diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 32093062..a6da7661 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -151,8 +151,10 @@ jobs:
       - name: Build unsigned macOS packages
         run: pnpm package:mac:unsigned
 
-      - name: Inspect macOS zip
-        run: pnpm inspect:package -- release/*.zip
+      - name: Inspect macOS packages
+        run: |
+          pnpm inspect:package -- release/*.zip
+          pnpm inspect:dmg -- release/*.dmg
 
       - name: Stage macOS artifacts
         shell: bash
diff --git a/package.json b/package.json
index 76649a56..58bf2d48 100644
--- a/package.json
+++ b/package.json
@@ -19,7 +19,8 @@
     "package:mac:unsigned": "node scripts/package-mac-unsigned.mjs",
     "package:dir": "pnpm prepackage && node scripts/run-electron-builder.mjs --linux --x64 --dir",
     "inspect:package": "node scripts/inspect-package.mjs",
-    "test:packaging": "node --test scripts/packaging.test.mjs",
+    "inspect:dmg": "node scripts/inspect-macos-dmg.mjs",
+    "test:packaging": "node --test scripts/packaging.test.mjs scripts/inspect-macos-dmg.test.mjs",
     "test:tooling": "node --test scripts/check-structure.test.mjs scripts/check-provenance.test.mjs scripts/deploy-site.test.mjs scripts/tailnet-gateway.test.mjs scripts/tailnet-service.test.mjs",
     "check:structure": "node scripts/check-structure.mjs",
     "check:provenance": "node scripts/check-provenance.mjs",
diff --git a/scripts/inspect-macos-dmg.mjs b/scripts/inspect-macos-dmg.mjs
new file mode 100644
index 00000000..c2f6b820
--- /dev/null
+++ b/scripts/inspect-macos-dmg.mjs
@@ -0,0 +1,143 @@
+import { mkdtempSync, readdirSync, rmdirSync, statSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { extname, join, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { spawnSync } from "node:child_process";
+
+import { inspectPackage, locateAppRoot } from "./inspect-package.mjs";
+
+function asError(error) {
+  return error instanceof Error ? error : new Error(String(error));
+}
+
+function appendCleanupError(primary, cleanup, message) {
+  const cleanupError = asError(cleanup);
+  if (primary === null) return cleanupError;
+  return new AggregateError([primary, cleanupError], message);
+}
+
+function defaultRunCommand(command, args) {
+  const result = spawnSync(command, args, { stdio: "inherit" });
+  if (result.error) throw result.error;
+  if (result.status !== 0) {
+    throw new Error(`${command} exited with status ${result.status ?? "unknown"}`);
+  }
+}
+
+function defaultIsFile(path) {
+  try {
+    return statSync(path).isFile();
+  } catch {
+    return false;
+  }
+}
+
+function defaultReadMountedEntries(path) {
+  return readdirSync(path, { withFileTypes: true });
+}
+
+export function findMountedApp(mountPoint, readMountedEntries = defaultReadMountedEntries) {
+  const apps = readMountedEntries(mountPoint)
+    .filter((entry) => entry.isDirectory() && extname(entry.name).toLowerCase() === ".app")
+    .map((entry) => join(mountPoint, entry.name));
+  if (apps.length !== 1) {
+    throw new Error(`expected exactly one macOS app in mounted DMG; found ${apps.length}`);
+  }
+  return apps[0];
+}
+
+export function inspectMacosDmg(dmgPath, dependencies = {}) {
+  const platform = dependencies.platform ?? process.platform;
+  if (platform !== "darwin") {
+    throw new Error(`DMG inspection requires macOS (darwin); current platform is ${platform}`);
+  }
+
+  const absoluteDmg = resolve(dmgPath);
+  const isFile = dependencies.isFile ?? defaultIsFile;
