Visibility bump: #3984 / #3991 (AgentTool event streaming propagation) — status update requested

[mattmcc-attest]

Filing to bump visibility on the long-running thread around AgentTool event streaming.

• Issue: #3984 — "Feature Request: Support Event Streaming propagation from AgentTool (Sub-agents) to Runner". Opened 2025-12-20, 15 ❤️ reactions on the original post, last maintainer comment 2026-02-11 ("currently under review").
• PR: #3991 — "feat(agent-tool): Add event streaming propagation from AgentTool sub-agents to Runner". Opened 2025-12-21 by @sarojrout, 18 commits, 36 PR-conversation comments, 28 review comments. Last update 2026-05-15. Currently in a dirty merge state.

The problem (one sentence): when a sub-agent is wrapped as AgentTool, its events (function_call, function_response, partial-text, per-tool thinking) are consumed inside AgentTool.run_async — only the final merged text returns to the parent Runner. That makes long-running sub-agents look unresponsive on the wire and blocks any kind of per-step UI feedback in real time.

Workarounds in the wild (visible across the comment threads on #3984 and #3991):

• asyncio.Queue + contextvars + a parallel transport that merges sub-agent events with the SSE stream (see @CS-PK's comment on #3984 for a production description).
• /run_sse route overrides re-implementing ADK's event serialisation.
• Background drain tasks bridging child Runners' events into the parent stream.

Each of these is a private re-implementation of what should be a first-class feature, and each mirrors ADK internals — so each is fragile to internal changes between releases.

Asks:

1. Status update from the ADK team — is feat(agent-tool): Add event streaming propagation from AgentTool sub-agents to Runner #3991's approach (run_async_with_events() + dispatcher change in functions.py) the intended direction, or is a different design in flight?
2. Design feedback on feat(agent-tool): Add event streaming propagation from AgentTool sub-agents to Runner #3991 — the PR has had several rounds of community review/revisions and the author is responsive. If there's blocking feedback, a single round-trip from a maintainer would likely unstick it.
3. Label / triage signal — Feature Request: Support Event Streaming propagation from AgentTool (Sub-agents) to Runner #3984 is still on needs review 5+ months after acknowledgement. Even moving it to a clearer state (accepted, proposed design needed, etc.) would help the community know whether to keep polishing feat(agent-tool): Add event streaming propagation from AgentTool sub-agents to Runner #3991 or wait.

Two reaction counts that suggest this matters to a lot of teams: 15 ❤️ on #3984's OP, 36 comments on #3991 from across the community. A short status note would go a long way.

Thanks for considering 🙏