feat(web): Show subagents under parent session, allow intuitive navigation between.

[jmagder]

What does this PR do?

Closes #14040

This PR improves the opencode web client by adding support for navigation between sessions and their subgents, through an intuitive UX:

You can watch a video demo here:

2026-02-17.17-31-40.mp4

In short:

• subagents are now shown as a tree under their parent session.
• The session can be collapsed.
• You can navigate to parent session or subagent through the sidebar navigation
• Subagent threads now have an icon in top right to show they are subagents
• Subagent threads can now navigate directly to their parent.

How did you verify your code works?

Aside from extensive testing, I added unit and e2e test for the feature. I also put together the video above demoing the feature.

The actual code changes are a few hundred lines. The tests take up 70% of the code, but if you are short on time less focus is needed on the *.spec.ts files.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found several related PRs that address subagent navigation features:

Potentially Related PRs:

1. feat: add subagents sidebar with clickable navigation and parent keybind #4865 - "feat: add subagents sidebar with clickable navigation and parent keybind"

   • feat: add subagents sidebar with clickable navigation and parent keybind #4865
   • Directly related: Implements sidebar navigation for subagents with parent navigation capability

2. feat: add interactive session switcher for subagent navigation #6184 - "feat: add interactive session switcher for subagent navigation"

   • feat: add interactive session switcher for subagent navigation #6184
   • Related: Provides session switching functionality for subagent navigation

3. feat(task): Add subagent-to-subagent delegation with budgets, persistent sessions, and hierarchical session navigation #7756 - "feat(task): Add subagent-to-subagent delegation with budgets, persistent sessions, and hierarchical session navigation"

   • feat(task): Add subagent-to-subagent delegation with budgets, persistent sessions, and hierarchical session navigation #7756
   • Related: Includes hierarchical session navigation for subagents

4. Add session position indicator in header and refactor sibling logic #5309 - "Add session position indicator in header and refactor sibling logic"

   • Add session position indicator in header and refactor sibling logic #5309
   • Potentially related: Session positioning and navigation logic

These PRs appear to address similar or overlapping features around subagent navigation and hierarchical session display. You may want to review them to ensure #14043 doesn't duplicate existing functionality.

[Cellule]

👍 on this feature!

[maddestructor]

Same, I'm all hyped for this feature! 👍

[nfreger-maintainX]

Can't wait!

[auryn-macmillan]

would love to see some version of this

[jmagder]

Appreciate the interest but I made this 5 months ago along with two other patches with heavy interest but I could not get anyone to review them and the other two were automatically closed. I love the project but I code day and night as a 20+ year startup veteran and don't want to waste time fixing merge conflicts that won't be reviewed. If anyone knows how to get the attention of the developers (three were requested to review) I'll reconsider but I've since given up on the project and started exploring other tooling instead.