V2: subagent completion concatenates independent text blocks #53039

Description

V2 removes the boundary between independent text blocks when delivering a subagent's final message to its parent. SubagentCompletion.text joins them with an empty string.

For example, two saved text blocks ending in production is unchanged. and starting with ## Result reach the parent as production is unchanged.## Result. The Markdown heading is already malformed before rendering.

Plugins

Reproduced in a Core test without plugins.

OpenCode version

2.0.22; also present in 2.0.18 and the current v2 branch.

Steps to reproduce

1. Complete a subagent message with two text parts: The files are unchanged. and ## Result\n\nDone.
2. Deliver that completion through the foreground subagent tool.
3. Observe The files are unchanged.## Result in the parent result, rather than two paragraphs.

The proposed fix inserts a blank line between independent nonempty text parts. Single-part content and the empty-result fallback remain unchanged.

Screenshot and/or share link

The regression is reproduced by packages/core/test/tool-subagent.test.ts; no session containing private data is shared.

Operating System

Linux x64.

Terminal

OpenCode Desktop 2.0.22; the defect also reproduces directly in Core.