Claude Code sessions can now message each other over a Unix socket on your own machine. I had 23 sessions running and only 14 of them could see each other. Here is what the message channel fixes, what it cannot fix, and why the guard I trusted for months was never a guard at all.
A git worktree isolates your working directory and your index. It does not isolate the stash stack, which is shared by every checkout in the repository. Here is what I measured on git 2.50.1, why MERGE_AUTOSTASH escapes the problem through an accident of spelling, and how one defensive stash can make a worktree look safe to delete.
Merge queues, merge trains, and speculative merging all rest on one assumption nobody states: that a per-branch green tick means the code works. Our own CI runs no unit tests at all, and master went red twice in two days from pull requests that were each green on their own. Here is what to build before you buy the queue.