[BREAKING] Python: Refactor workflow events to unified discriminated union pattern

[moonbox3]

Motivation and Context

• Replace individual event subclasses (ExecutorCompletedEvent, WorkflowOutputEvent, RequestInfoEvent, etc.) with a single generic WorkflowEvent[DataT] class using a type literal discriminator
• Use event.type == "output" pattern instead of isinstance(event, WorkflowOutputEvent) checks
• Align with [BREAKING] Python: Fix workflow as agent streaming output #3649 which removed AgentRunEvent/AgentRunUpdateEvent
• Removed exported event subclasses: ExecutorCompletedEvent, ExecutorFailedEvent, ExecutorInvokedEvent, RequestInfoEvent, SuperStepCompletedEvent, SuperStepStartedEvent, WorkflowFailedEvent, WorkflowLifecycleEvent, WorkflowOutputEvent, WorkflowStartedEvent, WorkflowStatusEvent
• Event type checking now uses event.type == "..." instead of isinstance()

Migration

# Before
if isinstance(event, WorkflowOutputEvent):
    process(event.data)

# After
if event.type == "output":
    process(event.data)

Description

• Closes Python: Use ExecutorEvent[T] generic to simplify event type hierarchy #3528
• Closes Python: Standardize __repr__ implementations across event classes #3547

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
_tools.py	789	85	89%	232, 278, 329, 331, 359, 529, 564–565, 667, 669, 689, 707, 721, 733, 738, 740, 747, 780, 851–853, 894, 916–944, 979, 987, 1228, 1433, 1490, 1494, 1573–1577, 1595, 1597–1598, 1703, 1707, 1757, 1759, 1775, 1777, 1841, 1868, 1921, 1989, 2168–2169, 2196, 2204, 2217, 2227–2228, 2263, 2319, 2351
packages/core/agent_framework/_workflows
_agent.py	349	66	81%	59, 67–73, 107–108, 349–350, 359–360, 367, 369, 375–376, 462–463, 472, 479, 505, 538–540, 542, 544, 546, 551, 556, 603, 633, 650, 689–692, 698, 704, 708–709, 712–718, 722–723, 729, 790, 797, 803–804, 815, 847, 854, 875, 884, 888, 890–892, 899
_agent_executor.py	166	22	86%	98, 146, 164–165, 216–217, 219–220, 252–254, 262–264, 274–276, 278, 282, 286, 290–291
_checkpoint.py	122	2	98%	186–187
_checkpoint_summary.py	27	4	85%	36–39
_edge.py	228	28	87%	46, 68–69, 71, 166, 196, 445–446, 451, 455–460, 462–464, 580, 694, 701–703, 750, 778, 804, 858, 872
_events.py	150	12	92%	91–92, 225, 229, 231, 263, 338, 353, 368, 383, 396, 411
_executor.py	176	12	93%	210, 334, 336, 345, 365, 368, 475, 480, 490, 649, 730–731
_runner.py	218	32	85%	132–133, 176–179, 183, 224–226, 251–252, 254, 289–291, 315–319, 323, 358, 362, 364, 370, 378–381, 394, 430
_runner_context.py	172	7	95%	86, 89, 385, 405, 482, 495, 499
_workflow.py	273	19	93%	86, 264–266, 268–269, 287, 291, 319, 421, 639, 681, 686, 689, 708–710, 723, 791
_workflow_context.py	157	9	94%	57–58, 66, 70, 84, 160, 185, 296, 415
_workflow_executor.py	182	30	83%	94, 444, 468, 470, 478–479, 484, 486, 491, 493, 546, 574–580, 584–586, 594, 599, 610, 620, 624, 630, 634, 644, 648
packages/orchestrations/agent_framework_orchestrations
_base_group_chat_orchestrator.py	166	12	92%	109, 277, 292, 326–328, 332, 351, 412, 458–460
_concurrent.py	193	30	84%	52, 61–62, 70–71, 90–91, 96, 123, 128, 133–134, 140, 162, 172, 179, 347, 350, 378, 434, 446, 485, 487–488, 490, 502–503, 508, 530, 534
_group_chat.py	294	39	86%	173, 336, 343, 372, 383–384, 390, 395, 411, 438–443, 445, 478–481, 483, 488–492, 656, 661, 675, 756, 762, 808, 828, 903–904, 938, 957, 976, 986
_handoff.py	382	57	85%	104–105, 107, 136–137, 159–169, 171, 173, 175, 180, 280, 334, 359, 387, 395–396, 410, 461–462, 494, 541–543, 730, 737, 742, 829, 832, 841–844, 854, 859, 866, 872–875, 910, 915, 1112, 1115, 1123, 1141, 1148, 1223
_magentic.py	617	90	85%	67–76, 81, 85–96, 261, 272, 276, 296, 357, 366, 368, 410, 427, 436–437, 439–441, 443, 454, 596, 598, 638, 686, 722–724, 726, 734–737, 741–744, 805–808, 899, 905, 911, 953, 991, 1023, 1040, 1051, 1108–1109, 1113–1115, 1139, 1163–1164, 1177, 1193, 1215, 1263–1264, 1302–1303, 1462, 1471, 1474, 1479, 1875, 1930, 1945, 1974
_orchestration_state.py	29	5	82%	22, 30, 70, 87–88
_sequential.py	114	14	87%	74, 167, 185, 196, 202, 239, 241–242, 244, 256–257, 262, 284, 288
TOTAL	16583	2022	87%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3912	225 💤	0 ❌	0 🔥	1m 9s ⏱️

[Copilot]

Pull request overview

This PR refactors Python workflow events from individual event subclasses (like ExecutorCompletedEvent, WorkflowOutputEvent, RequestInfoEvent) to a unified discriminated union pattern using a single generic WorkflowEvent[DataT] class with a type literal discriminator. This aligns with PR #3649 and resolves issues #3528 and #3547.

Changes:

• Replaced event subclasses with WorkflowEvent[DataT] generic type
• Changed event type checking from isinstance(event, WorkflowOutputEvent) to event.type == "output"
• Updated all samples, tests, and documentation to use the new pattern
• Removed exported event subclasses from public API

Reviewed changes

Copilot reviewed 117 out of 118 changed files in this pull request and generated 15 comments.

Show a summary per file

File	Description
python/samples/**/*.py	Updated 50+ sample files to use event.type == pattern instead of isinstance()
python/packages/core/tests/**/*.py	Updated 20+ test files with new event checking pattern
python/packages/orchestrations/**/*.py	Updated orchestration builders and tests
python/packages/devui/**/*.py	Updated DevUI mapper to use event.type discriminator
python/packages/core/agent_framework/_workflows/*.py	Core workflow implementation updates

[moonbox3]

@TaoChenOSU, I need these changes in for some other work I am doing - so I don't get stuck fixing conflicts for a day again. Please note anything and we can fast follow in another PR. Thanks.