## What happened

`~/.config/omarchy/extensions/omarchy-menu.jsonc` documents that reusing an existing menu id merges into the stock entry:

> `// root menu. Reuse an existing id to override/extend it.`
> `// Example: replace the default About action by reusing the same id. Existing`
> `// fields are kept unless overridden.`

In practice, redefining an existing id **replaces** every field. Overriding only `action` silently drops the entry's `icon`, `label`, `when`, `checked`, `description`, `aliases`, `target` and `provider`.

Overriding just the logout action:

```jsonc
"system.logout": {"action":"..."},
```

renders the row with no icon and the literal id `system.logout` as its label, instead of 󰍃 / "Logout".

## Expected behavior

Per the documented contract, unspecified fields should be inherited from the stock entry.

## Root cause

`shell/plugins/menu/MenuModel.js`. `mergeMenuSources()` (line 65) does implement the documented field-wise merge:

```js
var merged = {}
for (var k in prior) merged[k] = prior[k]
for (var k2 in entry) merged[k2] = entry[k2]
```

But each source is normalized *before* it reaches that merge. `parseMenuJsonc()` (line 41) calls `normalizeItem()` (line 13) on every raw entry:

```js
icon: value.icon || "",
label: value.label || id,
...
when: value.when || "",
```

So by merge time the user entry is a fully-populated object where every unspecified field is present as `""` (or the id, for `label`). `for (var k2 in entry)` then copies those empty values over the stock ones — "absent" and "explicitly empty" are indistinguishable, and nothing is ever left un-overridden. `label: value.label || id` is exactly why the row falls back to showing `system.logout`.

## Why it matters beyond cosmetics

`when` is wiped the same way. A user overriding only the action of `system.hibernate`:

```jsonc
"system.hibernate": {"action":"..."},
```

loses `"when":"omarchy-hibernation-available"`, so the row shows unconditionally on machines where hibernation isn't available. Same hazard for `system.suspend`'s `when` and for any `checked` condition.

## Steps to reproduce

1. Add `"system.logout": {"action":"omarchy-system-logout"},` to `~/.config/omarchy/extensions/omarchy-menu.jsonc`
2. `omarchy menu refresh`
3. Open the menu — the Logout row now has no icon and is labelled `system.logout`

## Suggested fix

Merge the raw JSONC values first and normalize once at the end, rather than normalizing per source. Either have `parseMenuJsonc()` return raw `{id, value}` pairs and run `normalizeItem()` after `mergeMenuSources()`, or have `normalizeItem()` only set keys actually present in `raw` and apply the defaults in a final pass.

## System details

- Omarchy version: 4.0.4-1