Python: Finalize abandoned functional workflow streams without ContextVar leaks

[Shivani . (Shivani767)]

Motivation & Context

Abandoning a functional-workflow ResponseStream mid-iteration (async for event in stream: break) is a normal HITL pattern, but the run generator held both the OpenTelemetry run span and _framework_event_origin() open across yield. Garbage-collecting the generator later injects GeneratorExit from a different Context, so ContextVar.reset raises (Failed to detach context, async generator ignored GeneratorExit).

Description & Review Guide

• What are the major changes? Functional _run_core now starts the run span unattached (start_workflow_span) and activates it only around _execute. Framework lifecycle events are built inside _framework_event() so the origin token is reset before each yield. _framework_event_origin() also suppresses cross-context reset failures as a last line of defense.
• What is the impact of these changes? Breaking out of a streaming functional run no longer leaks loop exceptions. Event origin remains FRAMEWORK. Nested processing spans still parent under the run span during _execute. Graph Workflow._run_core is unchanged (same class of OTel attach-across-yield; can be a follow-up).
• What do you want reviewers to focus on? That we never yield while a ContextVar token is held, and that _activate_span around _execute is enough for nested-span parenting without reintroducing the leak.

Related Issue

Fixes #7787

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull request overview

Prevents ContextVar leaks when functional workflow streams are abandoned.

Changes:

• Uses unattached workflow spans with scoped activation.
• Builds framework events before yielding.
• Adds abandonment and span behavior tests.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
_functional.py	Revises functional workflow tracing and event emission.
_events.py	Adds safe framework-event construction.
observability.py	Adds unattached workflow span creation.
test_functional_workflow.py	Adds stream-abandonment regression tests.
test_observability.py	Tests unattached span behavior.

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[Evan Mattson (moonbox3)]

Thanks for taking care of this.

[Evan Mattson (moonbox3)]

Shivani . (@Shivani767) please fix the failing CI/CD checks

[github-actions]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
observability.py	1042	79	92%	448, 450–451, 454, 457, 460–461, 466–467, 473–474, 480–481, 488, 490–491, 494, 497, 500–501, 506–507, 513–514, 520–521, 528, 705–706, 916, 920–922, 924, 932–933, 937, 981, 983, 994–996, 998–1000, 1004, 1012, 1136–1137, 1372, 1659–1660, 1923, 1966–1967, 2156, 2397–2398, 2402, 2442–2443, 2447, 2488–2491, 2532–2533, 2684, 2687, 2699, 2716, 2720–2721, 2724, 2730, 2850, 3102, 3104
packages/core/agent_framework/_workflows
_events.py	156	13	91%	112–113, 261, 265, 267, 299, 381, 396, 411, 426, 439, 464, 470
_functional.py	498	29	94%	406–407, 473, 496, 505–507, 510, 540, 766–767, 774, 1043, 1076, 1079, 1087–1088, 1164–1165, 1171, 1562–1563, 1565, 1572–1575, 1596, 1621
TOTAL	47241	4362	90%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
9615	36 💤	0 ❌	0 🔥	2m 35s ⏱️

[Shivani . (Shivani767)]

Thanks for the review and for flagging the CI failures, Evan Mattson (@moonbox3).

I've pushed follow-up fixes to address the failing checks and the Copilot review feedback:

CI / typing

• Fixed pyright reportUnusedFunction on _framework_event / _framework_event_origin in _events.py
• Added the standard span-attribute subscript suppressions in test_start_workflow_span_does_not_attach_as_current

Copilot review follow-ups

• Reset the run guard in _run_core's finally so an abandoned stream no longer leaves _is_running = True and blocks a follow-up HITL run
• Extended the abandonment regression test to assert no OpenTelemetry detach errors and to verify a follow-up run succeeds after GC
• Added a functional-workflow observability test confirming nested processing spans parent under the workflow.run span

Unit tests were already passing; the blockers were the Package Checks and Test Typing Checks above.

Could you please approve and run workflows when you have a moment? The fork PR workflows are currently waiting on maintainer approval.

Branch: fix/7787-abandoned-functional-stream on Shivani767/agent-framework