Extruder page management broken in Master branch

[nanoplane]

What happened?

if you have a printer settings tab with multiple extruders defined, multiple extruder pages are defined and numbered sequentially from "1". save this printer settings.
if you return to the printer page and add/remove extruders, the Extruder pages on the left are mangled. see attached image

This first screenshot is before modifying the count

This second screen shot is after modifying the count (add one extruder).

Project file & How to reproduce

no project file required....

1. create new printer setting
2. add extra extruders
3. save printer setting
4. add or remove extra extruders..
5. see the result.

Version

2.4.58.4

Operating system

MacOS 15

Printer model

any

[nanoplane]

The issue is in the Tab.cpp file, in the function TabPrinter::build_unregular_pages, line 3149.
at this point, if there are multiple extruders and the count is changing and it's not from_initial_build, then the value of n_before_extruders is incorrect.

This can be corrected by inserting the following before line 3149:

if (m_has_single_extruder_MM_page) {
    n_before_extruders++;
}

[nanoplane]

Here's another sample. Created by having "Single Extruder MultiMaterial" checked and clicking the up and down arrows of the "Extruders" field multiple times.

Before:

After:

Also note that there's a page missing !... the "Single extruder MM setup" page is missing until you play with the number of extruders....

[nanoplane]

The Single extruder MM setup page issue is another bug...

[supermerill]

I can see the problem with the single extruder mmu.
But I don't see any problem with your second screenshot. please enter in red the problematic thing.

[nanoplane]

Just look at the ordering of the Extruders.. and the fact that there are two entries for Extruder 3. specifically look at the second set of images rather than the first set....

[nanoplane]

I've created a fix for this at nanoplane:extruder_tab_fix.. two functions modified.