[UI] Token counter shows cumulative I/O during execution, switches to final context size on completion

The token counter displayed for subagents shows inconsistent metrics depending on task state:

• During execution: Shows cumulative tokens transferred (all API round-trips)
• After completion: Shows final context size

This creates confusion where a task might display 14.2M tokens while running, then snap to 89.8K upon completion.

Screenshots

Running agent (Phase 7):

10m 0s · 14.2M tokens · 118 tools

Completed agent (Phase 8):

✔ Completed · 10m 9s · 89.8k tokens · 59 tools

Both phases ran for ~10 minutes on similar enum migration tasks. Phase 8 lshowed similar multi-million token counts during execution before settling to 89.8K.

Expected behavior

Either:

1. Show consistent metric (cumulative tokens) in both states, or
2. Display both values: Context: 89.8K · Total consumed: 14.2M

Why it matters

• Users see alarming token counts (18-20M) without understanding what they represent
• Makes cost estimation difficult during long-running tasks
• Creates confusion about actual context window usage vs billing

Environment

• OS: macOS