+  if (extname(absoluteDmg).toLowerCase() !== ".dmg" || !isFile(absoluteDmg)) {
+    throw new Error(`DMG does not exist or is not a file: ${absoluteDmg}`);
+  }
+
+  const createMountPoint =
+    dependencies.createMountPoint ?? (() => mkdtempSync(join(tmpdir(), "t4-code-dmg-")));
+  const removeMountPoint = dependencies.removeMountPoint ?? rmdirSync;
+  const readMountedEntries = dependencies.readMountedEntries ?? defaultReadMountedEntries;
+  const inspectArtifact = dependencies.inspectArtifact ?? inspectPackage;
+  const resolveAppRoot = dependencies.resolveAppRoot ?? locateAppRoot;
+  const runCommand = dependencies.runCommand ?? defaultRunCommand;
+  const mountPoint = createMountPoint();
+
+  let failure = null;
+  let mounted = false;
+  let detached = false;
+  let inspection;
+  try {
+    runCommand("hdiutil", [
+      "attach",
+      "-readonly",
+      "-nobrowse",
+      "-noautoopen",
+      "-mountpoint",
+      mountPoint,
+      absoluteDmg,
+    ]);
+    mounted = true;
+    const appPath = findMountedApp(mountPoint, readMountedEntries);
+    inspection = inspectArtifact(resolveAppRoot(appPath));
+  } catch (error) {
+    failure = asError(error);
+  } finally {
+    if (mounted) {
+      try {
+        runCommand("hdiutil", ["detach", mountPoint]);
+        detached = true;
+      } catch (normalDetachError) {
+        try {
+          runCommand("hdiutil", ["detach", "-force", mountPoint]);
+          detached = true;
+        } catch (forceDetachError) {
+          failure = appendCleanupError(
+            failure,
+            new AggregateError(
+              [asError(normalDetachError), asError(forceDetachError)],
+              `could not detach mounted DMG at ${mountPoint}`,
+            ),
+            "DMG inspection failed and cleanup could not detach the image",
+          );
+        }
+      }
+    }
+
+    if (!mounted || detached) {
+      try {
+        removeMountPoint(mountPoint);
+      } catch (error) {
+        failure = appendCleanupError(
+          failure,
+          error,
+          "DMG inspection failed and cleanup could not remove its mount point",
+        );
+      }
+    }
+  }
+
+  if (failure !== null) throw failure;
+  return inspection;
+}
+
+const isMain = process.argv[1] && resolve(process.argv[1]) === resolve(fileURLToPath(import.meta.url));
+if (isMain) {
+  const paths = process.argv.slice(2).filter((argument) => argument !== "--");
+  if (paths.length !== 1) {
+    console.error("usage: pnpm inspect:dmg -- <artifact.dmg>");
+    process.exitCode = 1;
+  } else {
+    try {
+      const result = inspectMacosDmg(paths[0]);
+      console.log(`${paths[0]}: mounted read-only and inspected ${result.asarEntries} ASAR entries`);
+    } catch (error) {
+      console.error(error instanceof Error ? error.message : String(error));
+      process.exitCode = 1;
+    }
+  }
+}
diff --git a/scripts/inspect-macos-dmg.test.mjs b/scripts/inspect-macos-dmg.test.mjs
new file mode 100644
index 00000000..9fd08bb1
--- /dev/null
+++ b/scripts/inspect-macos-dmg.test.mjs
@@ -0,0 +1,112 @@
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { test } from "node:test";
+import { resolve } from "node:path";
+
+import { findMountedApp, inspectMacosDmg } from "./inspect-macos-dmg.mjs";
+
+const dmgPath = "/tmp/T4-Code-0.1.3-mac-arm64.dmg";
+const mountPoint = "/tmp/t4-code-dmg-test";
+
+function directory(name) {
+  return { name, isDirectory: () => true };
+}
+
+function fixture(overrides = {}) {
