I was getting the following error message when trying to build a swf that used an Alchemy-generated swc:

/home/failrate/flash_project/flex_development/alchemy/samples/stringecho/as3/EchoTest.as(9): col: 15 Error: Type was not found or was not a compile-time constant: CLibInit.

var loader:CLibInit = new CLibInit;
^

/home/failrate/flash_project/flex_development/alchemy/samples/stringecho/as3/EchoTest.as(9): col: 30 Error: Call to a possibly undefined method CLibInit.

var loader:CLibInit = new CLibInit;
^

/home/failrate/flash_project/flex_development/alchemy/samples/stringecho/as3/EchoTest.as(4): col: 28 Error: Definition cmodule.stringecho:CLibInit could not be found.

import cmodule.stringecho.CLibInit;

I couldn't find any references on-line, so I reread the getting started documentation [http://labs.adobe.com/wiki/index.php/Alchemy:Documentation:Getting_Started] and
found a brief mention near the middle:

Use the following command to compile the ActionScript code using MXMLC:

mxmlc -library-path+=../stringecho.swc --target-player=10.0.0 EchoTest.as


This turned out to be the correct solution, but googling didn't yield a response, because the given error messages weren't in the troubleshooting section.