diff --git a/.github/workflows/voltage-buzz-gpui-release.yml b/.github/workflows/voltage-buzz-gpui-release.yml
index c4899a3f41a..96a9fc0714d 100644
--- a/.github/workflows/voltage-buzz-gpui-release.yml
+++ b/.github/workflows/voltage-buzz-gpui-release.yml
@@ -17,6 +17,10 @@ on:
       - .github/workflows/voltage-buzz-gpui-release.yml
       - apps/buzz-gpui/.github/actions/**
       - apps/buzz-gpui/scripts/package-*
+      - apps/buzz-gpui/scripts/build-package.sh
+      - apps/buzz-gpui/scripts/check-remote-provider.mjs
+      - apps/buzz-gpui/scripts/check-remote-provider.test.mjs
+      - apps/buzz-gpui/scripts/test-package-build.py
       - apps/buzz-gpui/scripts/bundle-macos-*
       - apps/buzz-gpui/scripts/check-macos-*
 
@@ -27,7 +31,22 @@ concurrency:
 permissions:
   contents: read
 
+env:
+  # Ship the Remote workspace UI and its provider on every desktop platform.
+  BUZZ_GPUI_VOLTAGE: "1"
+
 jobs:
+  package-contract:
+    name: Desktop package contract
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+        with:
+          persist-credentials: false
+      - run: python3 apps/buzz-gpui/scripts/test-package-build.py
+      - run: node --test apps/buzz-gpui/scripts/check-remote-provider.test.mjs
+
   version:
     name: GPUI release version
     runs-on: ubuntu-latest
@@ -61,7 +80,7 @@ jobs:
 
   linux:
     name: GPUI Linux x86_64 (.deb)
-    needs: version
+    needs: [version, package-contract]
     runs-on: ubuntu-latest
     timeout-minutes: 120
     env:
@@ -81,7 +100,7 @@ jobs:
 
   macos:
     name: GPUI macOS ${{ matrix.arch }} (.dmg)
-    needs: version
+    needs: [version, package-contract]
     runs-on: ${{ matrix.runner }}
     timeout-minutes: 120
     strategy:
@@ -128,7 +147,7 @@ jobs:
 
   windows:
     name: GPUI Windows x86_64 (.zip)
-    needs: version
+    needs: [version, package-contract]
     runs-on: windows-latest
     timeout-minutes: 120
     env:
@@ -148,7 +167,7 @@ jobs:
         with:
           workspaces: apps/buzz-gpui
           save-if: ${{ github.ref == 'refs/heads/main' }}
-      - run: cargo build --locked --release -p buzz-gpui -p buzzd
+      - run: bash scripts/build-package.sh -p buzzd
         working-directory: apps/buzz-gpui
       - run: |
           python -m pip install pefile
@@ -157,6 +176,8 @@ jobs:
       # The bundled Node runs every bundled plugin.
       - run: dist/Buzz/lib/buzz-gpui/node/bin/node.exe scripts/check-plugins.mjs dist/Buzz/share/buzz-gpui/plugins
         working-directory: apps/buzz-gpui
+      - run: dist/Buzz/lib/buzz-gpui/node/bin/node.exe scripts/check-remote-provider.mjs dist/Buzz/bin/buzz-backend-relay.exe
+        working-directory: apps/buzz-gpui
       - uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7
         with:
           name: buzz-gpui-windows-x86_64
diff --git a/apps/buzz-gpui/README.md b/apps/buzz-gpui/README.md
index 37b32ce2833..78506feb307 100644
--- a/apps/buzz-gpui/README.md
+++ b/apps/buzz-gpui/README.md
@@ -91,6 +91,12 @@ The ones you may notice:
 
