#150 Avoid Windows libuv assertions on CLI errors

Summary

• replace forced process.exit calls in the shared CLI error path with exitCode plus a private control-flow error
• let the command guard absorb already-reported exits without printing twice
• preserve immediate command abortion and exit status 1 while allowing Node to drain active handles safely

Verification

• npm run typecheck
• 16 util tests, including a regression assertion that die never calls process.exit
• npm run build
• 50 Windows local-error runs with a fresh detached update check each time
• 20 Windows API-error runs with a fresh detached update check each time

Windows regression

Expected API failures could race process.exit against the detached update-check child and abort in src\win\async.c with UV_HANDLE_CLOSING. All 70 stress runs now exited cleanly with code 1 and no assertion or leaked CliExit stack.

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Summary by cubic

Replaces forced process.exit calls in the CLI error path with exitCode plus a private control-flow error, so Windows no longer races the detached update-check child and hits libuv assertions (UV_HANDLE_CLOSING). The command guard absorbs the new CliExit error, preventing duplicate error output. Errors still print to stderr and exit with status 1.

Verification

• Runs typecheck, build, and 16 util tests, including a regression assertion that die never calls process.exit.
• 70 stress runs on Windows with fresh detached update checks exited cleanly with code 1, no assertions or leaked stacks.
• Tests now restore process.exitCode in finally blocks and scope stderr/stdout spies per test.