fix: preserve file permissions during unpack operation (#43)

- Parse ZIP central directory to extract Unix file permissions
- Restore executable permissions using chmodSync after unpacking files
- Skip permission restoration on Windows (Unix-only feature)
- Add comprehensive test to verify executable and regular file permissions are preserved
- Fix test setup to use npm instead of yarn for consistent build process

Fixes issue where executable files lose their execute permissions after being packed and unpacked, which is critical for extensions containing binary executables or shell scripts.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

test/cli.test.ts

@@ -171,5 +171,83 @@ describe("DXT CLI", () => {
       );
       expect(originalFile2).toEqual(unpackedFile2);
     });
+
+    it("should preserve executable file permissions after packing and unpacking", () => {
+      // Skip this test on Windows since it doesn't support Unix permissions
+      if (process.platform === "win32") {
+        return;
+      }
+
+      const tempExecDir = join(__dirname, "temp-exec-test");
+      const execPackedFilePath = join(__dirname, "test-exec-extension.dxt");
+      const execUnpackedDir = join(__dirname, "temp-exec-unpack-test");
+
+      try {
+        // Create a temporary directory with an executable file
+        fs.mkdirSync(tempExecDir, { recursive: true });
+        fs.writeFileSync(
+          join(tempExecDir, "manifest.json"),
+          JSON.stringify({
+            dxt_version: "1.0",
+            name: "Test Executable Extension",
+            version: "1.0.0",
+            description: "A test extension with executable files",
+            author: {
+              name: "DXT",
+            },
+            server: {
+              type: "node",
+              entry_point: "server/index.js",
+              mcp_config: {
+                command: "node",
+              },
+            },
+          }),
+        );
+        
+        // Create an executable script
+        const executableScript = join(tempExecDir, "run-script.sh");
+        fs.writeFileSync(executableScript, "#!/bin/bash\necho 'Hello from executable'");
+        fs.chmodSync(executableScript, 0o755); // Make it executable
+
+        // Create a regular file for comparison
+        const regularFile = join(tempExecDir, "regular-file.txt");
+        fs.writeFileSync(regularFile, "regular content");
+        fs.chmodSync(regularFile, 0o644); // Regular file permissions
+
+        // Pack the extension
+        execSync(`node ${cliPath} pack ${tempExecDir} ${execPackedFilePath}`, {
+          encoding: "utf-8",
+        });
+
+        // Unpack the extension
+        execSync(`node ${cliPath} unpack ${execPackedFilePath} ${execUnpackedDir}`, {
+          encoding: "utf-8",
+        });
+
+        // Check that the executable file preserved its permissions
+        const originalStats = fs.statSync(executableScript);
+        const unpackedStats = fs.statSync(join(execUnpackedDir, "run-script.sh"));
+        
+        // Check that executable permissions are preserved (0o755)
+        expect(unpackedStats.mode & 0o777).toBe(0o755);
+        expect(originalStats.mode & 0o777).toBe(unpackedStats.mode & 0o777);
+
+        // Check that regular file permissions are preserved (0o644)
+        const originalRegularStats = fs.statSync(regularFile);
+        const unpackedRegularStats = fs.statSync(join(execUnpackedDir, "regular-file.txt"));
+        
+        expect(unpackedRegularStats.mode & 0o777).toBe(0o644);
+        expect(originalRegularStats.mode & 0o777).toBe(unpackedRegularStats.mode & 0o777);
+
+      } finally {
+        // Clean up
+        fs.rmSync(tempExecDir, { recursive: true, force: true });
+        fs.rmSync(execUnpackedDir, { recursive: true, force: true });
+        if (fs.existsSync(execPackedFilePath)) {
+          fs.unlinkSync(execPackedFilePath);
+        }
+      }
+    });
   });
 });