diff --git a/.claude/settings.json b/.claude/settings.json
index bac52e64..f6f82c6b 100644
--- a/.claude/settings.json
+++ b/.claude/settings.json
@@ -3,6 +3,28 @@
     "allow": [
       "Bash(git add *)",
       "Bash(git commit *)",
+      "Bash(git status *)",
+      "Bash(git diff *)",
+      "Bash(git log *)",
+      "Bash(git show *)",
+      "Bash(git branch *)",
+      "Bash(git checkout *)",
+      "Bash(git switch *)",
+      "Bash(git merge *)",
+      "Bash(git rebase *)",
+      "Bash(git stash *)",
+      "Bash(git fetch *)",
+      "Bash(git pull *)",
+      "Bash(git push *)",
+      "Bash(git tag *)",
+      "Bash(git remote *)",
+      "Bash(git rev-parse *)",
+      "Bash(git symbolic-ref *)",
+      "Bash(git ls-remote *)",
+      "Bash(git config *)",
+      "Bash(git blame *)",
+      "Bash(git shortlog *)",
+      "Bash(git cherry-pick *)",
       "Bash(dart *)",
       "Bash(flutter *)",
       "Bash(make *)",
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 51f277cd..bc9740f9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,23 @@ heading, and (b) bumping `project.yaml` `version:` in the same commit.
 - `Bash(pql)` and `Bash(pql *)` permissions in
   `.claude/settings.json`.
 
+- pql daemon subsystem (`lib/src/pql/`). `PqlClient` wraps the pql
+  CLI per D-003. IPC verbs `pql.files | meta | backlinks | outlinks
+  | tags | schema | query | doctor | decisions.sync | decisions.list
+  | decisions.show | decisions.coverage | tickets.list | tickets.show
+  | tickets.board | plan.status`. 15 new core tests.
+
+- `builtin.pql` — sidebar panel with four views: Files (pql-indexed
+  file listing), Query (PQL DSL input + results), Decisions (synced
+  D/Q/R records colour-coded by type), Tickets (kanban board columns).
+  Context panel tab showing backlinks + outlinks for the active file,
+  auto-refreshing on `editor.active-changed` events.
+
+- `builtin.problems` — sidebar panel aggregating diagnostics from
+  `pql.doctor` and `pql.decisions.sync`. Surfaces missing index DB,
+  stale skill installs, and broken decision cross-references with
+  actionable hints.
+
 - Git subsystem in the daemon (`lib/src/git/`). Status parser
   (`git status --porcelain`), unified-diff parser, and operations
   (stage, unstage, stage-hunk, discard, commit, stash, log, pull,
diff --git a/app/lib/builtin/pql/pql.dart b/app/lib/builtin/pql/pql.dart
index b968b883..fca71c8b 100644
--- a/app/lib/builtin/pql/pql.dart
+++ b/app/lib/builtin/pql/pql.dart
@@ -1 +1,5 @@
+export 'src/backlinks_controller.dart';
+export 'src/backlinks_view.dart';
 export 'src/extension.dart';
+export 'src/pql_controller.dart';
+export 'src/pql_panel_view.dart';
diff --git a/app/lib/builtin/pql/src/backlinks_controller.dart b/app/lib/builtin/pql/src/backlinks_controller.dart
new file mode 100644
index 00000000..b2aad7e4
--- /dev/null
+++ b/app/lib/builtin/pql/src/backlinks_controller.dart
@@ -0,0 +1,73 @@
+/// Tracks the active file and fetches its backlinks + outlinks
+/// from pql. Subscribes to editor.active-changed to auto-refresh.
