[raiseCatError]

Scope

Review follow-up for #416, stacked after #419. Keep /track in v0.21.

• Emit a scheduler change when each refresh begins, so the existing live presenter can show refreshing… during a slow run rather than waiting until completion.
• Release the per-tracker live-row height bookkeeping on stop, while retaining the stopped state and once-only final transcript snapshot.
• Assert that stop releases this bookkeeping in the app integration test.

Release gates

CI and focused tests must pass. Physical Ghostty/Terminal.app QA is still required, as are the three flaky-test fixes and post-merge checks. No release or merge attempted. /track continues to be window-owned; persistence across detach is deferred.

Refs #393, #410, #416.