diff --git a/README.md b/README.md
index 500e7c7..e7e11e0 100644
--- a/README.md
+++ b/README.md
@@ -6,20 +6,16 @@ Dark charcoal shell, accent-blue arcs, auto-scaling ceilings, and a per-device b
 
 ## Run
 
-```bash
-nix run                 # apps.default → usage (Nix-packaged binary)
-nix run .#usage
-```
-
-### Build with the devshell toolchain (no remote builders)
-
 From this checkout (with sibling `../vidya`):
 
 ```bash
-nix run .#build         # cargo build --release (rustc/cargo from flake)
-./target/release/usage
+nix run                 # apps.default → cargo build --release && run
+nix run .#usage         # same
+nix run .#build         # cargo build --release only
 ```
 
+`apps.usage` / `apps.default` use the **devshell toolchain** (`rustc`/`cargo` + egui libs) in the working tree — no pure sandbox, no remote builders. Incremental builds go into `./target/`.
+
 Optional interactive shell:
 
 ```bash
@@ -27,6 +23,13 @@ nix develop
 cargo run --release
 ```
 
+Packaged install (pure Nix derivation — may use remote builders):
+
+```bash
+nix build .#usage
+./result/bin/usage
+```
+
 ## What you see
 
 | Gauge | Source |
@@ -49,12 +52,12 @@ Below the gauges: cards listing individual disks and network interfaces with min
 
 | Output | Role |
 |--------|------|
-| `apps.default` / `apps.usage` | Launch the window (packaged derivation) |
-| `apps.build` | `cargo build --release` via devshell tools (local, no sandbox) |
-| `packages.default` / `packages.usage` | Wrapped binary (`LD_LIBRARY_PATH` for GL/Wayland) |
+| `apps.default` / `apps.usage` | Devshell: `cargo build --release` then run |
+| `apps.build` | Devshell: `cargo build --release` only |
+| `packages.default` / `packages.usage` | Pure packaged binary (`nix build`) |
 | `devShells.default` | rustc + cargo + egui runtime libs |
 
-Flake input `vidya` is staged beside the crate so `path = "../vidya"` resolves under `nix build` / `nix run`.
+Apps need a live checkout next to `../vidya`. The packaged `packages.usage` stages flake input `vidya` for pure builds.
 
 ## License
 
diff --git a/flake.nix b/flake.nix
index 5e6ae97..931adeb 100644
--- a/flake.nix
+++ b/flake.nix
@@ -33,6 +33,26 @@
           libxi
           libxrandr
         ];
+
+      # Shared by apps.build / apps.usage: enter checkout + set link path.
+      cargoPreamble = libPath: ''
+        set -euo pipefail
+        export LD_LIBRARY_PATH="${libPath}''${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"
+
+        if [ ! -f Cargo.toml ] && [ -f "''${FLAKE_ROOT:-}/Cargo.toml" ]; then
+          cd "$FLAKE_ROOT"
+        fi
+        if [ ! -f Cargo.toml ]; then
+          echo "usage: no Cargo.toml here (cwd=$PWD)" >&2
+          echo "  cd into the usage checkout, then: nix run .#usage" >&2
+          exit 1
+        fi
+        if [ ! -d ../vidya ]; then
+          echo "usage: expected sibling ../vidya (Cargo path dep)" >&2
+          echo "  clone vidya next to usage, or: nix build .#usage" >&2
+          exit 1
+        fi
+      '';
     in
     {
       packages = forAllSystems (
@@ -42,7 +62,8 @@
           inherit (pkgs) lib;
           libs = eguiLibs pkgs;
 
-          # Cargo.toml expects path = "../vidya" (sibling of the package root).
+          # Packaged binary for `nix build` / install — pure, remote-builder capable.
+          # Day-to-day: prefer `nix run .#usage` (devshell cargo path below).
           srcTree = pkgs.runCommand "usage-src" { } ''
             mkdir -p $out/usage $out/vidya
             cp -a ${lib.cleanSource ./.}/. $out/usage/
@@ -89,53 +110,45 @@
           inherit (pkgs) lib;
           libs = eguiLibs pkgs;
           libPath = lib.makeLibraryPath libs;
-          pkg = self.packages.${system}.usage;
+          cargoTools = with pkgs; [
+            rustc
+            cargo
+            pkg-config
+          ];
 
-          # Local cargo build with the same toolchain/libs as devShells.default.
-          # Avoids remote builders / pure sandbox — run from the checkout:
-          #   nix run .#build
+          # Local cargo build (devshell tools; no pure sandbox / remote upload lock).
           build = pkgs.writeShellApplication {
             name = "usage-build";
-            runtimeInputs = with pkgs; [
-              rustc
-              cargo
-              pkg-config
-            ];
+            runtimeInputs = cargoTools;
             text = ''
-              set -euo pipefail
-              export LD_LIBRARY_PATH="${libPath}''${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"
-
-              # Prefer the flake checkout when invoked as `nix run .#build` from elsewhere.
-              if [ ! -f Cargo.toml ] && [ -f "''${FLAKE_ROOT:-}/Cargo.toml" ]; then
-                cd "$FLAKE_ROOT"
-              fi
-              if [ ! -f Cargo.toml ]; then
-                echo "usage-build: no Cargo.toml here (cwd=$PWD)" >&2
-                echo "  cd into the usage checkout, then: nix run .#build" >&2
-                exit 1
-              fi
-              if [ ! -d ../vidya ]; then
-                echo "usage-build: expected sibling ../vidya (Cargo path dep)" >&2
-                echo "  clone vidya next to usage, or use: nix build .#usage" >&2
-                exit 1
-              fi
-
+              ${cargoPreamble libPath}
               echo "→ cargo build --release $*"
               cargo build --release "$@"
               echo "✓ target/release/usage"
-              echo "  run:  LD_LIBRARY_PATH=${libPath}:\''${LD_LIBRARY_PATH:-} ./target/release/usage"
-              echo "  or:   nix develop -c cargo run --release"
+            '';
+          };
+
+          # Build (if needed) and run via the same toolchain as `nix develop`.
+          usageApp = pkgs.writeShellApplication {
+            name = "usage";
+            runtimeInputs = cargoTools;
+            text = ''
+              ${cargoPreamble libPath}
+              echo "→ cargo build --release"
+              cargo build --release
+              echo "→ target/release/usage $*"
+              exec ./target/release/usage "$@"
             '';
           };
         in
         {
           default = {
             type = "app";
-            program = "${pkg}/bin/usage";
+            program = "${usageApp}/bin/usage";
           };
           usage = {
             type = "app";
-            program = "${pkg}/bin/usage";
+            program = "${usageApp}/bin/usage";
           };
           build = {
             type = "app";
@@ -162,7 +175,7 @@
             buildInputs = libs;
             LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath libs;
             shellHook = ''
-              echo "usage — cargo run | nix run .#build | nix run"
+              echo "usage — nix run | nix run .#build | nix develop"
             '';
           };
         }