[FEATURE]: Show subagent model in session tree / subagent view #23028

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

When OpenCode spawns subagents, it would be helpful to show the model used by each subagent in the session UI. This allows users to quickly see which model each (sub)agent is running on when reviewing plans, subtasks or session trees.

Example:

• Plan — GPT-5.4
  • General — GPT-5.4-mini
  • Build — Sonnet-4.5

This could appear in the session tree, behind a toggle in the session view, or in the sidebar if work is being done there to display running subagents. Toggling could show active subagents and their models, making it clear at a glance which models are handling tasks.

Benefits:

• Makes multi-agent/step runs easier to understand
• Lets users confirm which model is being used for each agent
• Useful for troubleshooting and for mixed fast/strong reasoning agent workflows

Related context:

• There are existing PRs/changes for subagent tree navigation and for subagent variants
• There is interest in seeing model information but no feature specifically adds a model display to the UI

I am not requesting to show whether each agent receives the model by inheritance or explicit config; only to display each agent's effective model.