Python: feat(ag-ui): add emit_messages_snapshot config to suppress terminal snapshot

[Manideep Malyala (manideep-malyala)]

Fixes #7807

Summary

Adds a new emit_messages_snapshot flag (defaulting to True) to AgentConfig in the agent_framework_ag_ui package.

When set to False, the terminal MessagesSnapshotEvent is suppressed at the end of the run. This allows clients using HistoryProvider (or those managing their own state) to avoid full transcript rewrites on the client side, while maintaining full backward compatibility for existing applications.

Changes Made

• Added emit_messages_snapshot boolean to AgentConfig
• Updated run_agent_stream logic to check this config before yielding _build_messages_snapshot(flow, snapshot_messages)
• Added a new test test_run_agent_stream_suppresses_messages_snapshot_if_configured in test_run.py to verify the suppression behavior.

[Copilot]

Pull request overview

Adds an opt-out for terminal message snapshots while preserving existing behavior by default.

Changes:

• Adds emit_messages_snapshot configuration.
• Conditionally suppresses terminal snapshots.
• Adds suppression coverage.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
_agent.py	Defines and propagates the configuration flag.
_agent_run.py	Applies the flag before emitting the snapshot.
test_run.py	Tests snapshot suppression and normal completion.

Suppressed comments (1)

python/packages/ag-ui/tests/ag_ui/test_run.py:1853

• Remove the trailing spaces on this blank line; Ruff formatting will reject whitespace-only blank lines.

---

💡 Add a code-review agent skill for context-aware, tailored reviews. Learn more in the docs.