Delegation fixes

[enyst]

End-user friendly description of the problem this fixes or functionality that this introduces

• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below
  Fix agent delegation; use events for communication between parent and delegates.
  Fix the lockup when the model returns a message instead of a tool call.

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Give a summary of what the PR does, explaining any non-trivial design decisions

Delegation was broken after we made the agent loop rely exclusively on a controller-as-observer logic. This PR proposes to fix it in a simple way: by forwarding to the delegate

• refactor the current logic (of unsubscribing parent when delegate starts and vice versa): now ONLY the parent is subscribed and stays subscribed, and it forwards to the delegate when it has one
• should_step on both MessageActions from 'user' and 'agent', except when waiting for user input is explicitly set
• should_step on DelegateAction too, it will create a MessageAction to kickstart the delegate
• refactor ending conditions
• added integration tests for DelegatorAgent

Also:

• the delegate starts with a MessageAction
• and ends with a AgentDelegateObservation/ErrorObservation

The code is ready for review - or this logic of delegation.
(please ignore the print() stuff, will clean up later)

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Link of any specific issues this addresses
Fix #6162

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:3df4d30-nikolaik   --name openhands-app-3df4d30   docker.all-hands.dev/all-hands-ai/openhands:3df4d30

[enyst]

@openhands-agent Read the diff of this PR carefully. Understand what it tries to achieve. Then, we have two things to do:

1. The diff has added debug prints. We need them! And we need to enhance them:

• all events have an event.id, add it to the print() statements after the class name, like '({event.id})'

2. The unit tests in test_agent_controller.py are outdated and failing. Update them to the new behavior. Understand the difference in the context of the changes of this PR and fix them.

Important:
You don't need to test the rest. Just this test file.

[github-actions]

Hi! I started running the integration tests on your PR. You will receive a comment with the results shortly.

[github-actions]

Hi! I started running the integration tests on your PR. You will receive a comment with the results shortly.

[github-actions]

Trigger by: Pull Request (integration-test label on PR #6165)
Commit: f2dcc79
Integration Tests Report (Haiku)
Haiku LLM Test Results:
Success rate: 100.00% (6/6)

Total cost: USD 0.00

instance_id	success	reason	cost	error_message
t02_add_bash_hello	True		0
t06_github_pr_browsing	True		0
t03_jupyter_write_file	True		0
t01_fix_simple_typo	True		0
t05_simple_browsing	True		0
t04_git_staging	True		0

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Integration Tests Report (DeepSeek)
DeepSeek LLM Test Results:
Success rate: 83.33% (5/6)

Total cost: USD 0.00

instance_id	success	reason	cost	error_message
t02_add_bash_hello	True		0
t03_jupyter_write_file	True		0
t04_git_staging	True		0
t01_fix_simple_typo	True		0
t06_github_pr_browsing	True		0
t05_simple_browsing	False	The answer is not found in any message. Total messages: 2.	0

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Integration Tests Report Delegator (Haiku)
Success rate: 50.00% (1/2)

Total cost: USD 0.00

instance_id	success	reason	cost	error_message
t02_add_bash_hello	True		0	nan
t01_fix_simple_typo	False	File not fixed: This is a silly typo.	0	RuntimeError: Agent reached maximum iteration in headless mode. Current iteration: 30, max iteration: 30
		Really!
		No more typos.
		Enjoy!

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Integration Tests Report Delegator (DeepSeek)
Success rate: 100.00% (2/2)

Total cost: USD 0.00

instance_id	success	reason	cost	error_message
t02_add_bash_hello	True		0
t01_fix_simple_typo	True		0

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Download testing outputs (includes both Haiku and DeepSeek results): Download

[diwu-sf]

Thanks!