chore: scaffold dev-env module (options + config + lib stubs)

default.nix composes the three sub-modules. options.nix declares the
public surface (projects, regtest, fakewallet, tmux) so consumers can
wire values today even though config.nix is empty. lib.nix reserves
dev-env-scoped helpers separate from the global lnbits-sensei.lib.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

modules/dev-env/options.nix

@@ -0,0 +1,161 @@
+# lnbits-sensei dev-env — option schema.
+#
+# Skeleton-only. Declares the option surface so consumers can wire
+# values today and the substantive implementation can land later
+# without churning the public API.
+{ config, lib, ... }:
+
+let
+  inherit (lib) mkEnableOption mkOption types;
+
+  # One entry in dev-env.projects. A project is a git repo with one or
+  # more worktrees (or a single clone if `isClone = true`). Worktrees
+  # are derived from a bare repo at `${dev-env.root}/repos/<name>.git`
+  # by default.
+  projectType = types.submodule (
+    { name, ... }:
+    {
+      options = {
+        url = mkOption {
+          type = types.nullOr types.str;
+          default = null;
+          description = ''
+            Origin URL for this project. May be an upstream URL, a
+            personal fork, or a private mirror — the dev-env bootstrap
+            script reconciles the rest of the remote topology from
+            `lnbits-sensei.git.remotes`.
+          '';
+          example = "https://github.com/lnbits/lnbits";
+        };
+
+        worktrees = mkOption {
+          type = types.attrsOf (
+            types.submodule {
+              options = {
+                branch = mkOption {
+                  type = types.str;
+                  description = "Branch to check out in this worktree.";
+                };
+              };
+            }
+          );
+          default = { };
+          description = ''
+            Worktrees to materialize for this project, keyed by
+            worktree name. Each becomes a directory under the project
+            root.
+          '';
+          example = lib.literalExpression ''
+            {
+              main = { branch = "main"; };
+              dev  = { branch = "dev"; };
+            }
+          '';
+        };
+
+        isClone = mkEnableOption ''
+          Treat as a plain clone rather than a bare-repo + worktrees
+          set. Use for projects you won't have multiple simultaneous
+          branches checked out for
+        '';
+      };
+    }
+  );
+
+  # One entry in dev-env.tmux.sessions. Mirrors the omnixy shape so
+  # the `dev-tm <name>` launcher can ship later with a familiar API.
+  tmuxSessionType = types.submodule {
+    options = {
+      cwd = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        description = "Session-default cwd, relative to dev-env.root.";
+      };
+      windows = mkOption {
+        type = types.listOf (
+          types.submodule {
+            options = {
+              name = mkOption { type = types.str; };
+              cwd = mkOption {
+                type = types.nullOr types.str;
+                default = null;
+              };
+              cmd = mkOption {
+                type = types.nullOr types.str;
+                default = null;
+                description = "Command to run in the window on creation.";
+              };
+            };
+          }
+        );
+        default = [ ];
+      };
+    };
+  };
+in
+{
+  options.lnbits-sensei.devEnv = {
+    enable = mkEnableOption "lnbits-sensei dev-env tooling";
+
+    root = mkOption {
+      type = types.str;
+      default = "/home/${config.lnbits-sensei.user or "user"}/dev";
+      defaultText = "/home/\${config.lnbits-sensei.user}/dev";
+      description = ''
+        Root directory for the dev environment. Worktrees and project
+        clones live under this prefix; bare repos under
+        `''${root}/repos/`.
+      '';
+    };
+
+    projects = mkOption {
+      type = types.attrsOf projectType;
+      default = { };
+      description = ''
+        Hand-authored project list. Consumed by the bootstrap script
+        (later pass) to materialize repos and worktrees on disk.
+      '';
+    };
+
+    regtest = {
+      enable = mkEnableOption ''
+        Bitcoin/Lightning regtest docker stack. Wraps an upstream
+        fork of `lnbits/legend-regtest-enviroment` (LND + CLN +
+        Eclair + bitcoind + electrs). Implies a container engine —
+        the substantive pass will gate this on a containers feature
+      '';
+
+      repoUrl = mkOption {
+        type = types.str;
+        default = "https://github.com/lnbits/legend-regtest-enviroment";
+        description = ''
+          Git URL of the regtest docker-compose repo. Cloned by the
+          dev-env bootstrap script. Point at your own fork if you've
+          customised the stack.
+        '';
+      };
+    };
+
+    fakewallet = {
+      enable = mkEnableOption ''
+        FakeWallet dev mode helpers. Installs the symmetric `fakewallet`
+        wrapper script (a no-op for parity with `regtest up`) so the
+        dev experience is identical whether you're on the default
+        FakeWallet path or the full regtest stack
+      '';
+    };
+
+    tmux = {
+      enable = mkEnableOption "declarative tmux session launcher";
+
+      sessions = mkOption {
+        type = types.attrsOf tmuxSessionType;
+        default = { };
+        description = ''
+          Named tmux session layouts. The launcher script (later pass)
+          reads these at runtime and recreates the session.
+        '';
+      };
+    };
+  };
+}