+library;
+
+import 'dart:async';
+
+import 'package:clide_app/kernel/kernel.dart';
+import 'package:flutter/foundation.dart';
+
+class BacklinksController extends ChangeNotifier {
+  BacklinksController({required this.ipc, required this.events}) {
+    _eventSub = events.on<DaemonEvent>().listen(_onEvent);
+  }
+
+  final DaemonClient ipc;
+  final EventBus events;
+
+  StreamSubscription<DaemonEvent>? _eventSub;
+
+  String? _activePath;
+  String? get activePath => _activePath;
+
+  List<Map<String, Object?>> _backlinks = const [];
+  List<Map<String, Object?>> get backlinks => _backlinks;
+
+  List<Map<String, Object?>> _outlinks = const [];
+  List<Map<String, Object?>> get outlinks => _outlinks;
+
+  bool _loading = false;
+  bool get loading => _loading;
+
+  String? _error;
+  String? get error => _error;
+
+  Future<void> loadForPath(String path) async {
+    _activePath = path;
+    _loading = true;
+    _error = null;
+    notifyListeners();
+
+    final bl = await ipc.request('pql.backlinks', args: {'path': path});
+    final ol = await ipc.request('pql.outlinks', args: {'path': path});
+
+    _loading = false;
+    _backlinks = bl.ok ? _castList(bl.data['links']) : const [];
+    _outlinks = ol.ok ? _castList(ol.data['links']) : const [];
+    if (!bl.ok && !ol.ok) {
+      _error = bl.error?.message ?? 'backlinks failed';
+    }
+    notifyListeners();
+  }
+
+  void _onEvent(DaemonEvent e) {
+    if (e.subsystem != 'editor') return;
+    if (e.kind != 'editor.active-changed') return;
+    final path = e.data['path'] as String?;
+    if (path != null && path != _activePath) {
+      unawaited(loadForPath(path));
+    }
+  }
+
+  static List<Map<String, Object?>> _castList(Object? raw) {
+    if (raw is! List) return const [];
+    return [for (final e in raw) (e as Map).cast<String, Object?>()];
+  }
+
+  @override
+  void dispose() {
+    _eventSub?.cancel();
+    _eventSub = null;
+    super.dispose();
+  }
+}
diff --git a/app/lib/builtin/pql/src/backlinks_view.dart b/app/lib/builtin/pql/src/backlinks_view.dart
new file mode 100644
index 00000000..10de2fb0
--- /dev/null
+++ b/app/lib/builtin/pql/src/backlinks_view.dart
@@ -0,0 +1,198 @@
+/// Context panel showing backlinks and outlinks for the active file.
+library;
+
+import 'dart:async';
+
+import 'package:clide_app/kernel/kernel.dart';
+import 'package:clide_app/widgets/widgets.dart';
+import 'package:flutter/widgets.dart';
+
+import 'backlinks_controller.dart';
+
+class BacklinksView extends StatefulWidget {
+  const BacklinksView({super.key});
+
+  @override
+  State<BacklinksView> createState() => _BacklinksViewState();
+}
+
+class _BacklinksViewState extends State<BacklinksView> {
+  BacklinksController? _controller;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    if (_controller != null) return;
+    final kernel = ClideKernel.of(context);
+    _controller = BacklinksController(ipc: kernel.ipc, events: kernel.events);
+  }
+
+  @override
+  void dispose() {
+    _controller?.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final c = _controller;
+    if (c == null) return const SizedBox.shrink();
+    return ListenableBuilder(
+      listenable: c,
+      builder: (context, _) {
+        final tokens = ClideTheme.of(context).surface;
+        if (c.activePath == null) {
+          return const Padding(
+            padding: EdgeInsets.all(12),
+            child: ClideText(
+              'Open a file to see its links.',
+              muted: true,
+              fontSize: 12,
+            ),
+          );
+        }
+        return Semantics(
+          label: 'backlinks for ${c.activePath}',
+          container: true,
+          explicitChildNodes: true,
+          child: SingleChildScrollView(
+            padding: const EdgeInsets.symmetric(vertical: 4),
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.stretch,
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                Padding(
+                  padding: const EdgeInsets.symmetric(
+                      horizontal: 12, vertical: 4),
+                  child: ClideText(
+                    c.activePath!.split('/').last,
+                    fontSize: 12,
+                    color: tokens.globalForeground,
+                  ),
+                ),
