Merge branch 's3-async-tmux' into s3-followups

docs/SERVER-MODE.md

@@ -567,7 +567,13 @@ a pane really is. Each case below is refused or bounded, with a test in
 - **A member's stopped or flooding tmux server.** Every call on it has a 3 s
   limit and a 1 MiB answer cap; one that hit either is not asked again for a
   minute. Meanwhile only that member's panes count as unknown (kept, not
-  ended); everyone else's are still checked. Every other synchronous call
+  ended); everyone else's are still checked. Listing a member's panes (every
+  poll: the pane list, the workspace list, the 10 s heal beat, the liveness
+  reaper) never waits for them: it runs in the background and the poll reads
+  its last answer, so a stopped server stalls nobody. Until a first answer,
+  or once the last is 15 s old, their panes count as unknown too. A call a
+  click makes on a member's pane (start, type, stop) still waits, up to the
+  3 s. Every other synchronous call
   that runs as a member (git in their folder, `write-as`) stops after 5 s.
 - **A member's huge or sparse files.** Transcripts and journals are read line
   by line with a 64 MiB cap per line (a 512 MB line used to crash the server);