diff --git a/apps/code/src/main/index.ts b/apps/code/src/main/index.ts
index 57f06f765..29854a8c8 100644
--- a/apps/code/src/main/index.ts
+++ b/apps/code/src/main/index.ts
@@ -1,6 +1,6 @@
 import "reflect-metadata";
 import os from "node:os";
-import { app, BrowserWindow } from "electron";
+import { app, BrowserWindow, dialog } from "electron";
 import log from "electron-log/main";
 import "./utils/logger";
 import "./services/index.js";
@@ -34,6 +34,7 @@ import {
   getLogFilePath,
   readChromiumLogTail,
 } from "./utils/logger";
+import { isMacosPackagedUnsafeBundleLocation } from "./utils/macos-packaged-install-guard";
 import { createWindow } from "./window";
 
 // Single instance lock must be acquired FIRST before any other app setup
@@ -180,6 +181,31 @@ registerDeepLinkHandlers();
 initializePostHog();
 
 app.whenReady().then(async () => {
+  if (
+    process.platform === "darwin" &&
+    app.isPackaged &&
+    isMacosPackagedUnsafeBundleLocation(app.getAppPath(), process.execPath)
+  ) {
+    const appPath = app.getAppPath();
+    const exePath = process.execPath;
+    const bundleRoot = exePath.replace(/\/Contents\/MacOS\/[^/]+$/, "");
+    log.warn(
+      "Refusing to start: packaged app is on App Translocation or a read-only non-root volume",
+      { appPath, exePath },
+    );
+    dialog.showMessageBoxSync({
+      type: "warning",
+      title: "Move PostHog Code to Applications",
+      message: `PostHog Code is running from a location with read-only access:\n\n${bundleRoot}`,
+      detail:
+        "After quitting, move PostHog Code to your Applications folder, then open it from there.",
+      buttons: ["Quit"],
+      defaultId: 0,
+    });
+    app.quit();
+    return;
+  }
+
   const commit = __BUILD_COMMIT__ ?? "dev";
   const buildDate = __BUILD_DATE__ ?? "dev";
   log.info(
diff --git a/apps/code/src/main/utils/macos-packaged-install-guard.test.ts b/apps/code/src/main/utils/macos-packaged-install-guard.test.ts
new file mode 100644
index 000000000..49af40d9f
--- /dev/null
+++ b/apps/code/src/main/utils/macos-packaged-install-guard.test.ts
@@ -0,0 +1,202 @@
+import { describe, expect, it, vi } from "vitest";
+import {
+  type DarwinMountEntry,
+  isMacosAppTranslocationPath,
+  isMacosPackagedUnsafeBundleLocation,
+  isMacosPathOnReadOnlyNonRootMountFromTable,
+  parseDarwinMountTable,
+  type ReadDarwinMountTable,
+} from "./macos-packaged-install-guard";
+
+describe("isMacosAppTranslocationPath", () => {
+  it.each([
+    {
+      case: "appPath is translocated",
+      appPath:
+        "/private/var/folders/yf/xx/AppTranslocation/C6283C3C-9D6E-4D81-A7D5-8BA2567ED486/d/PostHog Code.app/Contents/Resources/app.asar",
+      exePath: "/Applications/PostHog Code.app/Contents/MacOS/PostHog Code",
+      expected: true,
+    },
+    {
+      case: "exePath is translocated",
+      appPath: "/Applications/PostHog Code.app/Contents/Resources/app.asar",
+      exePath:
+        "/private/var/folders/yf/xx/AppTranslocation/C6283C3C/d/PostHog Code.app/Contents/MacOS/PostHog Code",
+      expected: true,
+    },
+    {
+      case: "neither path is translocated (/Applications)",
+      appPath: "/Applications/PostHog Code.app/Contents/Resources/app.asar",
+      exePath: "/Applications/PostHog Code.app/Contents/MacOS/PostHog Code",
+      expected: false,
+    },
+    {
+      case: "neither path is translocated (/Users)",
+      appPath: "/Users/dev/PostHog Code.app/Contents/Resources/app.asar",
