Transform OpenCode "task" tool calls with subagent_type into unified
Agent card display: rewrite as "Agent" tool with subagent_type, prompt,
description, and model; compute duration from time fields; query
sub-agent session parts from SQLite for nested tool call lists; extract
<task_result> content to strip preamble noise from agent output; guard
Streamdown code plugin against unsupported Shiki language identifiers
(e.g. "##", "function") in fenced code blocks from tool output.
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