Strip the card chrome and rewire /agents to feel like peeking into the
child agent's stream:
- subagents store: single `stream` of typed entries (thinking/tool/progress/
summary) replaces the parallel notes/thinking/tools arrays. Drop unused
fields (toolsets, depth, apiCalls, reasoningTokens, sessionId).
- agents view: no OverlayCards, no boxed stream, no per-row borders. Goal +
status pill + indented stream lines, full row width.
- Group root spawns into "Delegation N" sections when batch shape + spawn
time match — hides task-index interleaving and makes hierarchy obvious.
- Sort tree by spawn time, then task_index. Step indicator is one colored
pill (primary while running, emerald when done) inside the row, not a
trailing pill that wrapped under the chevron.
- Tree picks up `subagent.start` (not only `spawn_requested`) and prunes
delegate-tool fallback rows once native subagent events land for the
session — fixes duplicate "Delegated task" rows alongside the real ones.