FixedPlacementPolicy (the default placement policy) never consulted
maxLoad, so an at-cap default was chosen anyway on every unqualified
spawn -- the cap was advisory, not enforced, for the one policy every
config uses by default. weighted/round-robin already gated on it via
PlacementPolicyUtil.available().
Extract the "at cap" predicate into PlacementPolicyUtil.atCap(ctx, c)
so all three policies share one definition, and consult it at both of
FixedPlacementPolicy's filter sites (the default fast path and the
candidate walk), mirroring the existing weightExcluded pattern. An
at-cap default now falls through to the next candidate instead of
refusing the spawn -- only when every candidate is unusable does the
policy still throw, naming the cap in the message. Update the class
javadoc (five exceptions -> six) and the reason-priority comments to
match CompositePeerLauncher's explicit-spawn order (quarantine,
cooling off, max load, model-off).
Dai Ha