Python: Add more specific exceptions to Workflow

[TaoChenOSU]

Motivation and Context

Addresses #695

Workflows have been using very generic exception types (RuntimeError or ValueError) and users must heavily rely on exception messages to distinguish different types of exceptions.

Description

This PR sets up a new _exceptions module for us to add more specific exceptions to Workflows.
This PR adds the following to start:

• WorkflowException
• WorkflowRunnerException
• WorkflowConvergenceException
• WorkflowCheckpointException

This PR also fixes a less obvious issue in the runner: the runner no longer resets the iteration counts after converging. Reset is purely driven externally now, via reset_iteration_count. This makes sure that if the workflow converges because it's waiting for responses for requests, the runner maintains its iteration count.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework/_workflows
_exceptions.py	9	0	100%
_runner.py	213	32	84%	124–125, 165–168, 172, 213–215, 240–241, 243, 278–280, 304–308, 312, 347, 351, 353, 359, 367–370, 383, 423
_runner_context.py	166	6	96%	78, 81, 377, 397, 485, 489
_workflow.py	247	17	93%	88, 258–260, 262–263, 281, 309, 410, 687, 721, 726, 729, 748–750, 815
TOTAL	16801	2520	85%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3031	207 💤	0 ❌	0 🔥	1m 4s ⏱️

[Copilot]

Pull request overview

This PR introduces a new exception hierarchy for workflows to replace generic RuntimeError and ValueError exceptions with more specific exception types. The changes enable users to catch and handle workflow-specific errors more precisely.

Changes:

• Added new _exceptions.py module with WorkflowException, WorkflowRunnerException, WorkflowConvergenceException, and WorkflowCheckpointException
• Updated _runner.py to use new exception types for convergence and checkpoint errors, and changed restore_from_checkpoint to raise exceptions instead of returning boolean
• Removed iteration count reset after convergence (preserves iteration count for inspection)
• Updated all related tests to expect the new exception types

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
python/packages/core/agent_framework/_workflows/_exceptions.py	New module defining the workflow exception hierarchy
python/packages/core/agent_framework/_workflows/_runner.py	Updated to use new exception types; changed restore_from_checkpoint to raise exceptions; removed iteration reset
python/packages/core/agent_framework/_workflows/_workflow.py	Simplified checkpoint restoration error handling by removing boolean check
python/packages/core/agent_framework/_workflows/__init__.py	Added exports for new exception types
python/packages/core/tests/workflow/test_workflow.py	Updated tests to expect WorkflowConvergenceException and WorkflowCheckpointException; formatting improvements
python/packages/core/tests/workflow/test_runner.py	Updated tests to expect new exception types; added test for iteration count preservation
python/packages/core/tests/workflow/test_magentic.py	Updated tests to expect WorkflowCheckpointException; formatting improvements
python/packages/core/tests/workflow/test_checkpoint_validation.py	Updated test to expect WorkflowCheckpointException