Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

Does onPostToolUse hook additionalContext get injected into sub-agent context?

Open
#1,971 0 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Documentation
Clarity
Needs clarification
Activity status
Quiet
Tech stack
javascript
Domain
api, developer-experience

Research direction

Start with the onPostToolUse hook, task tool, and session.send({ mode: "immediate" }) entry points using the listed SDK versions. Reproduce the behavior while checking the session journal for hook.start and hook.end events and the sub-agent's received context. Done means the context scope, message delivery behavior, and recommended mid-turn steering method are clearly documented.

Written by the indexing model from the issue text.

Description

question

Context

We're building a qa agent. It has an orchestrator agent that dispatches work to custom sub-agents via the task tool. We use session-level onPostToolUse hooks to enforce guardrails (retry limits on failing tests). The hooks fire correctly during sub-agent execution — we can see hook.start/hook.end events in the session journal, and onPreToolUse denials work as expected inside sub-agents.

What we observe

We have a guardrail that tracks test failures per spec. After 3 failures, we want to tell the sub-agent "stop retrying, mark as fixme, move on." Currently our hook calls session.send({ prompt: text, mode: "immediate" }) separately. The sub-agent ignores this and keeps retrying (7+ attempts observed).

Before max attempts, we return { additionalContext: feedbackText } from the hook (per-attempt guidance like "attempt 2/3, try a different approach"). We haven't been able to confirm whether this feedback actually reaches the sub-agent.

Questions

  1. Does { additionalContext } returned from onPostToolUse get injected into the active sub-agent's context, or only the parent session?
  2. Does session.send({ mode: "immediate" }) reach a running sub-agent, or does it queue on the parent session?
  3. What is the recommended way to steer a sub-agent mid-turn from a hook?

Environment

  • @github/copilot-sdk@1.0.6
  • @github/copilot@1.0.70
  • Custom agents with tools: null (all tools)
  • Hooks registered at session creation via hooks: { onPreToolUse, onPostToolUse }
Dominant language
Java
Stars
10.5k
Forks
1.5k
Avg merge
1d 9h
Merged PRs (30d)
131

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from github/copilot-sdk

All issues in github/copilot-sdk

Similar issues

More Java issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.