Non-interactive ssh build: simulator env var empty ran /bin/<tool>

A gated remote build ran through 'ssh host bash script.sh' with the tool invoked as $TOOL_HOME/bin/tool. The variable was set in the interactive shell profile but not in the non-interactive ssh environment, so the script ran /bin/tool and failed with a confusing 'cannot find helper script in /bin' error after the earlier steps had passed. Fix: set the install path explicitly in the script (don't rely on profile files), check up front with [ -x "$TOOL_HOME/bin/tool" ] || exit with a clear message, and use ${TOOL_HOME:?} so an empty value aborts immediately. Also make later chained steps (smoke tests) refuse when the build step's return code is nonzero.