[FEATURE] Show the actual model of each spawned subagent in the task/progress UI

Problem

When the main agent spawns subagents via the Agent tool (optionally with a model override), there is no way to see in the UI which model each subagent is actually running on — neither in the live progress/task list, nor in the completion notification.

Today the only way to verify is to grep the subagent transcript JSONL for the "model" field:

grep -o '"model":"[^"]*"' /tmp/claude-.../tasks/<id>.output | sort | uniq -c

This matters because model overrides are easy to get wrong silently (e.g. inheriting the parent session model instead of the requested one), and the cost difference between tiers is large. Users delegating work to cheaper/stronger models specifically want to confirm the delegation actually happened.

Proposed solution

Display the resolved model id (e.g. opus-4-8) next to each subagent in:

• the live background-task / progress view,
• the task completion summary,
• ideally also in the Agent tool result returned to the parent agent at launch time.

Context

Found while orchestrating parallel Opus subagents from a session running on a different model — verifying the override required manual transcript inspection.

🤖 Generated with Claude Code