A links record naming a file is where the emulator reads it: ROCKNIX links /storage/roms/bios/nds_bios_arm9.bin into DraStic's system folder (start_drastic.sh:37-41). $biosdir, ${biosPath} and $bios_path are the BIOS directory as RetroPie, EmuDeck and RetroDECK write it, and every place of those platforms was dropped as an unknown folder. A core name the launcher replaces is no longer packed when held: EmuDeck passes Complex_4627v1.03.bin to xemu (emuDeckXemu.sh:60-61), which never opens Complex_4627.bin.
NanoBoyAdvance opens general.bios_path, default bios.bin (src/platform/core/src/config.cpp:36 at 3bb6f478). gba_bios.bin is the path ROCKNIX's config.toml sets, recorded under launchers: in rocknix.yml.
Without the alias the entry met only PCem's and QEMU's bios.bin, 64 and 128 KB, which BIOSLoader refuses (bios.cpp:17-48). verify counted it held by name, so the launcher layer left it alone and the ROCKNIX pack gained PCem's image. A hashless entry whose every same-named copy fails its size is now not held, and the gba_bios.bin ROCKNIX declares settles it.
EmuDeck passes Complex_4627v1.03.bin as xemu's flash ROM
(emuDeckXemu.sh:60-61), and xemu's entry Complex_4627.bin states no hash,
only the sizes it maps. The layer matched entries by name or content
only, so without the alias the default name was still asked for. A
hashless entry that checks a size now takes a launcher file of a size
it accepts, when no other entry of that core accepts that size too.
The launcher layer packed a file under the launcher's name whatever the
platform installs: ROCKNIX's xemu config reads hdd/xbox_hdd.qcow2, and
the profile marks that image installed_on rocknix, yet the pack brought
one. A place whose entry the emulator installs on that platform is now
filled by the install, as validation.deliverable has it for the pack.
A names_searched list is one place the launcher fills with the first name it finds, so a core file it would never open once another name of the list is held is not reported missing. A place no declared file and no packed core file fills receives, under the launcher's name, a file the core accepts by content. The layer is applied inside find_undeclared_files, which verify and the pack builder both read, and a test reads their source to keep it there.
Abdessamad Derraz