Serialize room drives through their actual member completion, freeze input
watermarks by retained entry identity, and share the same completion path
with handoff continuations. Stop discards queued work without releasing an
active owner early; rename follows the existing room binding.
Observe stranded replies for the hard-cap duration plus grace after the
foreground wait, and retain unresolved failures in collapsed Activity.
Never automatically retry an ambiguous failed submit within the same drive.
Adapted from the queue and boundary approach in #92041 by @enwaiax and
harvest-budget approach in #107193 by @Finn763; #106502 by @wadib identified
failed-submit watermark consumption. The implementation retains current
numeric watermark storage, room lifecycle bindings and serial round limits.
Related: #92003, #105247, #100026
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