+      exePath: "/Users/dev/PostHog Code.app/Contents/MacOS/PostHog Code",
+      expected: false,
+    },
+  ])("$case → $expected", ({ appPath, exePath, expected }) => {
+    expect(isMacosAppTranslocationPath(appPath, exePath)).toBe(expected);
+  });
+});
+
+describe("parseDarwinMountTable", () => {
+  it.each<{
+    case: string;
+    input: string;
+    expected: DarwinMountEntry[];
+  }>([
+    {
+      case: "standard macOS mount lines",
+      input: `/dev/disk3s1s1 on / (apfs, sealed, local, read-only, journaled)
+/dev/disk7s1 on /Volumes/My Dmg (apfs, local, read-only, journaled)
+/dev/disk5s1 on /Volumes/Writable (apfs, local, journaled)
+`,
+      expected: [
+        {
+          mountPoint: "/",
+          options: "apfs, sealed, local, read-only, journaled",
+        },
+        {
+          mountPoint: "/Volumes/My Dmg",
+          options: "apfs, local, read-only, journaled",
+        },
+        { mountPoint: "/Volumes/Writable", options: "apfs, local, journaled" },
+      ],
+    },
+    {
+      case: "mount point name contains ' (' — anchors to trailing options",
+      input:
+        "/dev/disk9s1 on /Volumes/My Backup (2) (apfs, local, read-only, journaled)\n",
+      expected: [
+        {
+          mountPoint: "/Volumes/My Backup (2)",
+          options: "apfs, local, read-only, journaled",
+        },
+      ],
+    },
+  ])("parses: $case", ({ input, expected }) => {
+    expect(parseDarwinMountTable(input)).toEqual(expected);
+  });
+});
+
+describe("isMacosPathOnReadOnlyNonRootMountFromTable", () => {
+  const baseTable = `/dev/disk3s1s1 on / (apfs, sealed, local, read-only, journaled)
+/dev/disk7s1 on /Volumes/ReadOnlyVol (apfs, local, read-only, journaled)
+/dev/disk5s1 on /Volumes/Writable (apfs, local, journaled)
+`;
+  const nestedTable = `/dev/x on / (apfs, read-only)
+/dev/y on /Volumes/RW (apfs, local, journaled)
+/dev/z on /Volumes/RW/nested (apfs, local, read-only)
+`;
+
+  it.each([
+    {
+      case: "path under read-only / is ignored (Users)",
+      table: baseTable,
+      path: "/Users/me/app",
+      expected: false,
+    },
+    {
+      case: "path under read-only / is ignored (Applications)",
+      table: baseTable,
+      path: "/Applications/Foo.app",
+      expected: false,
+    },
+    {
+      case: "read-only non-root volume",
+      table: baseTable,
+      path: "/Volumes/ReadOnlyVol/PostHog Code.app/Contents/MacOS/PostHog Code",
+      expected: true,
+    },
+    {
+      case: "writable non-root volume",
+      table: baseTable,
+      path: "/Volumes/Writable/out/PostHog Code.app/Contents/MacOS/PostHog Code",
+      expected: false,
+    },
+    {
+      case: "nested read-only mount wins over writable parent",
+      table: nestedTable,
+      path: "/Volumes/RW/nested/app",
+      expected: true,
+    },
+    {
+      case: "writable parent wins when no deeper match",
+      table: nestedTable,
+      path: "/Volumes/RW/other/app",
+      expected: false,
+    },
+  ])("$case → $expected", ({ table, path, expected }) => {
+    expect(isMacosPathOnReadOnlyNonRootMountFromTable(path, table)).toBe(
+      expected,
+    );
+  });
+});
+
+describe("isMacosPackagedUnsafeBundleLocation", () => {
+  const writableMountTable = `/dev/disk3s1s1 on / (apfs, sealed, local, read-only, journaled)
+/dev/disk5s1 on /Volumes/build (apfs, local, journaled)
+/dev/disk6s1 on /Applications (apfs, local, journaled)
+`;
+  const readOnlyMountTable = `/dev/disk3s1s1 on / (apfs, sealed, local, read-only, journaled)
