Allow external spool workflow with Filament Track Switch

[PollyBot13]

Summary

This draft addresses bambulab/BambuStudio#10328 by allowing the existing per-nozzle external spool virtual slots to be selected in Studio when a Filament Track Switch is installed.

Current behavior blocks external spool selection in the FTS / dynamic mapping dialog and tells users to uninstall the Filament Track Switch. That forces users to physically unplug/remove the accessory for cases where the filament can be routed externally:

• normal external spool through the external buffer
• TPU Feed Assist / flexible filament routed directly to a toolhead
• PTFE/Y-split bypass setups where FTS remains installed for the other nozzle

Implemented Scope

This is intentionally a small Studio-side change:

• keep existing virtual external slots:
  • 255 / main-right external spool
  • 254 / deputy-left external spool
• allow those virtual slots to remain selectable in LEFT_AND_RIGHT_DYNAMIC mapping mode
• when sliced nozzle data is available, keep only the external slot matching the filament's sliced nozzle selectable in dynamic mapping mode, so a left-nozzle filament cannot be mapped to the right external slot and vice versa
• remove the click-handler guard that silently ignored virtual external slots in that mode
• allow the device-page external-slot Load / Unload actions to reach the existing assisted feed-direction flow when the Filament Track Switch is installed
• do not require Filament Track Switch setup/readiness for Ext-L / Ext-R, because those virtual external slots represent user-assisted external routing that may intentionally bypass the switch
• persist device-page filament choices for Ext-L / Ext-R by sending material settings for virtual slots and preserving the correct virtual tray id (254 or 255)
• replace the old "uninstall Filament Track Switch" warning with guidance that the external filament must be routed through the external buffer or directly/bypassing FTS to the selected toolhead

Studio sends the same existing external virtual-slot mapping for both physical routing cases; the operator/printer must enforce the actual route.

Non-goals

This does not implement a full routing graph or claim that the Filament Track Switch can retract arbitrary external spools.

It also does not add a persisted via buffer versus direct bypass mode, because I have not found an existing printer/job protocol field for that distinction in Studio. The patch only re-enables the existing external virtual-slot mapping that Studio already serializes.

Desired Product Behavior

The desired product behavior is:

• FTS may remain electrically connected and installed.
• A selected nozzle may use an external spool.
• The external spool may be routed through the existing buffer path for normal filaments, or directly to the selected toolhead for TPU/flexible-feed-assist setups.
• FTS/AMS can still be used for the other nozzle when the mapping is otherwise valid.

If printer firmware currently rejects external virtual-slot mapping while FTS is installed, this Studio patch will need a matching firmware capability/update. In that case, the same UI change should be gated behind a firmware/capability flag instead of being rejected as a hardware impossibility.

Validation

• git diff --check
• local macOS arm64 build:
  • dependencies: CMAKE_BUILD_PARALLEL_LEVEL=8 ./BuildMac.sh -d -a arm64 -x -c Release
  • app: ninja -C build/arm64 -j8
  • packaged app: build/arm64/BambuStudio/BambuStudio.app
• local X2D LAN UI smoke test with Filament Track Switch present:
  • bound 20P9BJ620301973 (LAN) from an isolated test profile
  • sliced bundled Bambu_Cube.stl with the X2D preset
  • confirmed the filament-switcher path is active in Studio
  • opened the send/mapping dialog without clicking Send
  • confirmed the selector shows Ext-L/Ext-R plus the new route/firmware note
  • confirmed Ext-L is selectable for the sliced nozzle side while Ext-R is shown but disabled
• source inspection of the device-page load menu confirmed the old FTS guard also blocked virtual external-slot Load / Unload; this patch removes that blanket block so both assisted operations can proceed through the existing feed-direction flow without requiring FTS readiness for Ext-L / Ext-R
• source inspection of the device-page filament setting path confirmed virtual external slots were not persisted reliably: ordinary filament presets were not sent unless the slot was already classified as third-party, both virtual slots were serialized as tray 254, and the response parser only refreshed the main/right virtual slot. This patch sends virtual-slot material settings explicitly and keeps Ext-L / Ext-R distinct.
• Code inspection of existing external virtual-slot mapping path:
  • src/slic3r/GUI/DeviceCore/DevDefs.h
  • src/slic3r/GUI/DeviceCore/DevMapping.cpp
  • src/slic3r/GUI/SelectMachine.cpp
  • src/slic3r/GUI/AmsMappingPopupUpdate.cpp
  • src/slic3r/GUI/AmsMappingPopup.cpp
  • src/slic3r/GUI/StatusPanel.cpp

Still not validated:

• firmware/printer acceptance of 254/255 external virtual-slot mapping while FTS is installed

Addresses #10328.