Wake reads waiting on /log, event and pty/data; one reader per consuming file; pty/ctl reads back

A read parked on a queue was retried only when some unrelated write had
to wait, so a follower of /log (and a reader of event or pty/data) slept
until then. Pushing a record now marks the turn parked, and giving the
turn up wakes them (measured: stuck past 3 s before, 0 s after).

event and pty/data consume what they read, so a second open for reading
is refused with rio's "file in use" (EBUSY through 9ns); writers still
get in, and pty/data queues output only for an actual reader. pty/ctl
reads back "winsize C R", in the words it takes.

/log fixes from review: a record longer than a read comes in pieces (a
shell read loop failed on long lines), every repeated message is logged,
a record bigger than the ring is cut to fit instead of emptying it, the
ring is reserved at boot so recording never allocates, and panes present
at boot are recorded first.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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