exceptions.py
- _workflows/__init__.py emptied; main __init__.py imports directly from submodules
- Purview exceptions re-parented under IntegrationException hierarchy
- Init validation errors use built-in ValueError/TypeError instead of custom exceptions
- CODING_STANDARD.md updated with hierarchy design and rationale

Fixes microsoft/agent-framework#3410

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

* Clarify ToolException vs ToolExecutionException docstrings

ToolException: base class for all tool-related exceptions (preconditions,
connection/init failures).
ToolExecutionException: runtime call failures (tool call failed, reconnect
failed, MCP errors).

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

* Fix remaining stale imports from agent_framework._workflows

- azurefunctions: _context.py, _app.py, _serialization.py, test_func_utils.py
  used 'from agent_framework._workflows import X' which broke after
  emptying _workflows/__init__.py; changed to direct submodule imports
- azure-ai-search: test still referenced ServiceInitializationError;
  updated to ValueError to match production code

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

---------

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

python/packages/declarative/tests/test_graph_coverage.py

@@ -1851,9 +1851,10 @@ class TestAgentExternalLoopCoverage:
         assert request.agent_name == "TestAgent"
 
     async def test_agent_executor_agent_error_handling(self, mock_context, mock_state):
-        """Test agent executor raises AgentInvocationError on failure."""
+        """Test agent executor raises AgentInvalidResponseException on failure."""
+        from agent_framework.exceptions import AgentInvalidResponseException
+
         from agent_framework_declarative._workflows._executors_agents import (
-            AgentInvocationError,
             InvokeAzureAgentExecutor,
         )
 
@@ -1871,7 +1872,7 @@ class TestAgentExternalLoopCoverage:
         }
         executor = InvokeAzureAgentExecutor(action_def, agents={"TestAgent": mock_agent})
 
-        with pytest.raises(AgentInvocationError) as exc_info:
+        with pytest.raises(AgentInvalidResponseException) as exc_info:
             await executor.handle_action(ActionTrigger(), mock_context)
 
         assert "TestAgent" in str(exc_info.value)
@@ -2375,11 +2376,12 @@ class TestAgentExecutorExternalLoop:
 
     async def test_handle_external_input_response_agent_not_found(self, mock_context, mock_state):
         """Test handling external input raises error when agent not found during resumption."""
+        from agent_framework.exceptions import AgentInvalidRequestException
+
         from agent_framework_declarative._workflows._executors_agents import (
             EXTERNAL_LOOP_STATE_KEY,
             AgentExternalInputRequest,
             AgentExternalInputResponse,
-            AgentInvocationError,
             ExternalLoopState,
             InvokeAzureAgentExecutor,
         )
@@ -2411,7 +2413,7 @@ class TestAgentExecutorExternalLoop:
         )
         response = AgentExternalInputResponse(user_input="continue")
 
-        with pytest.raises(AgentInvocationError) as exc_info:
+        with pytest.raises(AgentInvalidRequestException) as exc_info:
             await executor.handle_external_input_response(original_request, response, mock_context)
 
         assert "NonExistentAgent" in str(exc_info.value)

python/packages/declarative/tests/test_graph_executors.py

@@ -415,8 +415,9 @@ class TestAgentExecutors:
     @pytest.mark.asyncio
     async def test_invoke_agent_not_found(self, mock_context, mock_state):
         """Test InvokeAzureAgentExecutor raises error when agent not found."""
+        from agent_framework.exceptions import AgentInvalidRequestException
+
         from agent_framework_declarative._workflows import (
-            AgentInvocationError,
             InvokeAzureAgentExecutor,
         )
 
@@ -430,8 +431,8 @@ class TestAgentExecutors:
         }
         executor = InvokeAzureAgentExecutor(action_def)
 
-        # Execute - should raise AgentInvocationError
-        with pytest.raises(AgentInvocationError) as exc_info:
+        # Execute - should raise AgentInvalidRequestException
+        with pytest.raises(AgentInvalidRequestException) as exc_info:
             await executor.handle_action(ActionTrigger(), mock_context)
 
         assert "non_existent_agent" in str(exc_info.value)