diff --git a/apps/desktop/scripts/package.mjs b/apps/desktop/scripts/package.mjs
index 0450ecf4f1..d68dfd5a9f 100644
--- a/apps/desktop/scripts/package.mjs
+++ b/apps/desktop/scripts/package.mjs
@@ -66,6 +66,7 @@ const ARCH_FLAGS = new Map([
 const SUPPORTED_CLI_ARCHS = new Set(["x64", "arm64"]);
 const MAC_ALL_PLATFORM_TARGETS = [
   { platform: "mac", arch: "arm64" },
+  { platform: "mac", arch: "x64" },
   { platform: "win", arch: "x64" },
   { platform: "win", arch: "arm64" },
   { platform: "linux", arch: "x64" },
@@ -338,18 +339,21 @@ export function builderArgsForTarget(
       `-c.directories.output=dist/${target.platform}-${target.arch}`,
     );
   }
-  // electron-builder's update metadata file is `latest.yml` for Windows
-  // regardless of arch (only Linux gets an arch suffix automatically — see
-  // app-builder-lib's getArchPrefixForUpdateFile). Without an explicit
-  // channel override, building Windows x64 and arm64 in two invocations
-  // makes both publish `latest.yml` to the same GitHub Release, so the
-  // second upload overwrites the first and one of the two architectures
-  // ends up with no auto-update metadata. Route Windows arm64 to its own
-  // channel so x64 keeps `latest.yml` and arm64 ships `latest-arm64.yml`;
-  // the renderer-side updater pins the matching channel per arch.
+  // electron-builder only adds an architecture suffix to Linux update
+  // metadata. Windows x64/arm64 would both publish `latest.yml`, while macOS
+  // arm64/x64 would both publish `latest-mac.yml`. Keep the established x64
+  // Windows and arm64 macOS feeds unchanged for installed clients, and route
+  // the additional architectures to explicit channels. updater.ts pins the
+  // matching channel at runtime.
   if (target.platform === "win" && target.arch === "arm64") {
     builderArgs.push("-c.publish.channel=latest-arm64");
   }
+  if (target.platform === "mac" && target.arch === "x64") {
+    // Scope the Electron 39 platform floor to the new Intel package so this
+    // change does not rewrite established Apple Silicon bundle metadata.
+    builderArgs.push("-c.mac.minimumSystemVersion=12.0.0");
+    builderArgs.push("-c.publish.channel=latest-x64");
+  }
   return builderArgs;
 }
 
diff --git a/apps/desktop/scripts/package.test.mjs b/apps/desktop/scripts/package.test.mjs
index cc1c549cb9..3d3f5b5649 100644
--- a/apps/desktop/scripts/package.test.mjs
+++ b/apps/desktop/scripts/package.test.mjs
@@ -241,6 +241,7 @@ describe("resolveBuildMatrix", () => {
       ),
     ).toEqual([
       { platform: "mac", arch: "arm64" },
+      { platform: "mac", arch: "x64" },
       { platform: "win", arch: "x64" },
       { platform: "win", arch: "arm64" },
       { platform: "linux", arch: "x64" },
@@ -322,6 +323,58 @@ describe("builderArgsForTarget", () => {
     ]);
   });
 