+  const calls = [];
+  const dependencies = {
+    platform: "darwin",
+    isFile: () => true,
+    createMountPoint: () => mountPoint,
+    readMountedEntries: () => [directory("T4 Code.app")],
+    resolveAppRoot: (path) => `${path}/Contents`,
+    inspectArtifact: (path) => {
+      calls.push(["inspect", path]);
+      return { asarEntries: 42 };
+    },
+    runCommand: (command, args) => calls.push([command, ...args]),
+    removeMountPoint: (path) => calls.push(["remove", path]),
+    ...overrides,
+  };
+  return { calls, dependencies };
+}
+
+test("DMG inspection mounts read-only, inspects the app, detaches, then removes the mount point", () => {
+  const { calls, dependencies } = fixture();
+  assert.deepEqual(inspectMacosDmg(dmgPath, dependencies), { asarEntries: 42 });
+  assert.deepEqual(calls, [
+    [
+      "hdiutil",
+      "attach",
+      "-readonly",
+      "-nobrowse",
+      "-noautoopen",
+      "-mountpoint",
+      mountPoint,
+      dmgPath,
+    ],
+    ["inspect", `${mountPoint}/T4 Code.app/Contents`],
+    ["hdiutil", "detach", mountPoint],
+    ["remove", mountPoint],
+  ]);
+});
+
+test("DMG inspection detaches even when package inspection fails", () => {
+  const { calls, dependencies } = fixture({
+    inspectArtifact: (path) => {
+      calls.push(["inspect", path]);
+      throw new Error("bad package");
+    },
+  });
+  assert.throws(() => inspectMacosDmg(dmgPath, dependencies), /bad package/);
+  assert.deepEqual(calls.slice(-2), [
+    ["hdiutil", "detach", mountPoint],
+    ["remove", mountPoint],
+  ]);
+});
+
+test("DMG inspection force-detaches when the normal detach is busy", () => {
+  const { calls, dependencies } = fixture({
+    runCommand: (command, args) => {
+      calls.push([command, ...args]);
+      if (args[0] === "detach" && args[1] !== "-force") throw new Error("busy");
+    },
+  });
+  assert.deepEqual(inspectMacosDmg(dmgPath, dependencies), { asarEntries: 42 });
+  assert.deepEqual(calls.slice(-3), [
+    ["hdiutil", "detach", mountPoint],
+    ["hdiutil", "detach", "-force", mountPoint],
+    ["remove", mountPoint],
+  ]);
+});
+
+test("DMG inspection fails closed and preserves the mount point when detach cannot complete", () => {
+  const { calls, dependencies } = fixture({
+    runCommand: (command, args) => {
+      calls.push([command, ...args]);
+      if (args[0] === "detach") throw new Error("still busy");
+    },
+  });
+  assert.throws(() => inspectMacosDmg(dmgPath, dependencies), /could not detach mounted DMG/);
+  assert.equal(calls.some(([command]) => command === "remove"), false);
+});
+
+test("mounted DMGs must contain exactly one application bundle", () => {
+  assert.equal(
+    findMountedApp(mountPoint, () => [directory("T4 Code.app")]),
+    `${mountPoint}/T4 Code.app`,
+  );
+  assert.throws(() => findMountedApp(mountPoint, () => []), /found 0/);
+  assert.throws(
+    () => findMountedApp(mountPoint, () => [directory("One.app"), directory("Two.app")]),
+    /found 2/,
+  );
+});
+
+test("release workflow inspects the DMG before staging it for publication", () => {
+  const workflow = readFileSync(resolve(import.meta.dirname, "../.github/workflows/release.yml"), "utf8");
+  const inspect = workflow.indexOf("pnpm inspect:dmg -- release/*.dmg");
+  const stage = workflow.indexOf("cp release/T4-Code-*.dmg");
+  assert.ok(inspect >= 0, "release workflow must invoke the DMG inspector");
+  assert.ok(stage > inspect, "DMG inspection must run before staging the artifact");
+});