feat(ui): Show subagent logs in bounded vertical view

[TheodoreSpeaks]

Summary

Subagent output can get pretty in the weeds and the user doesn't need to see all that. Like thinking, we should only display the last few lines to reduce visual noise. Note subagent thinking now renders as plaintext to avoid nested boxes in boxes.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• Other: ___________

Testing

• Validated locally, tested scrolling, refreshes, aborts.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

Screenshots/Videos

Screen.Recording.2026-04-23.at.2.38.29.PM.mov

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Apr 23, 2026 10:08pm

[TheodoreSpeaks]

@BugBot review

[cursor]

PR Summary

Medium Risk
Moderate UI behavior change in the chat transcript: subagent thinking/text is collapsed into a scrollable viewport with custom auto-stick-to-bottom logic, which could introduce scroll/overflow regressions while streaming.

Overview
Subagent output in agent groups is now displayed in a bounded, scrollable viewport (max height) with overflow fade indicators, reducing transcript noise.

Subagent thinking blocks are no longer rendered as nested ThinkingBlocks; subagent_text and subagent_thinking are both treated as plain text entries within the group.

While streaming, the viewport auto-sticks to bottom unless the user scrolls upward, using requestAnimationFrame-driven smooth scrolling and wheel/scroll listeners to detach/reattach.

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[greptile-apps]

Greptile Summary

This PR introduces a bounded scrollable viewport (BoundedViewport) for subagent logs in the agent group, capping height at 110 px with smooth RAF-driven auto-scroll and fade gradient overlays. It also flattens subagent thinking content to plain text (removing the nested ThinkingBlock) and fixes the abort handler to correctly tag stopped subagent blocks with lane: 'subagent' before persistence.

Confidence Score: 5/5

Safe to merge — changes are UI-only with no data-integrity risk and a correct abort-handler fix.

All three files contain well-scoped, internally consistent changes. The RAF loop is correctly cleaned up via useLayoutEffect's return value, the stickToBottom guard prevents infinite scroll races, and the overflow state update is guarded against spurious re-renders. The lane: 'subagent' addition is consistent with the existing pattern at line 712 and matches the stop-route schema.

No files require special attention.

Important Files Changed

Filename	Overview
apps/sim/app/workspace/[workspaceId]/home/components/message-content/components/agent-group/agent-group.tsx	Adds BoundedViewport component wrapping agent items in a 110px max-height scrollable container with RAF-based auto-scroll-to-bottom and fade gradients; removes the thinking AgentGroupItem variant in favour of rendering all subagent text/thinking as plain text.
apps/sim/app/workspace/[workspaceId]/home/components/message-content/message-content.tsx	Merges subagent_thinking block handling into the subagent_text branch so both are concatenated as plain text items; the dedicated thinking branch (with timing guards and ThinkingBlock rendering) is removed.
apps/sim/app/workspace/[workspaceId]/home/hooks/use-chat.ts	Adds lane: 'subagent' to serialized blocks in the stop/abort handler when block.subagent is set, so stopped subagent content is correctly tagged on persistence.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Stream Event Arrives] --> B{Block type?}
    B --> |subagent_text OR\nsubagent_thinking| C[Flatten to text item\nin AgentGroup]
    B --> |subagent_tool_call| D[ToolCallItem\nin AgentGroup]
    B --> |thinking| E[ThinkingBlock\nin main message]
    B --> |text| F[Plain text\nin main message]

    C --> G[AgentGroup renders\nBoundedViewport]
    D --> G
    G --> H{Content overflows\n110px?}
    H --> |Yes| I[Show top/bottom\ngradient fades]
    H --> |No| J[Render without fades]
    I --> K{isStreaming?}
    J --> K
    K --> |Yes + stickToBottom| L[RAF loop scrolls\nto bottom smoothly]
    K --> |No| M[Static view]

    subgraph Stop handler
    N[User stops stream] --> O[Map ContentBlock to\nstop API format]
    O --> P{block.subagent\ntruthy?}
    P --> |Yes| Q[Add lane: subagent]
    P --> |No| R[No lane field]
    end

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