 ### Builds
 
+Voltage's release workflow sets `BUZZ_GPUI_VOLTAGE=1`. These packages enable
+Remote workspaces and place `buzz-backend-relay` beside the app executable.
+The package checks run the bundled provider's credential-free `info` operation.
+For a local Voltage package, set this variable before running its package script.
+On Windows, build first with `bash scripts/build-package.sh -p buzzd`.
+
 The Build workflow makes all of these packages. It runs by hand, for pull
 requests that change it, and for `v*` tags, which also attach the packages
 to a GitHub release.
diff --git a/apps/buzz-gpui/crates/app/Cargo.toml b/apps/buzz-gpui/crates/app/Cargo.toml
index be0c2997f2d..5863296f6cb 100644
--- a/apps/buzz-gpui/crates/app/Cargo.toml
+++ b/apps/buzz-gpui/crates/app/Cargo.toml
@@ -148,3 +148,10 @@ assets = [
     ["target/release/bundle/node/LICENSE", "usr/lib/buzz-gpui/node/", "644"],
     ["target/release/bundle/plugins/**/*", "usr/share/buzz-gpui/plugins/", "644"],
 ]
+
+[package.metadata.deb.variants.voltage]
+name = "buzz-gpui"
+features = ["voltage-sandbox"]
+merge-assets.append = [
+    ["target/release/buzz-backend-relay", "usr/bin/buzz-backend-relay", "755"],
+]
diff --git a/apps/buzz-gpui/scripts/build-package.sh b/apps/buzz-gpui/scripts/build-package.sh
new file mode 100644
index 00000000000..618efce1e00
--- /dev/null
+++ b/apps/buzz-gpui/scripts/build-package.sh
@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+# Build the package's app, and Voltage's provider beside it when requested.
+set -euo pipefail
+here="$(cd "$(dirname "$0")/.." && pwd)"
+repo="$(cd "$here/../.." && pwd)"
+cd "$here"
+target="${CARGO_TARGET_DIR:-$here/target}"
+features=()
+if [ "${BUZZ_GPUI_VOLTAGE:-0}" = 1 ]; then
+  features=(--features voltage-sandbox)
+  cargo build --manifest-path "$repo/Cargo.toml" --locked --release \
+    -p buzz-backend-relay --target-dir "$target/voltage-provider"
+fi
+cargo build --locked --release -p buzz-gpui "${features[@]}" "$@"
+if [ "${BUZZ_GPUI_VOLTAGE:-0}" = 1 ]; then
+  suffix=""
+  if [ "${OS:-}" = Windows_NT ]; then suffix=.exe; fi
+  cp "$target/voltage-provider/release/buzz-backend-relay$suffix" "$target/release/"
+fi
diff --git a/apps/buzz-gpui/scripts/check-macos-dmg.sh b/apps/buzz-gpui/scripts/check-macos-dmg.sh
index f6a2abc0cd4..fd313c52944 100755
--- a/apps/buzz-gpui/scripts/check-macos-dmg.sh
+++ b/apps/buzz-gpui/scripts/check-macos-dmg.sh
@@ -42,6 +42,10 @@ app="$work/Buzz.app"
 # The bundled Node runs every bundled plugin.
 "$app/Contents/Resources/node/bin/node" "$here/scripts/check-plugins.mjs" \
   "$app/Contents/Resources/plugins"
+if [ "${BUZZ_GPUI_VOLTAGE:-0}" = 1 ]; then
+  "$app/Contents/Resources/node/bin/node" "$here/scripts/check-remote-provider.mjs" \
+    "$app/Contents/MacOS/buzz-backend-relay"
+fi
 du -sh "$app"
 codesign --verify --deep --strict "$app"
 