+                if (c.error != null)
+                  Padding(
+                    padding: const EdgeInsets.symmetric(
+                        horizontal: 12, vertical: 4),
+                    child: ClideText(
+                      c.error!,
+                      color: tokens.statusError,
+                      fontSize: 11,
+                    ),
+                  ),
+                if (c.loading)
+                  const Padding(
+                    padding: EdgeInsets.all(12),
+                    child: ClideText('Loading…', muted: true, fontSize: 12),
+                  ),
+                _LinkGroup(
+                  label: 'Backlinks',
+                  links: c.backlinks,
+                  pathKey: 'source',
+                ),
+                _LinkGroup(
+                  label: 'Outlinks',
+                  links: c.outlinks,
+                  pathKey: 'target',
+                ),
+              ],
+            ),
+          ),
+        );
+      },
+    );
+  }
+}
+
+class _LinkGroup extends StatelessWidget {
+  const _LinkGroup({
+    required this.label,
+    required this.links,
+    required this.pathKey,
+  });
+
+  final String label;
+  final List<Map<String, Object?>> links;
+  final String pathKey;
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      crossAxisAlignment: CrossAxisAlignment.stretch,
+      mainAxisSize: MainAxisSize.min,
+      children: [
+        Padding(
+          padding:
+              const EdgeInsets.only(left: 12, right: 8, top: 8, bottom: 2),
+          child: ClideText(
+            '$label (${links.length})',
+            fontSize: 11,
+            muted: true,
+          ),
+        ),
+        if (links.isEmpty)
+          const Padding(
+            padding: EdgeInsets.symmetric(horizontal: 20, vertical: 2),
+            child: ClideText('None', fontSize: 11, muted: true),
+          ),
+        for (final link in links)
+          _LinkRow(link: link, pathKey: pathKey),
+      ],
+    );
+  }
+}
+
+class _LinkRow extends StatefulWidget {
+  const _LinkRow({required this.link, required this.pathKey});
+  final Map<String, Object?> link;
+  final String pathKey;
+
+  @override
+  State<_LinkRow> createState() => _LinkRowState();
+}
+
+class _LinkRowState extends State<_LinkRow> {
+  bool _hover = false;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    final target = widget.link[widget.pathKey] as String? ?? '';
+    final alias = widget.link['alias'] as String?;
+    final display = alias ?? target;
+
+    return MouseRegion(
+      cursor: SystemMouseCursors.click,
+      onEnter: (_) => setState(() => _hover = true),
+      onExit: (_) => setState(() => _hover = false),
+      child: GestureDetector(
+        behavior: HitTestBehavior.opaque,
+        onTap: () {
+          if (!target.startsWith('http')) {
+            final kernel = ClideKernel.of(context);
+            unawaited(
+                kernel.ipc.request('editor.open', args: {'path': target}));
+          }
+        },
+        child: Semantics(
+          button: true,
+          label: target,
+          child: Container(
+            color: _hover ? tokens.sidebarItemHover : null,
+            padding:
+                const EdgeInsets.symmetric(horizontal: 20, vertical: 2),
+            child: ClideText(
+              display,
+              fontSize: 12,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              color: target.startsWith('http')
+                  ? tokens.statusInfo
+                  : tokens.sidebarForeground,
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
diff --git a/app/lib/builtin/pql/src/extension.dart b/app/lib/builtin/pql/src/extension.dart
index cd118ae4..075c07a7 100644
--- a/app/lib/builtin/pql/src/extension.dart
+++ b/app/lib/builtin/pql/src/extension.dart
@@ -1,17 +1,37 @@
+import 'package:clide_app/builtin/pql/src/backlinks_view.dart';
+import 'package:clide_app/builtin/pql/src/pql_panel_view.dart';
 import 'package:clide_app/extension/extension.dart';
+import 'package:clide_app/kernel/kernel.dart';
 
-/// Tier-0 stub. Real implementation lands in a later tier; the extension
-/// is registered so the extensions-ui surface can list it as "installed,
-/// not yet implemented" and its id is reserved.
