Master's transactional loader made the invalid-provider PTY case regress:
the HMR main watcher's initial scan refreshed the include mid-initial-apply,
the concurrent group updates stranded the include fiber, and once serialized
the failing apply's rollback deadlocked on HMR's refresh drain — dsh exited
13 with no diagnostic and the terminal stranded, the exact symptom this
branch fixes. Serialize every include child-tree mutation through one queue
and pass ignoreInitial to the HMR main watcher; the failing boot now settles
through boot()'s labelled rejection with the tree disposed and exit 1. The
PTY case asserts the settled diagnostic; the fail-loud release remains the
guard for rejections boot cannot see.
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