Review follow-ups for the remote scrollback read.
The 1.5 s slot-wait bound was checked inside the task, so it only fired
once runWithRemoteSshLimit() had already handed over a slot, after
everything queued ahead of it. runWithRemoteSshLimit() now takes
`maxWaitMs`: a waiter that times out leaves the queue, rejects with
RemoteSshSlotTimeoutError, never runs and never touches `active`. The
history read uses it, and a slot timeout does not back the host off.
Only a transport failure backs the host off now (ssh exit 255, a
timeout, a spawn error, output that is not the script's), via
classifyRemoteAliveExit(). A remote command failing is about that
session only. A live run against a real host showed a missing session
comes back as exit 0 with empty markers, because the `| tail -c` pipe
takes tail's exit status, so markers that arrived without a size are
also per-session.
fetchRemoteScrollback() takes an optional runner as a test seam; tests
now cover the bounded wait, each back-off class, its expiry, and the
masked missing-session case. A source pin covers the `-S 0` capture
branch. The two seams that can drop rows at the join (rows that scroll
during the round trip, a taller shared client) are documented in
docs/remote-sessions.md, and the limiter's header and the remote-ssh
invariants now name the history read as an ssh consumer.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
