Use commit time not build time

Can't use build time in pure evaluation mode.

default.nix

@@ -1,31 +1,41 @@
 { pkgs ? import <nixpkgs> { }, proj ? pkgs.proj }:
 
+let
+  # Get commit timestamp at eval time (pure)
+  getCommitTime = 
+    if builtins.pathExists ./.git
+    then builtins.replaceStrings ["\n"] [""] (builtins.readFile (
+      pkgs.runCommand "git-commit-time" {} ''
+        ${pkgs.git}/bin/git -C ${./.} log -1 --format=%ct > $out
+      ''
+    ))
+    else "0";
+in
 pkgs.buildGoModule rec {
-  buildTime = builtins.currentTime;
+  pname = "nidus-sync";
-  # Try to get git info, fallback to version if .git doesn't exist
+  version = "0.0.12";
-  # Note: This runs at eval time, so it captures the version when you build
+  src = ./.;
+  
   gitRevision = 
     if builtins.pathExists ./.git 
     then pkgs.lib.commitIdFromGitRepo ./.git 
     else "unknown";
-  gitDescribe = builtins.readFile (pkgs.runCommand "git-describe" {} ''
+  
-    ${pkgs.git}/bin/git -C ${./.} describe --always --dirty --tags 2>/dev/null > $out || echo "${version}" > $out
+  buildTime = getCommitTime;
-  '');
+  
   ldflags = [
     "-s"
     "-w"
     "-X main.Version=${version}"
     "-X main.Commit=${gitRevision}"
-    "-X main.BuildTime=${toString buildTime}"
+    "-X main.BuildTime=${buildTime}"
   ];
   meta = {
     description = "Nidus Sync";
     homepage = "https://github.com/Gleipnir-Technology/nidus-sync";
   };
-  pname = "nidus-sync";
+  
-  src = ./.;
   subPackages = [];
-  version = "0.0.12";
   vendorHash = "sha256-jlPS8lWdNPj60BMUcCrxteLuc7RXEXDtzlwjsFBJg0Y=";
 
   buildInputs = [ pkgs.proj ];