Add base Nix/Flake setup

crates/geomerge-demo/README.md

@@ -12,12 +12,6 @@ The demo:
 
 ![Workflow Diagram](docs/diagrams/workflow.svg)
 
-The SVG is generated from `docs/diagrams/workflow.dot`. To regenerate it after editing the `.dot` source, run:
-
-```sh
-bash docs/diagrams/make_figures.sh docs/diagrams
-```
-
 ### Run
 
 ```sh

flake.lock

@@ -0,0 +1,82 @@
+{
+  "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": 1779560665,
+        "narHash": "sha256-tpyBcxPpcQb8ukyNF7DoCwfSY3VPsxHoYwj00Cayv5o=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "64c08a7ca051951c8eae34e3e3cb1e202fe36786",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs",
+        "rust-overlay": "rust-overlay"
+      }
+    },
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1780024773,
+        "narHash": "sha256-aU9nlrS9S+IJ2EiCzsaxzOXUhggogqTrJojBicE6Oeg=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "40b0a3a193e0840c76174b4a322874c8f6dd0a63",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
+      }
+    },
+    "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

@@ -0,0 +1,56 @@
+{
+  description = "Storage engine playground: Rust workspace for FlowLog, DBSP, CRDT, and Geomerge experiments.";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = { self, nixpkgs, flake-utils, rust-overlay }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          overlays = [ rust-overlay.overlays.default ];
+        };
+
+        # Edition 2024 requires Rust >= 1.85. Pin to a recent stable.
+        rustToolchain = pkgs.rust-bin.stable.latest.default.override {
+          extensions = [ "rust-src" "rust-analyzer" "clippy" "rustfmt" ];
+        };
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          name = "storage-engine-playground";
+
+          packages = [
+            rustToolchain
+            # Diagram regeneration in crates/geomerge-demo/docs/diagrams.
+            pkgs.graphviz
+            # Cargo helpers.
+            pkgs.cargo-watch
+            pkgs.cargo-nextest
+            # Pre-commit hooks (see .pre-commit-config.yaml, Makefile setup-hooks).
+            pkgs.pre-commit
+            pkgs.python3
+          ];
+
+          env = {
+            RUST_BACKTRACE = "1";
+          };
+
+          shellHook = ''
+            echo "storage-engine-playground dev shell"
+            echo "  rustc: $(rustc --version)"
+            echo "  cargo: $(cargo --version)"
+            echo "  dot:   $(dot -V 2>&1)"
+          '';
+        };
+
+        formatter = pkgs.nixpkgs-fmt;
+      });
+}