diff --git a/.github/workflows/nix-check.yml b/.github/workflows/nix-check.yml
new file mode 100644
index 00000000000..7071f849837
--- /dev/null
+++ b/.github/workflows/nix-check.yml
@@ -0,0 +1,49 @@
+name: Nix Flake Check
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+      - 'release-*'
+      - 'dev-*'
+permissions:
+  contents: read
+
+jobs:
+  flake-check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@v9
+
+      - name: Enable flakes
+        uses: DeterminateSystems/magic-nix-cache-action@v2
+
+      - name: Check Nix flake inputs
+        run: nix flake check
+
+      - name: Show flake metadata
+        if: always() # Run even if previous step fails
+        run: nix flake metadata
+
+      - name: Validate flake outputs
+        if: always() # Run even if previous step fails
+        run: nix flake show
+
+      - name: Check build in Nix dev shell
+        run: |
+          # Enter nix develop and run build commands
+          nix develop --command bash -c '
+            # Install dependencies
+            yarn install
+            
+            # Build the project
+            yarn build
+            
+            # Build cosmic-swingset
+            cd packages/cosmic-swingset && make
+          '
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 00000000000..1d23a9ef874
--- /dev/null
+++ b/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": 1739446958,
+        "narHash": "sha256-+/bYK3DbPxMIvSL4zArkMX0LQvS7rzBKXnDXLfKyRVc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "2ff53fe64443980e139eaa286017f53f88336dd0",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-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
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 00000000000..0946fd371f7
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,75 @@
+{
+  description = "Agoric SDK Development Environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+               # Custom Node.js 20.9.0 package
+        custom_node_20_9 = pkgs.stdenv.mkDerivation {
+          pname = "nodejs";
+          version = "20.9.0";
+          
+          src = pkgs.fetchurl {
+            url = "https://nodejs.org/dist/v20.9.0/node-v20.9.0-${if pkgs.stdenv.isDarwin then "darwin" else "linux"}-${if pkgs.stdenv.isAarch64 then "arm64" else "x64"}.tar.gz";
+            sha256 = if pkgs.stdenv.isDarwin && pkgs.stdenv.isAarch64 then
+              "0snfsz2mmjdavi38nglayw5yia74q9h1xzz2ahpri8yqx1md9lii" # darwin-arm64
+            else if pkgs.stdenv.isDarwin then
+              "1j6cw6i3hjqv8zk1nbsqg560k7rgcmyl9cfd4vlvn5wclzr76nzw" # darwin-x64
+            else if pkgs.stdenv.isAarch64 then
+              "0skah3bal5irvramnfn86vgi0c375ywsyb4xaxmx3gvlnbpdp9yj" # linux-arm64
+            else if (pkgs.stdenv.isLinux && !pkgs.stdenv.isAarch64) then
+              "0q3gy4z5b8dd0w37ya5wlkbv4xhyqa1s0zwh71258x5z5w4rz4gh" # linux-x64
+            else
+              throw "Unsupported system: This derivation only supports Linux (x64/arm64) and Darwin (x64/arm64) systems";
+          };
+
+          installPhase = ''
+              echo "installing nodejs"
+              mkdir -p $out
+              cp -r ./ $out/
+            '';
+
+
+          # Meta information for the package
+          meta = with pkgs.lib; {
+            description = "Node.js 20.9.0 JavaScript runtime";
+            homepage = "https://nodejs.org";
+            license = licenses.mit;
+            platforms = platforms.unix;
+          };
+        };
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          buildInputs = with pkgs; [
+            custom_node_20_9
+            (yarn.override { nodejs = custom_node_20_9; })
+            (python3.withPackages (ps: [ ps.distutils ]))
+            pkg-config
+            go_1_23
+            gopls
+            delve
+            gcc
+            gnumake
+            protobuf
+            buf
+            git
+          ];
+
+          shellHook = ''
+            export PATH=$PATH:$HOME/go/bin
+
+            echo "Node.js $(node --version)"
+            echo "NPM $(npm --version)"
+            echo "Yarn using Node.js $(yarn node -v)"
+          '';
+        };
+      }
+    );
+}
diff --git a/patches/ava+5.3.1.patch b/patches/ava+5.3.1.patch
index f3ccc74b2c5..98a788fbaf2 100644
--- a/patches/ava+5.3.1.patch
+++ b/patches/ava+5.3.1.patch
@@ -94,38 +94,6 @@ index 7630baa..78ced77 100644
  
  		notifyOfPeerFailure() {
  			send({type: 'peer-failed'});
-diff --git a/node_modules/ava/lib/reporters/tap.js b/node_modules/ava/lib/reporters/tap.js
-index b1989a4..fa1617f 100644
---- a/node_modules/ava/lib/reporters/tap.js
-+++ b/node_modules/ava/lib/reporters/tap.js
-@@ -45,6 +45,10 @@ function dumpError(error) {
- 	return object;
- }
- 
-+function durationOut(dur) {
-+	return dur ? ` %ava-dur=${dur}ms` : '';
-+}
-+
- export default class TapReporter {
- 	constructor(options) {
- 		this.i = 0;
-@@ -96,6 +100,7 @@ export default class TapReporter {
- 	}
- 
- 	writeTest(evt, flags) {
-+ 		evt.title += durationOut(evt.duration);
- 		this.reportStream.write(supertap.test(this.prefixTitle(evt.testFile, evt.title), {
- 			comment: evt.logs,
- 			error: evt.err ? dumpError(evt.err) : null,
-@@ -108,7 +113,7 @@ export default class TapReporter {
- 
- 	writeCrash(evt, title) {
- 		this.crashCount++;
--		this.reportStream.write(supertap.test(title || evt.err.summary || evt.type, {
-+		this.reportStream.write(supertap.test((title || evt.err.summary || evt.type) + durationOut(evt.duration), {
- 			comment: evt.logs,
- 			error: evt.err ? dumpError(evt.err) : null,
- 			index: ++this.i,
 diff --git a/node_modules/ava/lib/worker/base.js b/node_modules/ava/lib/worker/base.js
 index cdd3c4a..4302a4a 100644
 --- a/node_modules/ava/lib/worker/base.js