cargo fmt -all

flake.nix

@@ -123,13 +123,13 @@
 
           # Put the GUI shared libraries on the runtime library path so winit
           # can dlopen libwayland and wgpu can find the vulkan loader.
-          shellHook =
-            ''
-              export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:${pkgs.lib.makeLibraryPath guiLibs}"
-            ''
-            + pkgs.lib.optionalString pkgs.stdenv.hostPlatform.isLinux ''
-              export RUSTFLAGS="-C link-arg=-fuse-ld=mold"
-            '';
+          # No RUSTFLAGS here: an env RUSTFLAGS would override (not merge
+          # with) ~/.cargo/config.toml's rustflags, giving devShell and
+          # non-devShell builds different fingerprints and force-rebuilding
+          # every dependency on each switch.
+          shellHook = ''
+            export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:${pkgs.lib.makeLibraryPath guiLibs}"
+          '';
 
           # Extra inputs can be added here; cargo and rustc are provided by default.
           packages = guiLibs ++ pkgs.lib.optionals pkgs.stdenv.hostPlatform.isLinux [ pkgs.mold ];