diff --git a/apps/buzz-gpui/scripts/check-remote-provider.mjs b/apps/buzz-gpui/scripts/check-remote-provider.mjs
new file mode 100644
index 00000000000..28454d1b5c3
--- /dev/null
+++ b/apps/buzz-gpui/scripts/check-remote-provider.mjs
@@ -0,0 +1,23 @@
+// Exercise the packaged provider without credentials or a relay connection.
+import { spawnSync } from "node:child_process";
+
+const binary = process.argv[2];
+if (!binary) throw new Error("Expected the packaged buzz-backend-relay path");
+const result = spawnSync(binary, {
+  input: '{"op":"info"}\n',
+  encoding: "utf8",
+  timeout: 10_000,
+  maxBuffer: 64 * 1024,
+});
+if (result.error || result.status !== 0) {
+  throw new Error("The packaged relay provider could not start");
+}
+const info = JSON.parse(result.stdout);
+const nonemptyText = (field) => typeof info?.[field] === "string" && info[field].length > 0;
+if (info?.ok !== true || info.name !== "relay" || info.protocol_version !== 1 ||
+    !nonemptyText("version") || !nonemptyText("description") ||
+    !info.config_schema || typeof info.config_schema !== "object" || Array.isArray(info.config_schema) ||
+    !Array.isArray(info.ops) || !["deploy", "stop", "recover"].every((op) => info.ops.includes(op))) {
+  throw new Error("The packaged relay provider has an incompatible protocol");
+}
+console.log("Packaged relay provider supports deploy, stop, and recovery");
diff --git a/apps/buzz-gpui/scripts/check-remote-provider.test.mjs b/apps/buzz-gpui/scripts/check-remote-provider.test.mjs
new file mode 100644
index 00000000000..af2aceafe2f
--- /dev/null
+++ b/apps/buzz-gpui/scripts/check-remote-provider.test.mjs
@@ -0,0 +1,50 @@
+import assert from "node:assert/strict";
+import { spawnSync } from "node:child_process";
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import test from "node:test";
+import { fileURLToPath } from "node:url";
+
+const check = fileURLToPath(new URL("check-remote-provider.mjs", import.meta.url));
+const valid = {
+  ok: true, name: "relay", version: "0.1.0", description: "Relay provider",
+  protocol_version: 1, config_schema: {}, ops: ["info", "deploy", "stop", "recover"],
+};
+
+function run(info) {
+  const directory = mkdtempSync(join(tmpdir(), "provider-package-check-"));
+  try {
+    const binary = join(directory, "provider");
+    writeFileSync(binary, `#!${process.execPath}\nprocess.stdout.write(${JSON.stringify(JSON.stringify(info))});\n`, { mode: 0o755 });
+    return spawnSync(process.execPath, [check, binary], {
+      encoding: "utf8", timeout: 5_000, maxBuffer: 64 * 1024,
+    });
+  } finally {
+    rmSync(directory, { recursive: true, force: true });
+  }
+}
+
+test("accepts the complete desktop provider response", () => {
+  const result = run(valid);
+  assert.equal(result.status, 0, result.stderr);
+});
+
+test("rejects missing, empty, and wrongly typed desktop metadata", () => {
+  for (const field of ["version", "description", "config_schema"]) {
+    const values = field === "config_schema"
+      ? [undefined, null, [], "schema", 1, false]
+      : [undefined, null, "", 1, false, {}, []];
+    for (const value of values) {
+      const result = run({ ...valid, [field]: value });
+      assert.equal(result.error, undefined);
+      assert.notEqual(result.status, 0, `${field}=${JSON.stringify(value)} must fail`);
+    }
+  }
+});
+
+test("still requires the supported protocol and lifecycle operations", () => {
+  for (const patch of [{ protocol_version: 2 }, { ops: ["info", "deploy"] }, { ops: "deploy stop recover" }]) {
+    assert.notEqual(run({ ...valid, ...patch }).status, 0);
+  }
+});
diff --git a/apps/buzz-gpui/scripts/package-deb.sh b/apps/buzz-gpui/scripts/package-deb.sh
index 5b83489def7..183348e7877 100755
--- a/apps/buzz-gpui/scripts/package-deb.sh
+++ b/apps/buzz-gpui/scripts/package-deb.sh
@@ -13,13 +13,14 @@ set -euo pipefail
 node_version=22.23.3
 node_sha256=df450af89261115ef9f9e3830c3eeb2cc9213b63c720b1af623cb5dcbe2e02de
 here="$(cd "$(dirname "$0")/.." && pwd)"
+repo="$(cd "$here/../.." && pwd)"
 cache="$HOME/.cache/buzz-gpui-deb"
 mkdir -p "$here/dist" "$cache/cargo" "$cache/rustup" "$cache/target"
 # Never leave an older package around to be mistaken for this build.
 rm -f "$here"/dist/*.deb
 
