feat: multi-runtime selection in interactive installer (#1281)

The interactive prompt now accepts comma-separated or space-separated
choices (e.g., "1,4,6" or "1 4 6") to install multiple runtimes in
one go, without needing --all or running the installer multiple times.

- Replaced if/else-if chain with runtimeMap lookup + split parser
- Added hint text: "Select multiple: 1,4,6 or 1 4 6"
- Invalid choices silently filtered, duplicates deduplicated
- Empty input still defaults to Claude Code
- Choice "8" still selects all runtimes

Tests: 10 new tests covering comma/space/mixed separators,
deduplication, invalid input filtering, order preservation,
and source-level assertions.

Closes #1281

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/multi-runtime-select.test.cjs

@@ -0,0 +1,145 @@
+/**
+ * Tests for multi-runtime selection in the interactive installer prompt.
+ * Verifies that promptRuntime accepts comma-separated, space-separated,
+ * and single-choice inputs, deduplicates, and falls back to claude.
+ * See issue #1281.
+ */
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+
+// Read install.js source to extract the runtimeMap and parsing logic
+const installSrc = fs.readFileSync(
+  path.join(__dirname, '..', 'bin', 'install.js'),
+  'utf8'
+);
+
+// Extract runtimeMap from source for validation
+const runtimeMap = {
+  '1': 'claude',
+  '2': 'opencode',
+  '3': 'gemini',
+  '4': 'codex',
+  '5': 'copilot',
+  '6': 'antigravity',
+  '7': 'cursor'
+};
+const allRuntimes = ['claude', 'opencode', 'gemini', 'codex', 'copilot', 'antigravity', 'cursor'];
+
+/**
+ * Simulate the parsing logic from promptRuntime without requiring readline.
+ * This mirrors the exact logic in the rl.question callback.
+ */
+function parseRuntimeInput(input) {
+  input = input.trim() || '1';
+
+  if (input === '8') {
+    return allRuntimes;
+  }
+
+  const choices = input.split(/[\s,]+/).filter(Boolean);
+  const selected = [];
+  for (const c of choices) {
+    const runtime = runtimeMap[c];
+    if (runtime && !selected.includes(runtime)) {
+      selected.push(runtime);
+    }
+  }
+
+  return selected.length > 0 ? selected : ['claude'];
+}
+
+describe('multi-runtime selection parsing', () => {
+  test('single choice returns single runtime', () => {
+    assert.deepStrictEqual(parseRuntimeInput('1'), ['claude']);
+    assert.deepStrictEqual(parseRuntimeInput('4'), ['codex']);
+    assert.deepStrictEqual(parseRuntimeInput('7'), ['cursor']);
+  });
+
+  test('comma-separated choices return multiple runtimes', () => {
+    assert.deepStrictEqual(parseRuntimeInput('1,4,6'), ['claude', 'codex', 'antigravity']);
+    assert.deepStrictEqual(parseRuntimeInput('2,3'), ['opencode', 'gemini']);
+  });
+
+  test('space-separated choices return multiple runtimes', () => {
+    assert.deepStrictEqual(parseRuntimeInput('1 4 6'), ['claude', 'codex', 'antigravity']);
+    assert.deepStrictEqual(parseRuntimeInput('5 7'), ['copilot', 'cursor']);
+  });
+
+  test('mixed comma and space separators work', () => {
+    assert.deepStrictEqual(parseRuntimeInput('1, 4, 6'), ['claude', 'codex', 'antigravity']);
+    assert.deepStrictEqual(parseRuntimeInput('2 , 5'), ['opencode', 'copilot']);
+  });
+
+  test('choice 8 returns all runtimes', () => {
+    assert.deepStrictEqual(parseRuntimeInput('8'), allRuntimes);
+  });
+
+  test('empty input defaults to claude', () => {
+    assert.deepStrictEqual(parseRuntimeInput(''), ['claude']);
+    assert.deepStrictEqual(parseRuntimeInput('   '), ['claude']);
+  });
+
+  test('invalid choices are ignored, falls back to claude if all invalid', () => {
+    assert.deepStrictEqual(parseRuntimeInput('9'), ['claude']);
+    assert.deepStrictEqual(parseRuntimeInput('0'), ['claude']);
+    assert.deepStrictEqual(parseRuntimeInput('abc'), ['claude']);
+  });
+
+  test('invalid choices mixed with valid are filtered out', () => {
+    assert.deepStrictEqual(parseRuntimeInput('1,9,4'), ['claude', 'codex']);
+    assert.deepStrictEqual(parseRuntimeInput('abc 3 xyz'), ['gemini']);
+  });
+
+  test('duplicate choices are deduplicated', () => {
+    assert.deepStrictEqual(parseRuntimeInput('1,1,1'), ['claude']);
+    assert.deepStrictEqual(parseRuntimeInput('4,4,6,6'), ['codex', 'antigravity']);
+  });
+
+  test('preserves selection order', () => {
+    assert.deepStrictEqual(parseRuntimeInput('6,1,4'), ['antigravity', 'claude', 'codex']);
+    assert.deepStrictEqual(parseRuntimeInput('7,2,5'), ['cursor', 'opencode', 'copilot']);
+  });
+});
+
+describe('install.js source contains multi-select support', () => {
+  test('runtimeMap is defined with all 7 runtimes', () => {
+    for (const [key, name] of Object.entries(runtimeMap)) {
+      assert.ok(
+        installSrc.includes(`'${key}': '${name}'`),
+        `runtimeMap has ${key} -> ${name}`
+      );
+    }
+  });
+
+  test('allRuntimes array contains all runtimes', () => {
+    const match = installSrc.match(/const allRuntimes = \[([^\]]+)\]/);
+    assert.ok(match, 'allRuntimes array found');
+    for (const rt of allRuntimes) {
+      assert.ok(match[1].includes(`'${rt}'`), `allRuntimes includes ${rt}`);
+    }
+  });
+
+  test('prompt text shows multi-select hint', () => {
+    assert.ok(
+      installSrc.includes('Select multiple'),
+      'prompt includes multi-select instructions'
+    );
+  });
+
+  test('parsing uses split with comma and space regex', () => {
+    assert.ok(
+      installSrc.includes("split(/[\\s,]+/)"),
+      'input is split on commas and whitespace'
+    );
+  });
+
+  test('deduplication check exists', () => {
+    assert.ok(
+      installSrc.includes('!selected.includes(runtime)'),
+      'deduplication guard exists'
+    );
+  });
+});