I wonder if that has anything to do with this error?

java.lang.RuntimeException: java.lang.IllegalAccessException: Class
com.google.inject.ConstructionContext$DelegatingInvocationHandler can not access a
member of class CyclesGuiceTest$Writable with modifiers "public abstract"
	at
com.google.inject.ConstructionContext$DelegatingInvocationHandler.invoke(ConstructionContext.java:114)
	at $Proxy5.write(Unknown Source)
	at CyclesGuiceTest$Node.write(CyclesGuiceTest.java:97)
	at CyclesGuiceTest$Node.write(CyclesGuiceTest.java:97)
	at CyclesGuiceTest.testWithGuice(CyclesGuiceTest.java:18)

I was checking to see what happened when I put in a cycle using only constructors.  I
assumed that at some point there would be an error saying "you can't do that" and I
would make backlinks into setters, and ran into this undocumented (?) proxy thing. 
Maybe the real error is that this is not a Helpful Error Message.

This appears to be a Sun bug related to inner classes:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4071957

We do need better error handling here though. There's actually a TODO in the code:
http://fisheye3.cenqua.com/browse/google-guice/trunk/src/com/google/inject/ConstructionContext.java?r=253

While cleaning up the test case, I found that adding "public" in a few places fixed
the problem. 

So, it's nothing really to do with cycles.  But I was surprised that when I moved
some dependencies from constructors to setters to break cycles, so that no proxy is
really necessary, they are still there.

 Issue 349  has been merged into this issue.