 docker run --rm \
-  -v "$here:$here" \
+  -v "$repo:$repo" \
   -v "$cache/cargo:/root/.cargo" \
   -v "$cache/rustup:/root/.rustup" \
   -v "$cache/target:$here/target-deb" \
@@ -28,6 +29,7 @@ docker run --rm \
   -e NODE_VERSION="$node_version" \
   -e NODE_SHA256="$node_sha256" \
   -e BUZZ_GPUI_RELEASE_VERSION \
+  -e BUZZ_GPUI_VOLTAGE \
   -w "$here" \
   ubuntu:26.04 bash -euo pipefail -c '
     export DEBIAN_FRONTEND=noninteractive
@@ -63,12 +65,22 @@ docker run --rm \
       curl -sSf https://sh.rustup.rs | sh -s -- -y -q --profile minimal --no-modify-path
     fi
     . /root/.cargo/env
-    rustup toolchain list | grep -q stable || rustup default stable
+    # The repository root pins the relay toolchain; GPUI uses its own pin.
+    rustup toolchain install 1.98.1 --profile minimal --no-self-update
+    export RUSTUP_TOOLCHAIN=1.98.1
     command -v cargo-deb >/dev/null || cargo install -q --locked cargo-deb
     # cargo-deb maps the target/release asset paths onto CARGO_TARGET_DIR.
-    cargo build --locked --release -p buzz-gpui
-    cargo deb --no-build -p buzz-gpui -o dist/ \
+    bash scripts/build-package.sh
+    variant=()
+    if [ "${BUZZ_GPUI_VOLTAGE:-0}" = 1 ]; then variant=(--variant voltage); fi
+    cargo deb --no-build -p buzz-gpui "${variant[@]}" -o dist/ \
       ${BUZZ_GPUI_RELEASE_VERSION:+--deb-version "$BUZZ_GPUI_RELEASE_VERSION"}
+    if [ "${BUZZ_GPUI_VOLTAGE:-0}" = 1 ]; then
+      extracted=$(mktemp -d)
+      dpkg-deb -x dist/*.deb "$extracted"
+      "$bundle/node/bin/node" scripts/check-remote-provider.mjs "$extracted/usr/bin/buzz-backend-relay"
+      rm -rf "$extracted"
+    fi
     chown -R "$OWNER" dist
   '
 ls -la "$here"/dist/*.deb
diff --git a/apps/buzz-gpui/scripts/package-macos.sh b/apps/buzz-gpui/scripts/package-macos.sh
index 413e52bb221..353046b14dc 100755
--- a/apps/buzz-gpui/scripts/package-macos.sh
+++ b/apps/buzz-gpui/scripts/package-macos.sh
@@ -32,12 +32,15 @@ export RUSTFLAGS="${RUSTFLAGS:-} -C link-arg=-Wl,-headerpad_max_install_names"
 version="$(cargo metadata --no-deps --format-version 1 \
   | python3 -c 'import json,sys; print(next(p["version"] for p in json.load(sys.stdin)["packages"] if p["name"] == "buzz-gpui"))')"
 arch="$(uname -m)"
-cargo build --locked --release -p buzz-gpui
+bash scripts/build-package.sh
 
 work="$(mktemp -d)"
 app="$work/Buzz.app"
 mkdir -p "$app/Contents/MacOS" "$app/Contents/Resources" dist
 cp target/release/buzz-gpui "$app/Contents/MacOS/"
+if [ "${BUZZ_GPUI_VOLTAGE:-0}" = 1 ]; then
+  cp target/release/buzz-backend-relay "$app/Contents/MacOS/"
+fi
 
