diff --git a/LifeOS/Tools/InstallEngine.ts b/LifeOS/Tools/InstallEngine.ts
index e336412cb1..95768456f6 100644
--- a/LifeOS/Tools/InstallEngine.ts
+++ b/LifeOS/Tools/InstallEngine.ts
@@ -326,7 +326,7 @@ export function scanSettingsHooks(settingsPath: string): SettingsHookScan {
 //  follows the proven logic from the legacy engine actions.ts.
 // ════════════════════════════════════════════════════════════════════
 
-import { cpSync, lstatSync, mkdirSync, readdirSync, readlinkSync, renameSync, symlinkSync, writeFileSync } from "node:fs";
+import { chmodSync, cpSync, lstatSync, mkdirSync, readdirSync, readlinkSync, renameSync, symlinkSync, writeFileSync } from "node:fs";
 import { dirname } from "node:path";
 
 // Extended 2026-07-25 (Forge finding, v7.15.0 re-audit). The set stopped at .ts,
@@ -432,7 +432,9 @@ export function substituteTree(rootDir: string, vars: TemplateVars): { scanned:
     }
     if (after !== before) {
       const tmp = filePath + ".lifeos.tmp";
+      const mode = lstatSync(filePath).mode;
       writeFileSync(tmp, after);
+      chmodSync(tmp, mode);
       renameSync(tmp, filePath);
       modified++;
     }
diff --git a/LifeOS/install/skills/LifeOS/Tools/InstallEngine.ts b/LifeOS/install/skills/LifeOS/Tools/InstallEngine.ts
index e336412cb1..95768456f6 100644
--- a/LifeOS/install/skills/LifeOS/Tools/InstallEngine.ts
+++ b/LifeOS/install/skills/LifeOS/Tools/InstallEngine.ts
@@ -326,7 +326,7 @@ export function scanSettingsHooks(settingsPath: string): SettingsHookScan {
 //  follows the proven logic from the legacy engine actions.ts.
 // ════════════════════════════════════════════════════════════════════
 
-import { cpSync, lstatSync, mkdirSync, readdirSync, readlinkSync, renameSync, symlinkSync, writeFileSync } from "node:fs";
+import { chmodSync, cpSync, lstatSync, mkdirSync, readdirSync, readlinkSync, renameSync, symlinkSync, writeFileSync } from "node:fs";
 import { dirname } from "node:path";
 
 // Extended 2026-07-25 (Forge finding, v7.15.0 re-audit). The set stopped at .ts,
@@ -432,7 +432,9 @@ export function substituteTree(rootDir: string, vars: TemplateVars): { scanned:
     }
     if (after !== before) {
       const tmp = filePath + ".lifeos.tmp";
+      const mode = lstatSync(filePath).mode;
       writeFileSync(tmp, after);
+      chmodSync(tmp, mode);
       renameSync(tmp, filePath);
       modified++;
     }
diff --git a/LifeOS/test/skills/LifeOS/Tools/InstallEngine.test.ts b/LifeOS/test/skills/LifeOS/Tools/InstallEngine.test.ts
new file mode 100644
index 0000000000..c6fbbc9546
--- /dev/null
+++ b/LifeOS/test/skills/LifeOS/Tools/InstallEngine.test.ts
@@ -0,0 +1,27 @@
+import { expect, test } from "bun:test";
+import { chmodSync, mkdtempSync, readFileSync, rmSync, statSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { substituteTree } from "../../../../Tools/InstallEngine";
+
+test("substituteTree preserves executable file modes", () => {
+  if (process.platform === "win32") return;
+
+  const root = mkdtempSync(join(tmpdir(), "lifeos-substitute-"));
+  const hook = join(root, "Example.hook.ts");
+
+  try {
+    writeFileSync(hook, "#!/usr/bin/env bun\nHello, {{PRINCIPAL_NAME}}!\n");
+    chmodSync(hook, 0o755);
+    const modeBefore = statSync(hook).mode & 0o777;
+
+    const result = substituteTree(root, { "{{PRINCIPAL_NAME}}": "Ada" });
+
+    expect(result).toEqual({ scanned: 1, modified: 1, applied: 1 });
+    expect(readFileSync(hook, "utf8")).toContain("Hello, Ada!");
+    expect(statSync(hook).mode & 0o777).toBe(modeBefore);
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});