TL;DR: your jupyter packages are mismatched. Upgrade jupyter_core, ipykernel, and jupyter_client together and the kernel starts.

## The error
```text
ImportError: cannot import name 'secure_write' from 'jupyter_core.paths'
```

## Fix it
1. Upgrade the trio together:
   ```
   pip install -U jupyter_core ipykernel jupyter_client
   ```
   Expected: installs mutually compatible releases.
2. Verify the kernel launches:
   ```
   python -m ipykernel --version
   ```
   Expected: prints a version with no import error.
3. If you use conda, do the same from conda-forge in one command so the solver keeps them consistent.

## When this applies
Use this when starting a Jupyter kernel raises the secure_write error, typical after upgrading one jupyter package but not the others.

## When it does not apply
If the error names a different jupyter_core symbol, the same upgrade-together approach usually still applies. If no jupyter packages are installed, install jupyter fresh.

## Compatibility
jupyter_core 5.x with matching ipykernel 6.x and jupyter_client 8.x.

## Root cause
secure_write's location and signature shifted across jupyter_core releases while ipykernel and jupyter_client imported it from the old spot. Upgrading one side without the other leaves the import pointing at a name the installed version does not have.

## Edge cases
nbclient and nbconvert also pin against these; upgrading the whole jupyter stack at once avoids whack-a-mole. In locked environments, pin the trio to known-good versions together.