+  it("isolates the macOS x64 feed and platform floor", () => {
+    expect(
+      builderArgsForTarget(
+        { platform: "mac", arch: "x64" },
+        {
+          allPlatforms: false,
+          sharedArgs: ["--publish", "always"],
+          platformTargets: { mac: ["dmg", "zip"], win: [], linux: [] },
+          requestedPlatforms: ["mac"],
+          requestedArchs: ["x64"],
+        },
+        "1.2.3",
+        { hostPlatform: "darwin", useScopedOutputDir: true },
+      ),
+    ).toEqual([
+      "-c.extraMetadata.version=1.2.3",
+      "--mac",
+      "dmg",
+      "zip",
+      "--x64",
+      "--publish",
+      "always",
+      "-c.directories.output=dist/mac-x64",
+      "-c.mac.minimumSystemVersion=12.0.0",
+      "-c.publish.channel=latest-x64",
+    ]);
+  });
+
+  it("keeps macOS arm64 on the existing latest-mac update channel", () => {
+    expect(
+      builderArgsForTarget(
+        { platform: "mac", arch: "arm64" },
+        {
+          allPlatforms: false,
+          sharedArgs: ["--publish", "always"],
+          platformTargets: { mac: [], win: [], linux: [] },
+          requestedPlatforms: ["mac"],
+          requestedArchs: ["arm64"],
+        },
+        "1.2.3",
+        { hostPlatform: "darwin", useScopedOutputDir: true },
+      ),
+    ).toEqual([
+      "-c.extraMetadata.version=1.2.3",
+      "--mac",
+      "--arm64",
+      "--publish",
+      "always",
+      "-c.directories.output=dist/mac-arm64",
+    ]);
+  });
+
   it("defaults linux cross-builds to AppImage on non-Linux hosts", () => {
     expect(
       builderArgsForTarget(
diff --git a/apps/desktop/src/main/updater.test.ts b/apps/desktop/src/main/updater.test.ts
index 28221082fe..a778bda248 100644
--- a/apps/desktop/src/main/updater.test.ts
+++ b/apps/desktop/src/main/updater.test.ts
@@ -26,6 +26,7 @@ vi.mock("electron-updater", () => {
     autoDownload: false,
     autoInstallOnAppQuit: false,
     channel: undefined as string | undefined,
+    allowDowngrade: false,
     on: vi.fn((event: string, handler: Handler) => {
       const handlers = ctx.handlers.get(event) ?? [];
       handlers.push(handler);
@@ -50,9 +51,40 @@ vi.mock("electron", () => ({
   },
 }));
 
-import { setupAutoUpdater } from "./updater";
+import {
+  configureMacX64UpdateChannel,
+  setupAutoUpdater,
+} from "./updater";
 import { updaterPreferencesPath } from "./updater-preferences";
 
+describe("macOS x64 update channel", () => {
+  it("does not touch established architecture paths", () => {
+    for (const [platform, arch] of [
+      ["darwin", "arm64"],
+      ["win32", "x64"],
+      ["win32", "arm64"],
+      ["linux", "arm64"],
+    ] as const) {
+      const updater = { channel: null, allowDowngrade: true };
+
+      configureMacX64UpdateChannel(updater, platform, arch);
+
+      expect(updater).toEqual({ channel: null, allowDowngrade: true });
+    }
+  });
+
+  it("does not enable downgrades when selecting an architecture feed", () => {
+    const updater = { channel: null, allowDowngrade: true };
+
+    configureMacX64UpdateChannel(updater, "darwin", "x64");
+
+    expect(updater).toEqual({
+      channel: "latest-x64",
+      allowDowngrade: false,
+    });
+  });
+});
+
 function emitUpdater(event: string, ...args: unknown[]) {
   for (const handler of ctx.handlers.get(event) ?? []) {
     handler(...args);
diff --git a/apps/desktop/src/main/updater.ts b/apps/desktop/src/main/updater.ts
index fa7582dd21..7097fb39be 100644
--- a/apps/desktop/src/main/updater.ts
+++ b/apps/desktop/src/main/updater.ts
@@ -27,6 +27,30 @@ if (process.platform === "win32" && process.arch === "arm64") {
   autoUpdater.channel = "latest-arm64";
 }
 
+interface ChannelConfigurableUpdater {
+  channel: string | null;
+  allowDowngrade: boolean;
+}
+
+export function configureMacX64UpdateChannel(
+  updater: ChannelConfigurableUpdater,
+  platform: NodeJS.Platform = process.platform,
+  arch: string = process.arch,
+): void {
+  if (platform !== "darwin" || arch !== "x64") return;
+
+  // AppUpdater.channel enables allowDowngrade as a side effect. This channel
+  // isolates a CPU architecture, not a release train, so preserve normal
+  // monotonic version behavior after selecting the architecture feed.
+  updater.channel = "latest-x64";
+  updater.allowDowngrade = false;
+}
+
+// electron-builder does not architecture-suffix macOS update metadata.
+// package.mjs publishes macOS x64 as `latest-x64-mac.yml`; the established
+// arm64 feed and runtime path remain unchanged.
+configureMacX64UpdateChannel(autoUpdater);
+
 const STARTUP_CHECK_DELAY_MS = 5_000;
 const PERIODIC_CHECK_INTERVAL_MS = 60 * 60 * 1000; // 1 hour