tenx 0.27.3 — a dispatched worker can no longer hijack the host tool install

Worktree isolation covered the files a worker writes, not the host tool environment it can reach.

The incident

Dogfooding a live Herdr dispatch, a worker installed from inside .tenx/worktrees/SPC-037-T1, leaving an editable pointer at that worktree's src. tenx reconcile removed the worktree, and the operator's global tenx died with:

ModuleNotFoundError: No module named 'tenx'

The tool that should have reported the damage could not run to report it.

What ships

• The brief forbids it. Every dispatched worker is now told the worktree
  is deleted at teardown, that any install pointing at it keeps pointing at a
  vanished path, and to verify with python3 -m tenx and
  python3 tests/smoke_test.py --module instead. An install requirement gets
  reported, not performed.
• Dispatch records a snapshot. Every receipt carries the host install's
  resolved source path, captured before the worker runs.
• Teardown checks. tenx reconcile and tenx abort verify the installed
  tenx command after removing the worktree and report the breakage with the
  recovery command. The merge still completes — repairing a host-level tool
  stays an explicit operator decision.
• tenx doctor reports it when the running tenx resolves inside
  .tenx/worktrees/.

Why two signals

The snapshot comparison alone was not enough, and the first implementation
missed the real incident because of it: the snapshot only sees the interpreter
reconcile runs in, while the damage lands on whichever interpreter backs
the globally installed CLI. Teardown therefore also asks that command directly
whether the operator can still run tenx.

Verified

Against a faithful reproduction — an isolated venv whose install pointed at a
dispatch worktree, with the worktree then removed — tenx --version failed with
ModuleNotFoundError before the fix and the teardown reported it after, with
the merge still landing. 15 new smoke checks pass in both module and
install-path modes.

Upgrade with tenx update.