fix(cli): flush run parts after json stream idle

[maojindao55]

Summary

Fixes #31482.

• Track parts emitted by opencode run's event stream.
• After non-interactive session.prompt / session.command completes and the event loop reaches idle, flush any parts from the returned assistant message that were not emitted by the SSE stream.
• This keeps run --format json from exiting with missing text / step_finish events when session.status idle is observed before the final part updates are processed.

Context

Issue #31482 reports a reproducible case with opencode 1.16.2 where:

opencode -m volcengine-plan/kimi-k2.6 run --format json \
  --session <existing-session-with-tool-history> \
  "only output OK"

The assistant response and step finish were persisted in ~/.local/share/opencode/opencode.db, but stdout was empty or only contained step_start. A fresh session and a simple resumed session streamed normally. That points to the non-interactive run output path, not the model/provider.

The current loop exits on session.status idle. If that idle event reaches the loop before all final message.part.updated events are handled, the process can finish before emitting the response parts. The blocking session.prompt / session.command response already contains the assistant message parts, so this patch uses that response as a final precise flush source.

Testing

• git diff --check
• npm exec --yes bun@1.3.14 -- install --frozen-lockfile
• npm exec --yes bun@1.3.14 -- run --cwd packages/opencode build --single --skip-install --skip-embed-web-ui
• Built binary smoke test: opencode --version returned 0.0.0-fix/run-json-flush-parts-202606090832
• Manual real-model checks with the compiled binary:
  • new run --format json session emitted step_start, text, and step_finish
  • resumed run --format json --session ... emitted step_start, text, and step_finish

Note: the current dev build could not resume the original 1.16.2 local session because it returned Session not found for that legacy session. The fix was validated against a current dev session created by the compiled binary.

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

Based on my search, I found one potentially related PR:

Related PR:

• fix(session): retry empty stream truncations and discard partial parts #26167 - fix(session): retry empty stream truncations and discard partial parts
  • This addresses similar issues with stream handling and partial parts in session execution, which relates to your PR's focus on flushing message parts after stream idle.

However, it's addressing a different aspect (retrying empty streams and discarding partial parts vs. flushing non-emitted parts). The current PR (31483) appears to be the primary fix for this specific issue.

No duplicate PRs found.

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