Web subagent tool summaries show output instead of command or filename #907

Problem

In the Web subagent transcript, completed Code Mode nested tool rows can display returned text as the action target: 已运行 200 7867 instead of the command, or 已读取 # Agent 工作规则 instead of the filename. This affects both the child detail panel and the clarity of execution evidence.

The child backend records start arguments, but the completion projection drops those arguments and native parent-call identity. Unpaired tool results then use their output as a summary. Separately, truncated raw argument previews can lose file/command targets even where structured target evidence exists, and the trajectory inspector renders omitted nested arguments as {}.

Expected behavior

• Keep recorded paths/commands in tool headings during execution, after completion, and when reopening saved child history.
• Keep output in the expandable result body.
• Report missing or truncated arguments accurately; do not infer a target or execution state from output.
• Preserve bounded projections and native call identities.

Scope

Fix the child event/transcript projection and related Web transcript/trajectory target rendering, with focused regression checks and the repository validation gates.

Implementation and diagnostic record

• Fix: fix(web): stabilize tool transcripts and concurrency recovery #909
• Reusable diagnostic path: Web development guide — tool headings and result evidence.
• Desktop evidence and narrow-screen evidence use synthetic public fixtures, not private sessions.