 class PqlExtension extends ClideExtension {
   @override
   String get id => 'builtin.pql';
   @override
   String get title => 'pql';
   @override
-  String get version => '0.0.0-stub';
+  String get version => '0.1.0';
   @override
   List<String> get dependsOn => const [];
+
   @override
-  List<ContributionPoint> get contributions => const [];
+  List<ContributionPoint> get contributions => [
+        TabContribution(
+          id: 'pql.panel',
+          slot: Slots.sidebar,
+          title: 'pql',
+          titleKey: 'tab.title',
+          i18nNamespace: id,
+          priority: -60,
+          build: (_) => const PqlPanelView(),
+        ),
+        TabContribution(
+          id: 'pql.backlinks',
+          slot: Slots.contextPanel,
+          title: 'Links',
+          titleKey: 'tab.links',
+          i18nNamespace: id,
+          priority: -80,
+          build: (_) => const BacklinksView(),
+        ),
+      ];
 }
diff --git a/app/lib/builtin/pql/src/pql_controller.dart b/app/lib/builtin/pql/src/pql_controller.dart
new file mode 100644
index 00000000..b7a6d0d6
--- /dev/null
+++ b/app/lib/builtin/pql/src/pql_controller.dart
@@ -0,0 +1,147 @@
+/// State model for the pql sidebar panel.
+///
+/// Manages schema cache, query execution, file listing, and
+/// decision/ticket views. All data comes through pql.* IPC verbs.
+library;
+
+import 'dart:async';
+
+import 'package:clide_app/kernel/kernel.dart';
+import 'package:flutter/foundation.dart';
+
+enum PqlView { files, query, decisions, tickets }
+
+class PqlController extends ChangeNotifier {
+  PqlController({required this.ipc});
+
+  final DaemonClient ipc;
+
+  PqlView _view = PqlView.files;
+  PqlView get view => _view;
+
+  String? _error;
+  String? get error => _error;
+
+  bool _loading = false;
+  bool get loading => _loading;
+
+  List<Map<String, Object?>> _results = const [];
+  List<Map<String, Object?>> get results => _results;
+
+  Map<String, Object?> _planStatus = const {};
+  Map<String, Object?> get planStatus => _planStatus;
+
+  void switchView(PqlView v) {
+    if (_view == v) return;
+    _view = v;
+    _results = const [];
+    _error = null;
+    notifyListeners();
+    switch (v) {
+      case PqlView.files:
+        unawaited(loadFiles());
+      case PqlView.decisions:
+        unawaited(loadDecisions());
+      case PqlView.tickets:
+        unawaited(loadTickets());
+      case PqlView.query:
+        break;
+    }
+  }
+
+  Future<void> loadFiles({String? glob}) async {
+    _loading = true;
+    notifyListeners();
+
+    final r = await ipc.request('pql.files', args: {
+      if (glob != null) 'glob': glob,
+      'limit': 200,
+    });
+
+    _loading = false;
+    if (!r.ok) {
+      _error = r.error?.message;
+      notifyListeners();
+      return;
+    }
+    _error = null;
+    _results = _castList(r.data['files']);
+    notifyListeners();
+  }
+
+  Future<void> runQuery(String dsl) async {
+    if (dsl.trim().isEmpty) return;
+    _loading = true;
+    _error = null;
+    notifyListeners();
+
+    final r = await ipc.request('pql.query', args: {
+      'query': dsl,
+      'limit': 200,
+    });
+
+    _loading = false;
+    if (!r.ok) {
+      _error = r.error?.message;
+      _results = const [];
+      notifyListeners();
+      return;
+    }
+    _results = _castList(r.data['results']);
+    notifyListeners();
+  }
+
+  Future<void> loadDecisions() async {
+    _loading = true;
+    notifyListeners();
+
+    await ipc.request('pql.decisions.sync');
+    final r = await ipc.request('pql.decisions.list');
+
+    _loading = false;
+    if (!r.ok) {
+      _error = r.error?.message;
+      notifyListeners();
+      return;
+    }
+    _error = null;
+    _results = _castList(r.data['decisions']);
+    notifyListeners();
+  }
+
+  Future<void> loadTickets() async {
+    _loading = true;
+    notifyListeners();
+
+    final r = await ipc.request('pql.tickets.board');
+
+    _loading = false;
+    if (!r.ok) {
+      _error = r.error?.message;
+      notifyListeners();
+      return;
+    }
+    _error = null;
+    _results = _castList(r.data['columns']);
+    notifyListeners();
+  }
+
+  Future<void> loadPlanStatus() async {
+    final r = await ipc.request('pql.plan.status');
+    if (r.ok) {
+      _planStatus = r.data;
+      notifyListeners();
+    }
+  }
+
