Every checkout that boots Hermes commits its own dependency state under
<home>/installs/<sha256(path)[:16]>/ (venv, test venv, PM runtime; ~200 MB
each) and nothing removed it when the checkout went away. On a host that
runs `hermes -w` campaigns the directory held 499 entries / 92 GB, of which
402 (80 GB) belonged to worktrees and scratch clones that no longer exist.
The state dir already records its checkout in inputs/.project-root. A new
pm/install_states.py lists entries whose recorded checkout is gone and
removes them unless something could still be reading them (install lock
taken, or a generation lease held). `pm gc` runs it and reports the count;
the startup worktree pruner runs it after its own reaping so a removed
worktree's state follows the tree instead of outliving it.
ef4b046808