# Objective
Simplify code in the `SingleThreadedExecutor` by removing a special case
for exclusive systems.
The `SingleThreadedExecutor` runs systems without immediately applying
deferred buffers. That required calling `run_unsafe()` instead of
`run()`, but that would `panic` for exclusive systems, so the code also
needed a special case for those. Following #18076 and #18406, we have a
`run_without_applying_deferred` method that has the exact behavior we
want and works on exclusive systems.
## Solution
Replace the code in `SingleThreadedExecutor` that runs systems with a
single call to `run_without_applying_deferred()`. Also add this as a
wrapper in the `__rust_begin_short_backtrace` module to preserve the
special behavior for backtraces.
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