+  void clearError() {
+    if (_error == null) return;
+    _error = null;
+    notifyListeners();
+  }
+
+  static List<Map<String, Object?>> _castList(Object? raw) {
+    if (raw is! List) return const [];
+    return [for (final e in raw) (e as Map).cast<String, Object?>()];
+  }
+}
diff --git a/app/lib/builtin/pql/src/pql_panel_view.dart b/app/lib/builtin/pql/src/pql_panel_view.dart
new file mode 100644
index 00000000..cba8e718
--- /dev/null
+++ b/app/lib/builtin/pql/src/pql_panel_view.dart
@@ -0,0 +1,379 @@
+/// Sidebar panel for pql — file listing, DSL query input,
+/// decisions list, and ticket board views.
+library;
+
+import 'dart:async';
+
+import 'package:clide_app/kernel/kernel.dart';
+import 'package:clide_app/widgets/widgets.dart';
+import 'package:flutter/widgets.dart';
+
+import 'pql_controller.dart';
+
+class PqlPanelView extends StatefulWidget {
+  const PqlPanelView({super.key});
+
+  @override
+  State<PqlPanelView> createState() => _PqlPanelViewState();
+}
+
+class _PqlPanelViewState extends State<PqlPanelView> {
+  PqlController? _controller;
+  final TextEditingController _queryInput = TextEditingController();
+  final FocusNode _queryFocus = FocusNode();
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    if (_controller != null) return;
+    final kernel = ClideKernel.of(context);
+    _controller = PqlController(ipc: kernel.ipc);
+    unawaited(_controller!.loadFiles());
+  }
+
+  @override
+  void dispose() {
+    _controller?.dispose();
+    _queryInput.dispose();
+    _queryFocus.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final c = _controller;
+    if (c == null) return const SizedBox.shrink();
+    return ListenableBuilder(
+      listenable: c,
+      builder: (context, _) {
+        final tokens = ClideTheme.of(context).surface;
+        return Semantics(
+          label: 'pql panel',
+          container: true,
+          explicitChildNodes: true,
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.stretch,
+            children: [
+              _ViewTabs(controller: c),
+              if (c.view == PqlView.query)
+                _QueryInput(
+                  input: _queryInput,
+                  focus: _queryFocus,
+                  controller: c,
+                ),
+              if (c.error != null)
+                Padding(
+                  padding: const EdgeInsets.symmetric(
+                      horizontal: 12, vertical: 4),
+                  child: ClideText(
+                    c.error!,
+                    color: tokens.statusError,
+                    fontSize: 11,
+                    maxLines: 3,
+                  ),
+                ),
+              if (c.loading && c.results.isEmpty)
+                const Padding(
+                  padding: EdgeInsets.all(12),
+                  child: ClideText('Loading…', muted: true, fontSize: 12),
+                ),
+              if (!c.loading && c.results.isEmpty && c.error == null)
+                const Padding(
+                  padding: EdgeInsets.all(12),
+                  child: ClideText('No results.', muted: true, fontSize: 12),
+                ),
+              Expanded(
+                child: SingleChildScrollView(
+                  padding: const EdgeInsets.symmetric(vertical: 4),
+                  child: Column(
+                    crossAxisAlignment: CrossAxisAlignment.stretch,
+                    mainAxisSize: MainAxisSize.min,
+                    children: [
+                      if (c.view == PqlView.files)
+                        for (final f in c.results) _FileRow(entry: f),
+                      if (c.view == PqlView.query)
+                        for (final r in c.results) _QueryResultRow(entry: r),
+                      if (c.view == PqlView.decisions)
+                        for (final d in c.results) _DecisionRow(entry: d),
+                      if (c.view == PqlView.tickets)
+                        for (final col in c.results) _TicketColumn(column: col),
+                    ],
+                  ),
+                ),
+              ),
+            ],
+          ),
+        );
+      },
+    );
+  }
+}
+
+class _ViewTabs extends StatelessWidget {
+  const _ViewTabs({required this.controller});
+  final PqlController controller;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    return Container(
