fix(tui): batch streaming delta updates to prevent scroll freeze

[umi008]

Summary

• Each SSE delta triggered a full store mutation + re-render, causing UI freeze during rapid streaming
• Added 16ms buffer with Solid's batch() so rapid delta bursts coalesce into a single render cycle
• Three handlers wrapped: session.text.delta, session.tool.input.delta, session.reasoning.delta
• Final delta is always flushed via onCleanup to prevent lost trailing content
• Fixes TUI scroll freezes for seconds during fast-streaming responses (message.part.delta applied per-chunk with no batching) #36043

Testing

• tsgo --noEmit passes from packages/tui
• Manual: streaming is smooth without scroll jumps or freezes

Checklist

• Tested locally
• No unrelated changes
• Fixes TUI scroll freezes for seconds during fast-streaming responses (message.part.delta applied per-chunk with no batching) #36043

[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]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

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

Found a potential duplicate:

• PR fix(tui): batch streaming part deltas to keep TUI responsive during fast streams #36045: fix(tui): batch streaming part deltas to keep TUI responsive during fast streams
  • URL: fix(tui): batch streaming part deltas to keep TUI responsive during fast streams #36045
  • Related because: Both PRs address the same issue (TUI scroll freezes for seconds during fast-streaming responses (message.part.delta applied per-chunk with no batching) #36043) of UI freezing during rapid streaming updates in the TUI. PR fix(tui): batch streaming part deltas to keep TUI responsive during fast streams #36045 appears to be a similar approach to batch streaming delta updates to improve responsiveness during fast streams.

This looks like it may be a duplicate of PR #36090 (the current PR) addressing the same problem with the same solution approach.

[umi008]

Closing — duplicate of existing PR #36045 which addresses the same streaming delta batching.