+/dev/disk7s1 on /Volumes/ReadOnlyVol (apfs, local, read-only, journaled)
+`;
+
+  it.each<{
+    case: string;
+    appPath: string;
+    exePath: string;
+    readMountTable: ReadDarwinMountTable;
+    expected: boolean;
+  }>([
+    {
+      case: "translocated bundle",
+      appPath:
+        "/private/var/.../AppTranslocation/UUID/d/PostHog Code.app/Contents/Resources/app.asar",
+      exePath: "/Applications/PostHog Code.app/Contents/MacOS/PostHog Code",
+      readMountTable: () => writableMountTable,
+      expected: true,
+    },
+    {
+      case: "ordinary non-translocated path on a writable mount",
+      appPath:
+        "/Volumes/build/out/PostHog Code.app/Contents/Resources/app.asar",
+      exePath:
+        "/Volumes/build/out/PostHog Code.app/Contents/MacOS/PostHog Code",
+      readMountTable: () => writableMountTable,
+      expected: false,
+    },
+    {
+      case: "bundle on a read-only non-root volume",
+      appPath:
+        "/Volumes/ReadOnlyVol/PostHog Code.app/Contents/Resources/app.asar",
+      exePath:
+        "/Volumes/ReadOnlyVol/PostHog Code.app/Contents/MacOS/PostHog Code",
+      readMountTable: () => readOnlyMountTable,
+      expected: true,
+    },
+    {
+      case: "mount table cannot be read (degrade to non-blocking)",
+      appPath: "/Applications/PostHog Code.app/Contents/Resources/app.asar",
+      exePath: "/Applications/PostHog Code.app/Contents/MacOS/PostHog Code",
+      readMountTable: () => null,
+      expected: false,
+    },
+  ])("$case → $expected", ({ appPath, exePath, readMountTable, expected }) => {
+    expect(
+      isMacosPackagedUnsafeBundleLocation(appPath, exePath, readMountTable),
+    ).toBe(expected);
+  });
+
+  it("short-circuits on translocation without reading the mount table", () => {
+    const readMountTable = vi.fn(() => writableMountTable);
+    isMacosPackagedUnsafeBundleLocation(
+      "/private/var/.../AppTranslocation/UUID/d/PostHog Code.app/Contents/Resources/app.asar",
+      "/Applications/PostHog Code.app/Contents/MacOS/PostHog Code",
+      readMountTable,
+    );
+    expect(readMountTable).not.toHaveBeenCalled();
+  });
+});
diff --git a/apps/code/src/main/utils/macos-packaged-install-guard.ts b/apps/code/src/main/utils/macos-packaged-install-guard.ts
new file mode 100644
index 000000000..a0a11578c
--- /dev/null
+++ b/apps/code/src/main/utils/macos-packaged-install-guard.ts
@@ -0,0 +1,138 @@
+import { execFileSync } from "node:child_process";
+import path from "node:path";
+
+const APP_TRANSLOCATION_SEGMENT = "AppTranslocation";
+const MOUNT_READ_TIMEOUT_MS = 3000;
+
+export type DarwinMountEntry = {
+  mountPoint: string;
+  options: string;
+};
+
+/**
+ * Reads the Darwin mount table. Returns `null` when the table cannot be
+ * obtained (e.g. `/sbin/mount` is missing, times out, or exits non-zero).
+ */
+export type ReadDarwinMountTable = () => string | null;
+
+/** Parse `/sbin/mount` lines: `<device> on <mountPoint> (<opts>)` */
+export function parseDarwinMountTable(output: string): DarwinMountEntry[] {
+  const entries: DarwinMountEntry[] = [];
+  for (const line of output.split("\n")) {
+    const onMarker = line.indexOf(" on ");
+    if (onMarker === -1) continue;
+    const afterOn = line.slice(onMarker + 4);
+    // `lastIndexOf` anchors to the trailing options block, so mount points
+    // whose display names contain " (" (e.g. "/Volumes/My Backup (2)") still
+    // parse correctly. The `line.endsWith(")")` check guarantees those parens
+    // really are the options.