+      padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 4),
+      decoration: BoxDecoration(
+        border: Border(bottom: BorderSide(color: tokens.panelBorder)),
+      ),
+      child: Row(
+        children: [
+          for (final v in PqlView.values)
+            Padding(
+              padding: const EdgeInsets.only(right: 8),
+              child: Semantics(
+                button: true,
+                toggled: controller.view == v,
+                label: v.name,
+                child: GestureDetector(
+                  onTap: () => controller.switchView(v),
+                  child: MouseRegion(
+                    cursor: SystemMouseCursors.click,
+                    child: ClideText(
+                      _tabLabel(v),
+                      fontSize: 11,
+                      color: controller.view == v
+                          ? tokens.globalForeground
+                          : tokens.globalTextMuted,
+                    ),
+                  ),
+                ),
+              ),
+            ),
+        ],
+      ),
+    );
+  }
+
+  static String _tabLabel(PqlView v) => switch (v) {
+        PqlView.files => 'Files',
+        PqlView.query => 'Query',
+        PqlView.decisions => 'Decisions',
+        PqlView.tickets => 'Tickets',
+      };
+}
+
+class _QueryInput extends StatelessWidget {
+  const _QueryInput({
+    required this.input,
+    required this.focus,
+    required this.controller,
+  });
+
+  final TextEditingController input;
+  final FocusNode focus;
+  final PqlController controller;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    return Padding(
+      padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 4),
+      child: Semantics(
+        label: 'pql query',
+        textField: true,
+        child: Container(
+          decoration: BoxDecoration(
+            border: Border.all(color: tokens.globalBorder),
+          ),
+          padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 4),
+          child: EditableText(
+            controller: input,
+            focusNode: focus,
+            style: TextStyle(
+              fontFamily: clideMonoFamily,
+              fontSize: 12,
+              color: tokens.globalForeground,
+            ),
+            cursorColor: tokens.globalFocus,
+            backgroundCursorColor: tokens.globalFocus,
+            maxLines: 1,
+            onSubmitted: (_) =>
+                unawaited(controller.runQuery(input.text)),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+class _FileRow extends StatefulWidget {
+  const _FileRow({required this.entry});
+  final Map<String, Object?> entry;
+
+  @override
+  State<_FileRow> createState() => _FileRowState();
+}
+
+class _FileRowState extends State<_FileRow> {
+  bool _hover = false;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    final path = widget.entry['path'] as String? ?? '';
+    final name = widget.entry['name'] as String? ?? path.split('/').last;
+    return MouseRegion(
+      cursor: SystemMouseCursors.click,
+      onEnter: (_) => setState(() => _hover = true),
+      onExit: (_) => setState(() => _hover = false),
+      child: GestureDetector(
+        behavior: HitTestBehavior.opaque,
+        onTap: () {
+          final kernel = ClideKernel.of(context);
+          unawaited(
+              kernel.ipc.request('editor.open', args: {'path': path}));
+        },
+        child: Semantics(
+          button: true,
+          label: 'Open $name',
+          child: Container(
+            color: _hover ? tokens.sidebarItemHover : null,
+            padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 3),
+            child: ClideText(
+              path,
+              fontSize: 12,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              color: tokens.sidebarForeground,
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+class _QueryResultRow extends StatelessWidget {
+  const _QueryResultRow({required this.entry});
+  final Map<String, Object?> entry;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    final name = entry['name'] as String? ?? entry['path'] as String? ?? '';
+    final values = entry.entries
+        .where((e) => e.key != 'name' && e.key != 'path')
+        .map((e) => '${e.key}: ${e.value}')
+        .join(' · ');
+    return Padding(
