ui: give the startup block a static settled form

[hbrooks]

Summary

• The settled startup block rendered the session's LIVE status, so an old session opened with ✓ Session asleep as its first line. It now shows a static record of the start: ✦ Cloud agent session on ellipsis.dev + ⎿ Sandbox ready in 42s · 31 log lines, compressed the way a collapsed tool run is.
• Live headline renamed to Starting cloud agent…; session_idle / session_resumed settle the block without rewriting its headline.
• Falls back to Sandbox started · N log lines when no duration can be derived (old feeds with no phase_timings, wakes).

Test plan

• bun run typecheck
• bun run test (467 pass)
• agent session connect on an old, asleep session: opening line reads as a past event, no live status
• agent session connect on a fresh start: live headline ticks, build/setup log still streams, then collapses to the summary

Important

Changes the settled startup block to show a static one-line summary instead of rendering live session status.

When a session startup finishes, the block now displays a compressed record of the start event — e.g. Cloud agent session on ellipsis.dev with Sandbox ready in 42s · 31 log lines — the way a collapsed tool run does. Previously it would render live status (e.g. "Session asleep"), which made old sessions open with "Session asleep" as the first line of the conversation, which is not what happened first.

• Live headline renamed to Starting cloud agent… while the session is coming up; the three settlement events (session_idle, session_resumed, sandbox_ready) now settle the block without rewriting its headline.
• Added SandboxState.readySeconds to track sandbox provisioning duration from phase_timings; settlement builds a static one-line summary with sandboxSummary() instead of a live status.
• sandboxRows() now renders two forms: a live version with ticking headline + log tail, and a settled version with the static summary line under the opener.
• Falls back to "Sandbox started · N log lines" when duration is unavailable (old feeds, wakes).

^{This description was created by for b5ee90d. It will automatically update as commits are pushed.}

[ellipsis-dev]

Important

Looks good to me! 👍

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