diff --git a/packages/installer/test/fuses.test.ts b/packages/installer/test/fuses.test.ts
new file mode 100644
index 0000000..a37a85f
--- /dev/null
+++ b/packages/installer/test/fuses.test.ts
@@ -0,0 +1,136 @@
+import assert from "node:assert/strict";
+import { chmodSync, mkdtempSync, rmSync, statSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import test from "node:test";
+import { FuseV1, readFuses, writeFuse } from "../src/fuses";
+
+const FUSE_SENTINEL = Buffer.from("dL7pKGdnNz796PbbjQWNKmHXBZaB9tsX", "ascii");
+
+test("readFuses decodes the Electron fuse table", () => {
+  withTempDir((root) => {
+    const binary = join(root, "Electron Framework");
+    writeFileSync(
+      binary,
+      fakeElectronBinary({
+        prefix: Buffer.from("prefix"),
+        fuses: ["1", "0", "3", "2", "1"],
+      }),
+    );
+
+    const snapshot = readFuses(binary);
+
+    assert.equal(snapshot.schemaVersion, 1);
+    assert.equal(snapshot.count, 5);
+    assert.deepEqual(snapshot.fuses, ["on", "off", "inherit", "removed", "on"]);
+    assert.equal(snapshot.offset, "prefix".length + FUSE_SENTINEL.length + 2);
+  });
+});
+
+test("writeFuse updates the requested fuse and preserves file mode", () => {
+  withTempDir((root) => {
+    const binary = join(root, "Electron Framework");
+    writeFileSync(
+      binary,
+      fakeElectronBinary({ fuses: ["1", "1", "1", "1", "1"] }),
+    );
+    chmodSync(binary, 0o755);
+    const modeBefore = statSync(binary).mode & 0o777;
+
+    const result = writeFuse(binary, "EnableEmbeddedAsarIntegrityValidation", "off");
+    const snapshot = readFuses(binary);
+
+    assert.deepEqual(result, { from: "on", to: "off" });
+    assert.equal(snapshot.fuses[FuseV1.EnableEmbeddedAsarIntegrityValidation], "off");
+    assert.equal(statSync(binary).mode & 0o777, modeBefore);
+  });
+});
+
+test("writeFuse is a no-op when the fuse already has the requested value", () => {
+  withTempDir((root) => {
+    const binary = join(root, "Electron Framework");
+    writeFileSync(
+      binary,
+      fakeElectronBinary({ fuses: ["1", "1", "1", "1", "0"] }),
+    );
+
+    const result = writeFuse(binary, "EnableEmbeddedAsarIntegrityValidation", "off");
+
+    assert.deepEqual(result, { from: "off", to: "off" });
+    assert.equal(readFuses(binary).fuses[FuseV1.EnableEmbeddedAsarIntegrityValidation], "off");
+  });
+});
+
+test("readFuses rejects binaries without the Electron fuse sentinel", () => {
+  withTempDir((root) => {
+    const binary = join(root, "not-electron");
+    writeFileSync(binary, "plain executable");
+
+    assert.throws(() => readFuses(binary), /Fuse sentinel not found/);
+  });
+});
+
+test("readFuses rejects unsupported fuse schema versions", () => {
+  withTempDir((root) => {
+    const binary = join(root, "Electron Framework");
+    writeFileSync(binary, fakeElectronBinary({ schemaVersion: 2, fuses: ["1"] }));
+
+    assert.throws(() => readFuses(binary), /Unsupported fuse schema version: 2/);
+  });
+});
+
+test("readFuses rejects implausible fuse counts", () => {
+  withTempDir((root) => {
+    const binary = join(root, "Electron Framework");
+    writeFileSync(binary, fakeElectronBinary({ count: 33, fuses: ["1"] }));
+
+    assert.throws(() => readFuses(binary), /Implausible fuse count: 33/);
+  });
+});
+
+test("readFuses rejects unknown fuse byte values", () => {
+  withTempDir((root) => {
+    const binary = join(root, "Electron Framework");
+    writeFileSync(binary, fakeElectronBinary({ rawFuses: Buffer.from([0x78]) }));
+
+    assert.throws(() => readFuses(binary), /Unknown fuse byte 0x78 at index 0/);
+  });
+});
+
+test("writeFuse rejects fuses that are not present in the binary", () => {
+  withTempDir((root) => {
+    const binary = join(root, "Electron Framework");
+    writeFileSync(binary, fakeElectronBinary({ fuses: ["1", "1", "1", "1"] }));
+
+    assert.throws(
+      () => writeFuse(binary, "EnableEmbeddedAsarIntegrityValidation", "off"),
+      /is beyond this binary's fuse count \(4\)/,
+    );
+  });
+});
+
+function fakeElectronBinary(opts: {
+  prefix?: Buffer;
+  schemaVersion?: number;
+  count?: number;
+  fuses?: string[];
+  rawFuses?: Buffer;
+}): Buffer {
+  const rawFuses = opts.rawFuses ?? Buffer.from((opts.fuses ?? []).join(""), "ascii");
+  return Buffer.concat([
+    opts.prefix ?? Buffer.from(""),
+    FUSE_SENTINEL,
+    Buffer.from([opts.schemaVersion ?? 1, opts.count ?? rawFuses.length]),
+    rawFuses,
+    Buffer.from("suffix"),
+  ]);
+}
+
+function withTempDir(fn: (root: string) => void): void {
+  const root = mkdtempSync(join(tmpdir(), "codexpp-fuses-"));
+  try {
+    fn(root);
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+}