+      padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 2),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        mainAxisSize: MainAxisSize.min,
+        children: [
+          ClideText(name, fontSize: 12, color: tokens.sidebarForeground),
+          if (values.isNotEmpty)
+            ClideText(values, fontSize: 10, muted: true, maxLines: 2),
+        ],
+      ),
+    );
+  }
+}
+
+class _DecisionRow extends StatelessWidget {
+  const _DecisionRow({required this.entry});
+  final Map<String, Object?> entry;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    final id = entry['id'] as String? ?? '';
+    final title = entry['title'] as String? ?? '';
+    final type = entry['type'] as String? ?? '';
+    final domain = entry['domain'] as String? ?? '';
+
+    final Color idColor = switch (type) {
+      'confirmed' => tokens.statusSuccess,
+      'question' => tokens.statusWarning,
+      'rejected' => tokens.statusError,
+      _ => tokens.sidebarForeground,
+    };
+
+    return Padding(
+      padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 2),
+      child: Row(
+        children: [
+          SizedBox(
+            width: 44,
+            child: ClideText(id, fontSize: 11, color: idColor,
+                fontFamily: clideMonoFamily),
+          ),
+          const SizedBox(width: 4),
+          Expanded(
+            child: ClideText(
+              title,
+              fontSize: 12,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              color: tokens.sidebarForeground,
+            ),
+          ),
+          ClideText(domain, fontSize: 10, muted: true),
+        ],
+      ),
+    );
+  }
+}
+
+class _TicketColumn extends StatelessWidget {
+  const _TicketColumn({required this.column});
+  final Map<String, Object?> column;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    final status = column['status'] as String? ?? '';
+    final tickets = (column['tickets'] as List?) ?? const [];
+    if (tickets.isEmpty) return const SizedBox.shrink();
+
+    return Column(
+      crossAxisAlignment: CrossAxisAlignment.stretch,
+      mainAxisSize: MainAxisSize.min,
+      children: [
+        Padding(
+          padding:
+              const EdgeInsets.only(left: 12, right: 8, top: 8, bottom: 2),
+          child: ClideText(
+            '$status (${tickets.length})',
+            fontSize: 11,
+            muted: true,
+          ),
+        ),
+        for (final t in tickets)
+          Padding(
+            padding:
+                const EdgeInsets.symmetric(horizontal: 20, vertical: 2),
+            child: Row(
+              children: [
+                SizedBox(
+                  width: 44,
+                  child: ClideText(
+                    (t as Map)['id'] as String? ?? '',
+                    fontSize: 11,
+                    fontFamily: clideMonoFamily,
+                    color: tokens.statusInfo,
+                  ),
+                ),
+                const SizedBox(width: 4),
+                Expanded(
+                  child: ClideText(
+                    t['title'] as String? ?? '',
+                    fontSize: 12,
+                    maxLines: 1,
+                    overflow: TextOverflow.ellipsis,
+                    color: tokens.sidebarForeground,
+                  ),
+                ),
+              ],
+            ),
+          ),
+      ],
+    );
+  }
+}
diff --git a/app/lib/builtin/problems/problems.dart b/app/lib/builtin/problems/problems.dart
index b968b883..cd4ffed1 100644
--- a/app/lib/builtin/problems/problems.dart
+++ b/app/lib/builtin/problems/problems.dart
@@ -1 +1,3 @@
 export 'src/extension.dart';
+export 'src/problems_controller.dart';
+export 'src/problems_view.dart';
diff --git a/app/lib/builtin/problems/src/extension.dart b/app/lib/builtin/problems/src/extension.dart
index 7337459b..107e1d2e 100644
--- a/app/lib/builtin/problems/src/extension.dart
+++ b/app/lib/builtin/problems/src/extension.dart
@@ -1,17 +1,27 @@
+import 'package:clide_app/builtin/problems/src/problems_view.dart';
 import 'package:clide_app/extension/extension.dart';
+import 'package:clide_app/kernel/kernel.dart';
 
-/// Tier-0 stub. Real implementation lands in a later tier; the extension
-/// is registered so the extensions-ui surface can list it as "installed,
-/// not yet implemented" and its id is reserved.
