ACP in JetBrains Rider: assistant output chunks are delayed/truncated until next prompt when using GLM5 plugin

[nkosi23]

Summary

When using OpenCode via ACP in JetBrains Rider (confirmed with GLM5 plugin, possibly other plugins), assistant output is often not streamed fully in real time. Part of the response appears to be missing/truncated, and the missing content is only flushed/displayed when the next prompt is submitted.
Expected Behavior

Assistant output should stream continuously and completely during a single response, without requiring a follow-up prompt to reveal missing chunks.

Actual Behavior

• Initial response appears truncated or incomplete.
• Remaining output appears right before (or as part of UI handling for) the next prompt submission.
• This creates the perception that streaming stopped early.

Environment

- IDE: JetBrains Rider
- Integration: OpenCode ACP agent plugin
- Model/plugin: GLM5 plugin (possibly reproducible with others)
- Transport: ACP session streaming/events

Notes / Suspected Cause

This may be related to client handling of incremental events (e.g., message.part.delta vs message.part.updated) or buffering/flush behavior in plugin-side rendering. It appears some chunks are received but not rendered until a subsequent interaction triggers UI flush.

Impact

- Confusing UX (looks like model stopped early).
- Hard to trust completeness of responses.
- Slower workflow due to manual “poke” (next prompt) required to reveal missing text.

Request

Please investigate ACP event/chunk handling in JetBrains plugin integrations and ensure incremental chunks are flushed/rendered immediately, including fallback behavior when only updated events are emitted.

Plugins

OpenCode ACP agent integration in JetBrains Rider

OpenCode version

1.2.15

Steps to reproduce

1. Start OpenCode ACP agent integration in JetBrains Rider.
2. Use GLM5 plugin (or another plugin) for a response that streams multiple chunks.
3. Observe that output appears incomplete at end of generation.
4. Send a new prompt.
5. Notice previously missing output appears before the new request is actually sent upstream.

Screenshot and/or share link

Operating System

OpenSUSE Tumbleweed

Terminal

No response

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• ACP: premature tool_call_update with in_progress clobbers pending session/request_permission dialog #14301: ACP premature tool_call_update event handling — also an ACP streaming/event-ordering bug that may share root cause
• Agent response not visible to user despite responding correctly #11512: Agent response not visible to user despite responding correctly — similar symptom where output is generated but not displayed to the client in real time