Resolve virtual provides and surface engine failures in package check

dnf repoquery only matches exact package names, so virtual provides
like "vim" (satisfied by vim-enhanced etc.) falsely failed the Check
step even though rpm-ostree install would resolve them fine. It also
silently reported a broken dnf (e.g. a plugin enabled in config but
missing on disk) as "package not found" instead of flagging it as its
own distinct failure.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/ostree_service.dart

@@ -1,6 +1,18 @@
 import 'dart:convert';
 import 'dart:io';
 
+/// Thrown when `dnf` itself fails to run (e.g. a plugin that's enabled in
+/// config but missing on disk) rather than genuinely finding no match.
+/// Distinct from "package not found" so the UI can tell a broken search
+/// engine apart from a bad package name.
+class PackageEngineException implements Exception {
+  final String stderr;
+  PackageEngineException(this.stderr);
+
+  @override
+  String toString() => stderr.isEmpty ? 'dnf failed to run' : stderr;
+}
+
 class DeploymentInfo {
   final String version;
   final String checksum;
@@ -81,10 +93,24 @@ class OstreeService {
   }
 
   /// Unprivileged existence check so typos surface before escalating to
-  /// pkexec. Matches on exact name or name.arch.
+  /// pkexec. Matches on exact name or name.arch, then falls back to
+  /// `--whatprovides` so virtual names like "vim" (satisfied by
+  /// vim-enhanced etc., never a package themselves) check out the same way
+  /// `rpm-ostree install` would actually resolve them. A nonzero exit means
+  /// dnf itself failed to run (e.g. a broken plugin) rather than "not
+  /// found", so that's thrown instead of silently reported as false.
   static Future<bool> checkPackageExists(String name) async {
-    final result = await Process.run('dnf', ['repoquery', name]);
-    return result.exitCode == 0 && (result.stdout as String).trim().isNotEmpty;
+    final byName = await Process.run('dnf', ['repoquery', name]);
+    if (byName.exitCode != 0) {
+      throw PackageEngineException((byName.stderr as String).trim());
+    }
+    if ((byName.stdout as String).trim().isNotEmpty) return true;
+
+    final byProvides = await Process.run('dnf', ['repoquery', '--whatprovides', name]);
+    if (byProvides.exitCode != 0) {
+      throw PackageEngineException((byProvides.stderr as String).trim());
+    }
+    return (byProvides.stdout as String).trim().isNotEmpty;
   }
 
   /// Permanently layers a package via `rpm-ostree install`. Streams combined

lib/wizard_page.dart

@@ -20,6 +20,7 @@ class _WizardHomePageState extends State<WizardHomePage> {
   Future<DeploymentInfo>? _statusFuture;
   bool _checking = false;
   String? _checkError;
+  bool _checkErrorIsEngineFailure = false;
   bool _packageVerified = false;
 
   _ApplyState _applyState = _ApplyState.idle;
@@ -39,6 +40,7 @@ class _WizardHomePageState extends State<WizardHomePage> {
     setState(() {
       _checking = true;
       _checkError = null;
+      _checkErrorIsEngineFailure = false;
       _packageVerified = false;
     });
     try {
@@ -47,6 +49,12 @@ class _WizardHomePageState extends State<WizardHomePage> {
         _packageVerified = exists;
         _checkError = exists ? null : 'No package named "$name" was found.';
       });
+    } on PackageEngineException catch (e) {
+      setState(() {
+        _checkErrorIsEngineFailure = true;
+        _checkError = 'Package search isn\'t working right now, so this '
+            'can\'t be verified: $e';
+      });
     } catch (e) {
       setState(() => _checkError = e.toString());
     } finally {
@@ -220,7 +228,20 @@ class _WizardHomePageState extends State<WizardHomePage> {
         if (_checkError != null)
           Padding(
             padding: const EdgeInsets.only(top: 8),
-            child: Text(_checkError!, style: TextStyle(color: Theme.of(context).colorScheme.error)),
+            child: Row(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Icon(
+                  _checkErrorIsEngineFailure ? Icons.warning_amber : Icons.info_outline,
+                  color: Theme.of(context).colorScheme.error,
+                  size: 18,
+                ),
+                const SizedBox(width: 6),
+                Expanded(
+                  child: Text(_checkError!, style: TextStyle(color: Theme.of(context).colorScheme.error)),
+                ),
+              ],
+            ),
           ),
       ],
     );