Output stopps in the middle and only shown after next prompt (OpenCode w GPT 5.5)

[viblo]

What version of HAPI is running?

0.17.4

What platform is your computer?

Linux 6.12.0-16000.8-default x86_64 unknown

What issue are you seeing?

The (code in this case) output stops midway, and is only shown after I write a followup.

In the following screenshot I asked it to explain a thing, and it proceeded to list some options to fix it. However, the output stopped in the middle of Option 1. As soon as I wrote back (even just a "hi" like in this case), the missing output was shown. However, note that the formatting of the continuing output got broken, I guess because it was a code block that got split in half.

What steps can reproduce the bug?

It happens frequently, more or less with every long response.

What is the expected behavior?

That all the output is shown :)

Additional information

This was tried with OpenCode, using the Github Copilot GPT 5.5 model.

[github-actions]

Thanks for the report. I found a likely match in the OpenCode remote/ACP streaming path.

HAPI buffers ACP agentMessageChunk text and flushes it after session/prompt returns. After the prompt returns, HAPI waits for a short quiet period, flushes the buffered text, but keeps the same message handler alive. If OpenCode sends more session/update text after that flush, the text can remain buffered until the next prompt starts, because the next prompt explicitly flushes the previous handler before replacing it. That matches “missing output appears after I send another message”, and it can also split a markdown/code block across two rendered messages.

I also checked the local OpenCode path: local mode streams through the OpenCode plugin hook system, not this ACP prompt path.

Relevant code:

• cli/src/agent/backends/acp/AcpSdkBackend.ts:199 - OpenCode/Gemini ACP prompt entry point.
• cli/src/agent/backends/acp/AcpSdkBackend.ts:234 - waits for session updates to go quiet after session/prompt returns.
• cli/src/agent/backends/acp/AcpSdkBackend.ts:238 - flushes buffered assistant text.
• cli/src/agent/backends/acp/AcpSdkBackend.ts:331 - later session/update notifications still go to the existing handler.
• cli/src/agent/backends/acp/AcpSdkBackend.ts:213 - next prompt flushes the previous handler before creating a new one.
• cli/src/agent/backends/acp/AcpMessageHandler.ts:334 - agentMessageChunk text is buffered, not immediately emitted.
• cli/src/agent/backends/acp/AcpMessageHandler.ts:285 - flushText() emits the buffered text as one message.
• cli/README.md:35 - OpenCode supports both local and remote modes; local mode uses plugins.

Need more info:

• Was this session in local mode or remote/web-controlled mode when it happened?
• What OpenCode CLI version was running?
• If available, a DEBUG=1 HAPI log around one truncated turn.

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HAPI Bot