opencode run --format json --session hangs after final answer is persisted #32506

Description

Summary

opencode run --format json --session <session_id> can hang even after the model has completed and the final assistant answer has been persisted to OpenCode’s session DB.

In our repro, the process stayed alive, stdout remained empty, but the SQLite session DB contained both the completed tool result and final answer.

What We Tried

We tested PR #31505, which flushes missed parts after the stream loop finishes:

await finish()
if (!args.attach) await flushParts(result.data?.parts)

That did not fix our case because finish() itself can hang waiting for the event stream to observe session.status: idle. Since flushParts() runs after finish(), the fallback is never reached.

Custom Patch

We changed JSON mode to flush returned prompt/command parts before waiting for stream completion:

async function finishBestEffort() {
  if (args.format !== "json") {
    await finish()
    return
  }

  await Promise.race([
    finish(),
    new Promise<void>((resolve) => setTimeout(resolve, 1000)),
  ])
}

Then changed both session.command and session.prompt paths from:

await finish()
if (!args.attach) await flushParts(result.data?.parts)

to:

if (!args.attach) await flushParts(result.data?.parts)
await finishBestEffort()

Why This Works

Once client.session.prompt() or client.session.command() returns, result.data.parts contains the completed assistant parts. For --format json, emitting those parts immediately avoids depending on the event stream’s idle signal.

The stream is still given a short best-effort drain window, but output delivery no longer blocks forever on it.

Plugins

No response

OpenCode version

0.17.7

Steps to reproduce

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Screenshot and/or share link

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Operating System

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Terminal

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