assembleMappings
Cross into the masking loader (mapping-io + tiny-remapper live only there) to assemble the remap mappings: the half of the bundle that depends on the MC version alone. Called by RemapCache on a non-mojmap runtime with no mcp.remap.* flags, when no mappings are cached for this version yet.
Parameters
path to the Mojang client mappings (client.txt)
the runtime names clientTxt cannot supply — told apart by extension. MCPConfig's joined.tsrg (obf → srg, forge), spigot BuildData's bukkit-<ver>-cl.csrg, or the fabric intermediary MAPPINGS jar (net.fabricmc:intermediary:<ver>:v2), read for its mappings/mappings.tiny. Never a Minecraft jar: that one is buildSymbols's.
output path for the assembled mappings: .tsrg on forge, .tiny otherwise
Throws
if masking-loader init or assembly fails