ci: sneak a flake in

Author: willcl-ark

ci/flake.lock

@@ -0,0 +1,53 @@
+{
+  description = "Bitcoin Core development environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = {
+    nixpkgs,
+    flake-utils,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem (
+      system: let
+        pkgs = import nixpkgs {
+          inherit system;
+        };
+      in {
+        formatter = pkgs.alejandra;
+
+        devShells.default = pkgs.mkShell.override {
+          stdenv = pkgs.gcc15Stdenv;
+        } {
+          buildInputs = with pkgs; [
+            ccache
+            cmake
+            ninja
+            pkg-config
+
+            boost
+            capnproto
+            libevent
+            libsystemtap
+            linuxPackages.bcc
+            linuxPackages.bpftrace
+            sqlite.dev
+            zeromq
+          ];
+
+          shellHook = ''
+            export CCACHE_COMPRESS=1
+            export CCACHE_SLOPPINESS=random_seed
+            export CCACHE_UMASK=007
+            export CMAKE_GENERATOR=Ninja
+
+            echo "CCACHE_DIR: $CCACHE_DIR"
+          '';
+        };
+      }
+    );
+}
+