fix(install): add rust, cpp, csharp to legacy language alias map (#747)

* fix(install): add rust, cpp, csharp to legacy language alias map

The legacy installer compatibility layer in install-manifests.js was
missing entries for rust, cpp, and csharp — languages that have
rules/ directories and (for rust/cpp) install-components.json entries.

Running `./install.sh rust` fails with "Unknown legacy language: rust"
because LEGACY_LANGUAGE_ALIAS_TO_CANONICAL and
LEGACY_LANGUAGE_EXTRA_MODULE_IDS didn't include these languages.

Fixes the issue reported in #694 by @mpiton.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

* fix(install): complete csharp legacy support and add resolution tests

- Add lang:csharp component to install-components.json with
  framework-language module (matching cpp/rust pattern)
- Update csharp mapping in LEGACY_LANGUAGE_EXTRA_MODULE_IDS from
  empty array to ['framework-language']
- Add end-to-end resolution tests for rust, cpp, and csharp verifying
  framework-language module is included in resolved moduleIds

Addresses review feedback from Copilot, Greptile, CodeRabbit, and Cubic.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Happy <yesreply@happy.engineering>

manifests/install-components.json

@@ -210,6 +210,14 @@
         "framework-language"
       ]
     },
+    {
+      "id": "lang:csharp",
+      "family": "language",
+      "description": "C# coding standards and patterns guidance. Currently resolves through the shared framework-language module.",
+      "modules": [
+        "framework-language"
+      ]
+    },
     {
       "id": "framework:laravel",
       "family": "framework",

scripts/lib/install-manifests.js

@@ -37,6 +37,8 @@ const LEGACY_COMPAT_BASE_MODULE_IDS_BY_TARGET = Object.freeze({
   ],
 });
 const LEGACY_LANGUAGE_ALIAS_TO_CANONICAL = Object.freeze({
+  cpp: 'cpp',
+  csharp: 'csharp',
   go: 'go',
   golang: 'go',
   java: 'java',
@@ -45,15 +47,19 @@ const LEGACY_LANGUAGE_ALIAS_TO_CANONICAL = Object.freeze({
   perl: 'perl',
   php: 'php',
   python: 'python',
+  rust: 'rust',
   swift: 'swift',
   typescript: 'typescript',
 });
 const LEGACY_LANGUAGE_EXTRA_MODULE_IDS = Object.freeze({
+  cpp: ['framework-language'],
+  csharp: ['framework-language'],
   go: ['framework-language'],
   java: ['framework-language'],
   perl: [],
   php: [],
   python: ['framework-language'],
+  rust: ['framework-language'],
   swift: [],
   typescript: ['framework-language'],
 });

tests/lib/install-manifests.test.js

@@ -85,6 +85,9 @@ function runTests() {
     assert.ok(languages.includes('go'));
     assert.ok(languages.includes('golang'));
     assert.ok(languages.includes('kotlin'));
+    assert.ok(languages.includes('rust'));
+    assert.ok(languages.includes('cpp'));
+    assert.ok(languages.includes('csharp'));
   })) passed++; else failed++;
 
   if (test('resolves a real project profile with target-specific skips', () => {
@@ -155,6 +158,39 @@ function runTests() {
     assert.ok(selection.moduleIds.includes('framework-language'));
   })) passed++; else failed++;
 
+  if (test('resolves rust legacy compatibility into framework-language module', () => {
+    const selection = resolveLegacyCompatibilitySelection({
+      target: 'cursor',
+      legacyLanguages: ['rust'],
+    });
+
+    assert.ok(selection.moduleIds.includes('rules-core'));
+    assert.ok(selection.moduleIds.includes('framework-language'),
+      'rust should resolve to framework-language module');
+  })) passed++; else failed++;
+
+  if (test('resolves cpp legacy compatibility into framework-language module', () => {
+    const selection = resolveLegacyCompatibilitySelection({
+      target: 'cursor',
+      legacyLanguages: ['cpp'],
+    });
+
+    assert.ok(selection.moduleIds.includes('rules-core'));
+    assert.ok(selection.moduleIds.includes('framework-language'),
+      'cpp should resolve to framework-language module');
+  })) passed++; else failed++;
+
+  if (test('resolves csharp legacy compatibility into framework-language module', () => {
+    const selection = resolveLegacyCompatibilitySelection({
+      target: 'cursor',
+      legacyLanguages: ['csharp'],
+    });
+
+    assert.ok(selection.moduleIds.includes('rules-core'));
+    assert.ok(selection.moduleIds.includes('framework-language'),
+      'csharp should resolve to framework-language module');
+  })) passed++; else failed++;
+
   if (test('keeps antigravity legacy compatibility selections target-safe', () => {
     const selection = resolveLegacyCompatibilitySelection({
       target: 'antigravity',