Python: fix(ag-ui): dedupe client-replayed transcripts on resume

[LI (ktz03)]

Summary

• On non-use_service_session AG-UI resume, seed history via _reconstruct_messages_from_thread_snapshot instead of naive concatenation.
• Apply the same reconstructor for workflow resume/checkpoint builder seeding when a stored snapshot exists.
• Add a focused regression test for replayed-transcript vs interrupt-only resume shapes.

Fixes #8140

Test plan

• Unit: replayed transcript on resume does not duplicate message ids
• Unit: interrupt-only resume still prepends stored history
• Existing AG-UI HITL / snapshot tests remain green

[Copilot]

🟡 Changes recommended

Empty-message resumes can lose stored history in both agent and workflow paths.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Updates AG-UI resume handling to deduplicate client-replayed transcripts using snapshot reconstruction.

Changes:

• Applies reconstruction to agent and workflow resume history.
• Adds transcript deduplication regression tests.

File summaries

File	Review
python/packages/ag-ui/tests/ag_ui/test_resume_transcript_dedupe.py	Adds tests, but misses empty-message integration coverage and the required copyright header.
python/packages/ag-ui/agent_framework_ag_ui/_workflow.py	Reconstruction drops stored history for empty checkpoint-resume input.
python/packages/ag-ui/agent_framework_ag_ui/_agent_run.py	Reconstruction drops stored history for empty approval-resume input.

Review details

Suppressed comments (1)

python/packages/ag-ui/tests/ag_ui/test_resume_transcript_dedupe.py:1

• This new Python file is missing the required first-line copyright header mandated by python/CODING_STANDARD.md:453 and used throughout this test directory.

"""Regression for AG-UI resume with client-replayed transcript (#8140)."""

• Files reviewed: 3/3 changed files
• Comments generated: 3
• Review effort level: Balanced

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[LI (ktz03)]

@microsoft-github-policy-service agree

[LI (ktz03)]

Addressed Copilot review:

1. Empty messages on resume — agent (_agent_run) and workflow (_workflow) now use _reconstruct_messages_from_thread_snapshot only when the client sent a non-empty transcript; empty approval/checkpoint resumes still go through resume_seeded_messages so stored history is kept.
2. Tests — added the required copyright header, documented the empty-input reconstructor contract, and clarified the partial-turn case.

Existing test_endpoint / test_workflow_agent empty-resume assertions should stay green with this branching.

[LI (ktz03)]

Addressed on head 3bb98c18:

• Empty messages on approval/checkpoint resume again goes through resume_seeded_messages (agent + workflow), so stored history is preserved.
• Non-empty / client-replayed transcripts still use _reconstruct_messages_from_thread_snapshot for dedupe.
• Added a unit test documenting the reconstructor’s empty-input contract ([] unchanged → call sites must seed).

Existing test_endpoint / test_workflow_agent empty-resume assertions should stay green with this branching. Please re-run Copilot review on the latest head when convenient.

[LI (ktz03)]

Thanks Evan Mattson (@moonbox3) — addressed both points on this head:

1. ThreadSnapshotSession.reconcile_resume_messages now owns the empty-vs-nonempty resume decision (empty → resume_seeded_messages, non-empty → overlap reconstructor). Agent approval resume and workflow resume/checkpoint seeding both call this single method.
2. Generic non-service resumes (resume_payload without approval-interrupt ids) also go through reconcile and set seeded_resume_from_snapshot = True, so save-time resume_seeded_messages no longer double-prepends after a client-replayed transcript.

Added a unit test covering the session-owned empty vs replayed shapes.

[Evan Mattson (moonbox3)]

Please resolve individual comments with a note if addressed or not. Then resolve when complete.

[LI (ktz03)]

Evan Mattson (@moonbox3) Done — replied on each review thread with addressed/partial notes and resolved all five threads. Please take another look when convenient.