+    const openParen = afterOn.lastIndexOf(" (");
+    if (openParen === -1 || !line.endsWith(")")) continue;
+    const mountPoint = afterOn.slice(0, openParen);
+    const options = afterOn.slice(openParen + 2, -1);
+    entries.push({ mountPoint, options });
+  }
+  return entries;
+}
+
+function mountOptionsImplyReadOnly(options: string): boolean {
+  return options.toLowerCase().includes("read-only");
+}
+
+function longestMatchingMount(
+  resolvedPath: string,
+  entries: DarwinMountEntry[],
+): DarwinMountEntry | null {
+  let best: DarwinMountEntry | null = null;
+  for (const e of entries) {
+    const mp = e.mountPoint;
+    // For `/` we'd otherwise build `//` which no real path starts with, so the
+    // root mount would silently drop out of the comparison and the
+    // `best.mountPoint === "/"` guard below would be unreachable.
+    const under =
+      resolvedPath === mp ||
+      resolvedPath.startsWith(mp === "/" ? "/" : `${mp}/`);
+    if (!under) continue;
+    if (!best || mp.length > best.mountPoint.length) {
+      best = e;
+    }
+  }
+  return best;
+}
+
+/**
+ * True when `resolvedAbsolutePath` sits on a **non-root** mount that `mount(8)`
+ * reports as read-only (e.g. many DMGs, some external volumes).
+ *
+ * Ignores read-only `/` — on sealed macOS the system volume is read-only while
+ * normal apps under /Applications or /Users still work.
+ */
+export function isMacosPathOnReadOnlyNonRootMountFromTable(
+  resolvedAbsolutePath: string,
+  mountTable: string,
+): boolean {
+  const normalized = path.resolve(resolvedAbsolutePath);
+  const entries = parseDarwinMountTable(mountTable);
+  const best = longestMatchingMount(normalized, entries);
+  if (!best || best.mountPoint === "/") {
+    return false;
+  }
+  return mountOptionsImplyReadOnly(best.options);
+}
+
+/**
+ * Reads `/sbin/mount` synchronously. A short timeout keeps a hung NFS/SMB
+ * share from freezing app startup — the exact failure mode this guard exists
+ * to prevent. Returns `null` on any failure so callers can degrade to "don't
+ * block".
+ */
+function readDarwinMountTableSync(): string | null {
+  try {
+    return execFileSync("/sbin/mount", {
+      encoding: "utf8",
+      maxBuffer: 10 * 1024 * 1024,
+      timeout: MOUNT_READ_TIMEOUT_MS,
+    });
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * True when either path is under macOS App Translocation (read-only runtime).
+ * Caller should gate on packaged darwin before using this to block startup.
+ */
+export function isMacosAppTranslocationPath(
+  appPath: string,
+  exePath: string,
+): boolean {
+  return (
+    appPath.includes(APP_TRANSLOCATION_SEGMENT) ||
+    exePath.includes(APP_TRANSLOCATION_SEGMENT)
+  );
+}
+
+/**
+ * Packaged macOS: translocated bundle path, or binary on a non-root read-only
+ * mount (see mount(8)).
+ *
+ * `readMountTable` is injectable so tests can drive the mount-table branch
+ * deterministically instead of relying on the host's real `/sbin/mount`.
+ */
+export function isMacosPackagedUnsafeBundleLocation(
+  appPath: string,
+  exePath: string,
+  readMountTable: ReadDarwinMountTable = readDarwinMountTableSync,
+): boolean {
+  if (isMacosAppTranslocationPath(appPath, exePath)) {
+    return true;
+  }
+  const table = readMountTable();
+  if (table === null) {
+    return false;
+  }
+  return isMacosPathOnReadOnlyNonRootMountFromTable(
+    path.resolve(exePath),
+    table,
+  );
+}