Configure devenv to build output

devenv.nix

@@ -6,6 +6,30 @@
   ...
 }:
 
+let
+  # devenv's `languages.rust.import` only builds single root-package crates
+  # (it hardcodes `cargoNix.rootCrate.build`). tora is a virtual workspace with
+  # no root package, so we drive crate2nix directly and select the `torad` member
+  # out of `workspaceMembers`. src = ./. gives crate2nix the whole workspace, so
+  # torad's path-dependency on ../proto (tora-proto) resolves.
+  crate2nixTools = pkgs.callPackage "${inputs.crate2nix}/tools.nix" { };
+  cargoNix =
+    pkgs.callPackage
+      (crate2nixTools.generatedCargoNix {
+        name = "tora";
+        src = ./.;
+      })
+      {
+        # Build with the toolchain configured for this dev environment,
+        # matching what languages.rust.import does internally.
+        buildRustCrateForPkgs =
+          _:
+          pkgs.buildRustCrate.override {
+            rustc = config.languages.rust.toolchainPackage;
+            cargo = config.languages.rust.toolchainPackage;
+          };
+      };
+in
 {
   languages.rust.enable = true;
   git-hooks.hooks = {
@@ -57,13 +81,13 @@
 
   processes.torad = {
     exec = ''
-      cargo run -p torad -- --socket "$TORAD_SOCKET" --pid-file "$TORAD_PID_FILE"
+      ${config.outputs.torad}/bin/torad --socket "$TORAD_SOCKET" --pid-file "$TORAD_PID_FILE"
     '';
     # Waits for postgres's own readiness probe (pg_isready + SELECT 1), not just process start.
     after = [ "devenv:processes:postgres" ];
   };
 
   outputs = {
-    tora = config.languages.rust.import ./. { };
+    torad = cargoNix.workspaceMembers.torad.build;
   };
 }