 iconset="$work/buzz.iconset"
 mkdir "$iconset"
diff --git a/apps/buzz-gpui/scripts/package-windows.py b/apps/buzz-gpui/scripts/package-windows.py
index e2ee3a2796c..e1a59706f3f 100644
--- a/apps/buzz-gpui/scripts/package-windows.py
+++ b/apps/buzz-gpui/scripts/package-windows.py
@@ -111,7 +111,10 @@ def main():
         if (system / name).exists():
             available[name] = system / name
     pending = []
-    for exe in ("buzz-gpui.exe", "buzzd.exe"):
+    executables = ["buzz-gpui.exe", "buzzd.exe"]
+    if os.environ.get("BUZZ_GPUI_VOLTAGE") == "1":
+        executables.append("buzz-backend-relay.exe")
+    for exe in executables:
         shutil.copy2(repo / "target" / "release" / exe, stage / "bin")
         pending.append(stage / "bin" / exe)
     for name in PLUGINS:
diff --git a/apps/buzz-gpui/scripts/test-package-build.py b/apps/buzz-gpui/scripts/test-package-build.py
new file mode 100644
index 00000000000..588946c5f6c
--- /dev/null
+++ b/apps/buzz-gpui/scripts/test-package-build.py
@@ -0,0 +1,77 @@
+"""Exercise the real package builder with a deterministic Cargo subprocess."""
+import json
+import os
+from pathlib import Path
+import shutil
+import subprocess
+import tempfile
+import unittest
+
+
+class PackageBuild(unittest.TestCase):
+    def run_build(self, voltage, windows=False, fail=False):
+        temporary = tempfile.TemporaryDirectory()
+        self.addCleanup(temporary.cleanup)
+        root = Path(temporary.name)
+        app = root / "apps" / "buzz-gpui"
+        scripts = app / "scripts"
+        scripts.mkdir(parents=True)
+        shutil.copy2(Path(__file__).with_name("build-package.sh"), scripts)
+        binaries = root / "bin"
+        binaries.mkdir()
+        cargo = binaries / "cargo"
+        cargo.write_text('''#!/usr/bin/env python3
+import json, os, pathlib, sys
+args = sys.argv[1:]
+with open(os.environ["CALLS"], "a") as log:
+    log.write(json.dumps(args) + "\\n")
+provider = "buzz-backend-relay" in args
+if provider and os.environ.get("FAIL_PROVIDER") == "1":
+    sys.exit(9)
+target = pathlib.Path(args[args.index("--target-dir")+1] if provider else os.environ["CARGO_TARGET_DIR"])
+release = target / "release"
+release.mkdir(parents=True, exist_ok=True)
+name = "buzz-backend-relay" if provider else "buzz-gpui"
+if os.environ.get("OS") == "Windows_NT":
+    name += ".exe"
+(release / name).write_text("fresh " + name)
+''')
+        cargo.chmod(0o755)
+        env = dict(os.environ, PATH=str(binaries)+os.pathsep+os.environ["PATH"],
+                   CALLS=str(root/"calls.jsonl"), CARGO_TARGET_DIR=str(root/"build"),
+                   BUZZ_GPUI_VOLTAGE="1" if voltage else "0",
+                   OS="Windows_NT" if windows else "Linux", FAIL_PROVIDER="1" if fail else "0")
+        result = subprocess.run(["bash", str(scripts/"build-package.sh")],
+                                env=env, capture_output=True, text=True, timeout=10)
+        calls = [json.loads(line) for line in (root/"calls.jsonl").read_text().splitlines()]
+        return root, result, calls
+
+    def test_voltage_build_enables_remote_ui_and_stages_the_same_builds_provider(self):
+        for windows in [False, True]:
+            with self.subTest(windows=windows):
+                root, result, calls = self.run_build(True, windows)
+                self.assertEqual(result.returncode, 0, result.stderr)
+                self.assertEqual(len(calls), 2)
+                self.assertIn(str(root/"Cargo.toml"), calls[0])
+                self.assertIn("buzz-backend-relay", calls[0])
+                self.assertIn("--features", calls[1])
+                self.assertIn("voltage-sandbox", calls[1])
+                name = "buzz-backend-relay" + (".exe" if windows else "")
+                self.assertEqual((root/"build"/"release"/name).read_text(), "fresh "+name)
+
+    def test_generic_packages_keep_their_existing_feature_set(self):
+        root, result, calls = self.run_build(False)
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(len(calls), 1)
+        self.assertNotIn("--features", calls[0])
+        self.assertFalse((root/"build"/"release"/"buzz-backend-relay").exists())
+
+    def test_provider_failure_stops_packaging_before_building_the_app(self):
+        root, result, calls = self.run_build(True, fail=True)
+        self.assertNotEqual(result.returncode, 0)
+        self.assertEqual(len(calls), 1)
+        self.assertFalse((root/"build"/"release"/"buzz-gpui").exists())
+
+
+if __name__ == "__main__":
+    unittest.main()