MCP tools don't populate output.output in the tool.execute.after hook —
the MCP content flows through OpenCode's internal parts pipeline instead.
This caused a crash: undefined is not an object (evaluating 'text.length')
in the truncate function.
runHook() return value was being discarded. The hook was called but its
additionalContext was never appended to output.response, so reminders
never appeared in the model's tool result.
experimental.chat.system.transform fires for task-spawned subagent sessions
after the task prompt (user message) is already in the conversation. Pushing
to output.system at that point places a system message at a non-zero position,
which Qwen3.6's strict Jinja chat template rejects with 'System message must
be at the beginning.'
Move session-start.sh injection to chat.message (first turn guard via
initializedSessions). Injected as a synthetic text part via unshift(), which
has no position constraints.
