*sigh* my post was lost.

The problem: After playing the game for a few hours, it will freeze for a short time, then will freeze repeatedly until it stops completely. It must be closed and reopened, somewhere between when the freezes become obvious and when it stops completely, for it to return to a playable state.
There is a way to make it stay playable for longer, at least the length of time I have tested it for (a larger number of hours)
The java arguments -XX:+UseConcMarkSweepGC and -Xmx1024M (or similar number depending on available RAM) are required for normal operation of the software.

I, Khonkhortisan, hereby hold you, Three Rings, to this text: "Getdown will allow any arguments to be passed to the underlying JVM, not just a particular set that have been declared acceptable by the application deployment system." http://www.staging.threerings.net/getdownRationale.html
It does not appear that the spiral shell script can be modified to have getdown pass the options on to the program. Either the arguments are applied to getdown itself, or getdown fails with WARNING r.a: Invalid app_dir.
Because getdown is Unfit for this Particular Purpose, I make the claim that I am not held to Terms of Service Sections 6-1 (https://github.com/threerings/getdown) and 6-13 (you leave me no choice) in this very limited case. (nor am I held to 5, playing it outside the web player)
The method of running the shell script to run the updater to run the game to quit the game to save the default arguments in launcher.log to edit those arguments to pass directly to the game requires either bypassing the updater and running it manually when an version mismatch is encountered, or running the game twice - once for an update check, once to run in a playable way.
The method of adding the arguments to getdown.txt, writing the md5sum of getdown.txt into the first line of digest.txt, removing the last line of digest.txt, writing the md5sum of digest.txt into the last line of digest.txt does not require bypassing the updater, but does require power cycling the game when an update happens.
The method of compiling a modified getdown capable of passing arguments (untried) requires a modified md5sum for it in digest.txt, unless a patch is submitted, accepted, and included in a game update.

Please tell me how to start Spiral Knights in such a way that it will not halt, that it may update itself, and that it only needs to be started once per playing session, even when it has updated itself.

Until such a time as there is a final solution, I present a temporary one:

#!/bin/bash
#./spiralwrapper.sh
runspiralknightswithoutchanginganything=false

function testoriginality {
grep ' getdown.txt ' getdown.txt > /dev/null
isoriginal=$?
}

function applyarguments {
sed -i 's/ getdown.txt / getdown.txt.modified /' getdown.txt
sed -i '/jvmarg = -Xmx256M/d' getdown.txt
sed -i '/optimum_jvmarg = -Xmx512M/d' getdown.txt
echo "jvmarg = -XX:+UseConcMarkSweepGC" >> getdown.txt
echo "jvmarg = -Xmx1024M" >> getdown.txt
sed -i "1 c\getdown.txt = `md5sum getdown.txt | awk '{print $1;}'`" digest.txt
sed -i '$ d' digest.txt
echo "digest.txt = `md5sum digest.txt | awk '{print $1;}'`" >> digest.txt
}

function startandwait {
./spiral
clientpid=""
while [ "$clientpid" == "" ]
do
clientpid=$(ps u -C java | grep projectx | awk '{print $2}')
done
}

if $runspiralknightswithoutchanginganything;
then #remove JVM options
testoriginality; if [ $isoriginal == 1 ]
then
echo -n "Last run, restoring JVM arguments... "
echo "Update me!" >> getdown.txt
startandwait
echo "May the ice bring them wisdom."
else
./spiral
fi
else #add JVM options
testoriginality; if [ $isoriginal == 0 ]
then
echo -n "First run, fixing JVM arguments... "
applyarguments
echo "They wish you cold winds." #freedroidrpg
fi

echo -n "Waiting for updater to finish... "
startandwait
echo "Client started."

testoriginality; if [ $isoriginal == 0 ]
then
echo "Files updated, restarting to reapply JVM arguments!"
applyarguments
kill $clientpid
echo -n "Waiting for updater to do nothing... "
startandwait
echo "Started client for real this time."
fi
fi

Yet again, my whitespace is collapsed.