# Nexus enablement

**🟠 Advanced · Lesson 08**

TURNING THE NEXUS ON - and discovering that it does NOT climb the same ladder Aether does. Lesson 07 taught Aether's rule: freeze, then activate, then bring the subsystem up, in that order, or it refuses. Nexus reaches the same destination by a different route, and knowing which subsystem you are talking to is the whole lesson.

THE NEXUS PATH nexus = md.Nexus() # process-wide, no args config = nexus.create_configuration() nexus.activate(config) # installs AND finalizes nexus.is_activated -> True

THREE ASYMMETRIES WITH AETHER, ALL REAL, NONE ACCIDENTAL:

1. THE FACTORY PRE-DEFAULTS. Aether's create_configuration() hands back a bare config and you call with_defaults() yourself. Nexus's create_configuration() applies the default property set before returning. Same verb shape, different starting state.

2. ACTIVATE FINALIZES FOR YOU. Aether refuses a merely-frozen config and makes you call configuration.activate() first - two bits, your responsibility. Nexus.activate() finalizes the installed configuration on its way through. You do not pre-seal it, and trying to reason about it with Aether's rule in your head will mislead you.

3. NEITHER FACTORY INSTALLS. This one they agree on, and it is worth stating because it is the part people assume: create_* is a FACTORY. It builds and hands over. Nothing is wired anywhere until you pass it to activate().

TWO BITS AGAIN, DIFFERENT NAMES nexus.is_configured - a configuration is installed nexus.is_activated - the subsystem is up Same shape as frozen/activated in lesson 07. Configuration presence and subsystem liveness are always separate questions in melder.

## Before you run

Use the [Advanced guide](../../advanced/index.md) for prerequisite concepts. Run from a checkout with Melder installed and Python 3.14 free-threading selected. The collection download includes the level's local helper modules.

## Run the saved script

```bash
python UX_and_AIX_experiences/03_advanced/08_nexus_enablement.py
```

```powershell
py -3.14t UX_and_AIX_experiences/03_advanced/08_nexus_enablement.py
```

{download}`Download this collection <../../downloads/advanced-examples.zip>` · [Source on GitHub](https://github.com/Synaptic724/melder/blob/1211e838099a342c9dde48f064b1e772b6060e13/UX_and_AIX_experiences/03_advanced/08_nexus_enablement.py)

## Public surface

md.Nexus, md.NexusConfiguration,
                   create_configuration, activate, deactivate
                   (frame mode passed as the string "single")

## Code

```{literalinclude} ../../downloads/03_advanced/08_nexus_enablement.py
:language: python
:linenos:
```

## Check the outcome

The script contains its own assertions or demonstrated refusal paths. Run it to evaluate those checks against your installed version. The code above is taken directly from the saved file; no run output is invented here.

[More advanced examples](index.md) · [Level guide](../../advanced/index.md)

## Related guides

- [Enable Nexus and open a Rift](../../advanced/nexus.md)

## API contracts

- [Nexus](../../reference/api/inspection/nexus.md)
- [NexusConfiguration](../../reference/api/inspection/nexusconfiguration.md)