refactor: align skill install flow with command runner

Author: colinaaa

src/index.ts

@@ -419,27 +419,16 @@ async function runSkillCommand(
   const installationSpinner = spinner();
   installationSpinner.start(`Installing skill ${skill.value}`);
 
-  try {
-    await x('npx', args, {
-      throwOnError: true,
-      nodeOptions: {
-        cwd,
-        stdio: 'pipe',
-      },
-    });
-  } catch (error) {
+  const result = await x('npx', args, {
+    nodeOptions: {
+      cwd,
+      stdio: 'pipe',
+    },
+  });
+
+  if (result.exitCode !== 0) {
     installationSpinner.error(`Failed to install skill ${skill.value}`);
-    const details = [
-      error && typeof error === 'object' && 'output' in error
-        ? (error as { output?: { stderr?: string; stdout?: string } }).output?.stderr
-        : undefined,
-      error && typeof error === 'object' && 'output' in error
-        ? (error as { output?: { stderr?: string; stdout?: string } }).output?.stdout
-        : undefined,
-    ]
-      .filter(Boolean)
-      .join('\n')
-      .trim() || (error instanceof Error ? error.message : String(error));
+    const details = [result.stderr, result.stdout].filter(Boolean).join('\n').trim();
     throw new Error(
       `Failed to install skill "${skill.value}" from "${skill.source}" using command: ${command}${details ? `\n${details}` : ''}`,
     );

test/skills.test.ts

@@ -552,7 +552,11 @@ test('should filter extra skills by template and install using skill override',
 test('should throw with skill context when installation fails', async () => {
   const projectDir = path.join(testDir, 'skills-install-failure');
   createExecCommand(() => {
-    throw new Error('install failed');
+    return {
+      stdout: '',
+      stderr: 'install failed',
+      exitCode: 1,
+    };
   });
 
   const error = await getCreateError(
@@ -602,16 +606,11 @@ test('should trim noisy skills cli output in install errors', async () => {
 ◇  Found 6 skills
 │
 ■  No matching skills found for: non-existent-skill`;
-  createExecCommand(() => {
-    const error = new Error('Process exited with non-zero status (1)') as Error & {
-      output?: { stderr: string; stdout: string };
-    };
-    error.output = {
-      stderr: '',
-      stdout: rawStdout,
-    };
-    throw error;
-  });
+  createExecCommand(() => ({
+    stdout: rawStdout,
+    stderr: '',
+    exitCode: 1,
+  }));
 
   const error = await getCreateError(
     create({
@@ -678,7 +677,7 @@ test('should include spawn errors when skill installation cannot start', async (
     throw new Error('spawn npx ENOENT');
   });
 
-  await expect(
+  const error = await getCreateError(
     create({
       name: 'test',
       root: fixturesDir,
@@ -703,7 +702,10 @@ test('should include spawn errors when skill installation cannot start', async (
         'shared-docs',
       ],
     }),
-  ).rejects.toThrow('spawn npx ENOENT');
+  );
+
+  expect(error).toBeInstanceOf(Error);
+  expect((error as Error).message).toBe('spawn npx ENOENT');
 });
 
 test('should install skills with async spawn so spinner can render during installation', async () => {