Subagent detail view footer shows the parent session's model, not the agent's actual model

Bug

When navigating to a background subagent's detail view, the footer displays the parent session's model rather than the model actually serving the subagent.

Repro / evidence

• Main session running on claude-fable-5.
• Dispatched subagents via the Agent tool with explicit model overrides (sonnet, haiku).
• The subagent detail view footer showed "Fable 5" for these agents.
• Ground truth from the subagent transcript JSONL (tasks/<agentId>.output): every request line records e.g. "model":"claude-sonnet-5" (or claude-haiku-4-5-20251001 for the haiku dispatch) — the override was honored; only the footer is wrong.
• Also reproduced with the model param omitted: transcript shows claude-sonnet-5 (the general-purpose default), footer still shows the session model.

Impact

Misleads users auditing model selection/cost. In our case it twice triggered false alarms that expensive top-tier models were serving mechanical tasks (and once led the assistant itself to wrongly "confess" to a dispatch mistake based on the footer). Transcript grep is currently the only reliable way to see a subagent's real model.

Expected

Footer should show the model recorded in the subagent's own transcript (or show both: "agent: sonnet-5 · session: fable-5").

Environment

Claude Code 2.1.198, macOS (darwin 27.0.0).