Enable SQLite extension loading in devshell (#48)

Override sqlite in devShell to enable extension loading for sqlite-vec
support when running tests. Only sets BREW_PREFIX if not already defined
to avoid overriding user's existing setup.

Package build remains unchanged.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

flake.lock

@@ -0,0 +1,61 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1769188852,
+        "narHash": "sha256-aBAGyMum27K7cP5OR7BMioJOF3icquJMZDDgk6ZEg1A=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a1bab9e494f5f4939442a57a58d0449a109593fe",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -11,6 +11,13 @@
       let
         pkgs = nixpkgs.legacyPackages.${system};
 
+        # SQLite with loadable extension support for sqlite-vec
+        sqliteWithExtensions = pkgs.sqlite.overrideAttrs (old: {
+          configureFlags = (old.configureFlags or []) ++ [
+            "--enable-load-extension"
+          ];
+        });
+
         qmd = pkgs.stdenv.mkDerivation {
           pname = "qmd";
           version = "1.0.0";
@@ -62,10 +69,11 @@
         devShells.default = pkgs.mkShell {
           buildInputs = [
             pkgs.bun
-            pkgs.sqlite
+            sqliteWithExtensions
           ];
 
           shellHook = ''
+            export BREW_PREFIX="''${BREW_PREFIX:-${sqliteWithExtensions.out}}"
             echo "QMD development shell"
             echo "Run: bun src/qmd.ts <command>"
           '';