Depending on the $pwd, I guess something like this:

nix-build -E '((import <nixpkgs> {}).callPackage ./modules/nbitcoin/default.nix {}).fetch-deps

Depending on the $pwd, I guess something like this:

nix-build -E '((import <nixpkgs> {}).callPackage ./modules/nbitcoin/default.nix {}).fetch-deps

$ echo $dotnetProjectFiles
/nix/store/85fkamr6na3xjznqa70hasdzrlxqgbrr-NBitcoin.CppBridge.csproj

This shouldn't be a store path.

diff --git a/modules/nbitcoin/default.nix b/modules/nbitcoin/default.nix
index 2342c8e..bb38b51 100644
--- a/modules/nbitcoin/default.nix
+++ b/modules/nbitcoin/default.nix
@@ -32,7 +32,7 @@ buildDotnetModule rec {
     fileset = sourceFiles;
   };
   sourceRoot = "${src.name}/modules/nbitcoin";
-  projectFile = ./NBitcoin.CppBridge.csproj;
+  projectFile = "NBitcoin.CppBridge.csproj";
 
   nugetDeps = ./deps.json;
 

Yeah, about that:

Finished dotnetConfigureHook
/nix/store/qmvcsvn9dw5v7cln85ay8pydir38ab43-fetch-deps.sh: line 10: /nix/store/dxv3prj2zy34n0inhhznihnhww2gfnfd-source/modules/nbitcoin/deps.json: Read-only file system

How does one do that?

I don't understand what dotnet restore is trying to do though. If it's unable to restore on a read-only tree, why is it blowing up the system?

(though ive also never had the fetch-deps script work without having to explicitly pass the path to the output deps file, because it tries writing into the store by default...)

Yeah, I had to do that too