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feat: Support Sub-agent Escalation event in Parallel Agent#612

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jinnigu:feature/subagent-escalation
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feat: Support Sub-agent Escalation event in Parallel Agent#612
jinnigu wants to merge 1 commit intogoogle:mainfrom
jinnigu:feature/subagent-escalation

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@jinnigu jinnigu commented Nov 24, 2025

Fixes #561

Problem

ADK ParallelAgent did not support short-circuiting concurrent requests when a sub-agent sent a termination signal via an escalation event.

Changes

Modified ParallelAgent.java to use .takeUntil() on the merged event stream, listening for events with the escalate flag.
Added ParallelAgentEscalationTest.java to verify the escalation event triggers termination of other sub-agents.

Testing

  • ParallelAgentEscalationTest passes (verifies short-circuit behavior).
  • ParallelAgentTest passes (no regressions for normal parallel execution).
  • Verified that when one sub-agent escalates, other long-running sub-agents are cancelled immediately.

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gemini-code-assist bot commented Nov 24, 2025

Summary of Changes

Hello @jinnigu, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical limitation in the ADK ParallelAgent where it previously lacked the ability to terminate concurrent sub-agent operations upon receiving an escalation signal. The changes introduce a reactive mechanism to immediately halt all ongoing sub-agent activities when one sub-agent indicates an escalation, thereby improving efficiency and responsiveness by preventing redundant work.

Highlights

  • Sub-agent Escalation Support: The ParallelAgent now supports short-circuiting its execution when any of its sub-agents emit an event with an escalate flag set to true. This prevents unnecessary processing by other sub-agents once a critical event occurs.
  • New Test Coverage: A new test file, ParallelAgentEscalationTest.java, has been added to specifically verify the correct behavior of the ParallelAgent when an escalation event is triggered, ensuring that other sub-agents are terminated as expected.
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gemini-code-assist bot reviewed Nov 24, 2025
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Code Review

This pull request correctly implements the short-circuiting logic for escalation events in ParallelAgent by using the RxJava takeUntil operator. The accompanying new test, ParallelAgentEscalationTest, effectively validates this new behavior. However, I've identified a critical compilation issue in the test code due to a missing builder method, and a couple of medium-severity suggestions to improve code clarity and robustness in the test implementation.

@jinnigu jinnigu force-pushed the feature/subagent-escalation branch 4 times, most recently from 52e282e to 4677aba Compare November 24, 2025 07:42
@jinnigu jinnigu force-pushed the feature/subagent-escalation branch 2 times, most recently from 13645cf to 7fcf524 Compare March 28, 2026 05:25
tilgalas
tilgalas reviewed Mar 31, 2026
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core/src/test/java/com/google/adk/agents/ParallelAgentEscalationTest.java Outdated
}
}

static class SlowAgent extends BaseAgent {
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@tilgalas tilgalas Mar 31, 2026

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maybe we could merge the Escalating and Slow agents into a single TestAgent class, I feel like the code only differs in how the Event is constructed in the runAsyncImpl - this could be specified via constructor params for example, wdyt?

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@jinnigu jinnigu Apr 1, 2026

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Yes, merged into a single TestAgent class

tilgalas
tilgalas reviewed Mar 31, 2026
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core/src/test/java/com/google/adk/agents/ParallelAgentEscalationTest.java Outdated
public void runAsync_escalationEvent_shortCircuitsOtherAgents() {
TestScheduler testScheduler = new TestScheduler();

EscalatingAgent agent1 = new EscalatingAgent("agent1", 100, testScheduler);
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@tilgalas tilgalas Mar 31, 2026

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can we add another SlowAgent here (which would actually be a fast one) with a delay of say 50 (so that it's completed before the escalation happens) - I wanted to make sure that the EscalatingAgent escalation still preserves the events that happend prior to it completing

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@jinnigu jinnigu Apr 1, 2026

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Added a third agent to complete before escalation.

@jinnigu jinnigu force-pushed the feature/subagent-escalation branch from 7fcf524 to 88c8b0e Compare April 1, 2026 07:02
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Support Sub-agent Escalation event in Parallel Agent

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