[StRigaud]

Fixes #82

Root cause — In FijiApposeTaskListener.errorListener() (src/main/java/fiji/plugin/appose/cellpose/FijiApposeTaskListener.java:114), the env-name was extracted with two independent whole-string searches:

str.substring( str.indexOf( "The" ) + 3, str.indexOf( "environment" ) )

On the first run the str passed by Appose's error stream is a large accumulated buffer (length 39273 in your trace), not a single line. In that buffer:
indexOf("The") matches the "The" in the final The … environment has been installed. line → begin = 39232
indexOf("environment") matches the first "environment" that appeared much earlier in the log → end = 586
So substring(39232, 586) has begin > end → StringIndexOutOfBoundsException. It's non-blocking (thrown on a background stream-reader thread, cellpose keeps running) and doesn't recur because subsequent runs emit a short buffer where the two indexOf calls happen to align.

Fix — Anchor on the real phrase and search backwards from it, with bounds guards:

final int envIdx = str.indexOf( "environment has been installed." );
final int theIdx = str.lastIndexOf( "The", envIdx );
final String envName = ( theIdx >= 0 && theIdx + 3 <= envIdx )
        ? str.substring( theIdx + 3, envIdx ).trim()
        : "";
IJ.showStatus( "Python environment " + envName + " is ready." );

lastIndexOf("The", envIdx) finds the "The" belonging to the same line as the installed-phrase, so begin never exceeds end regardless of buffer size, and the guard falls back to an empty name if the pattern isn't found. Uses of .trim() to fixed the missing space before "is ready." for a cleaner status message.

Still to be tested to be sure all is good before merge!