 class ProblemsExtension extends ClideExtension {
   @override
   String get id => 'builtin.problems';
   @override
   String get title => 'Problems';
   @override
-  String get version => '0.0.0-stub';
+  String get version => '0.1.0';
   @override
-  List<String> get dependsOn => const [];
+  List<String> get dependsOn => const ['builtin.pql'];
+
   @override
-  List<ContributionPoint> get contributions => const [];
+  List<ContributionPoint> get contributions => [
+        TabContribution(
+          id: 'problems.panel',
+          slot: Slots.sidebar,
+          title: 'Problems',
+          titleKey: 'tab.title',
+          i18nNamespace: id,
+          priority: -50,
+          build: (_) => const ProblemsView(),
+        ),
+      ];
 }
diff --git a/app/lib/builtin/problems/src/problems_controller.dart b/app/lib/builtin/problems/src/problems_controller.dart
new file mode 100644
index 00000000..540a1950
--- /dev/null
+++ b/app/lib/builtin/problems/src/problems_controller.dart
@@ -0,0 +1,102 @@
+/// State model for the problems panel.
+///
+/// Aggregates diagnostic information from pql.doctor and
+/// pql.decisions.validate (via pql.decisions.sync which reports
+/// broken refs). Refreshes on demand.
+library;
+
+import 'dart:async';
+
+import 'package:clide_app/kernel/kernel.dart';
+import 'package:flutter/foundation.dart';
+
+class Problem {
+  const Problem({required this.source, required this.message, this.hint});
+  final String source;
+  final String message;
+  final String? hint;
+
+  Map<String, Object?> toJson() => {
+        'source': source,
+        'message': message,
+        if (hint != null) 'hint': hint,
+      };
+}
+
+class ProblemsController extends ChangeNotifier {
+  ProblemsController({required this.ipc});
+
+  final DaemonClient ipc;
+
+  List<Problem> _problems = const [];
+  List<Problem> get problems => _problems;
+
+  bool _loading = false;
+  bool get loading => _loading;
+
+  String? _error;
+  String? get error => _error;
+
+  Future<void> refresh() async {
+    _loading = true;
+    notifyListeners();
+
+    final found = <Problem>[];
+
+    final doctor = await ipc.request('pql.doctor');
+    if (doctor.ok) {
+      final db = (doctor.data['db'] as Map?)?.cast<String, Object?>();
+      if (db != null && db['exists'] == false) {
+        found.add(const Problem(
+          source: 'pql',
+          message: 'pql index database not found',
+          hint: 'Run pql to build the index.',
+        ));
+      }
+      final skill = (doctor.data['skill'] as Map?)?.cast<String, Object?>();
+      if (skill != null) {
+        final project =
+            (skill['project'] as Map?)?.cast<String, Object?>();
+        if (project != null) {
+          final state = project['state'] as String?;
+          if (state == 'stale') {
+            found.add(const Problem(
+              source: 'pql',
+              message: 'pql skill is stale — newer version available',
+              hint: 'Run: pql skill install',
+            ));
+          } else if (state == 'missing') {
+            found.add(const Problem(
+              source: 'pql',
+              message: 'pql skill not installed',
+              hint: 'Run: pql init --with-skill=yes',
+            ));
+          }
+        }
+      }
+    } else {
+      found.add(Problem(
+        source: 'pql',
+        message: 'pql doctor failed',
+        hint: doctor.error?.message,
+      ));
+    }
+
+    final sync = await ipc.request('pql.decisions.sync');
+    if (sync.ok) {
+      final broken = (sync.data['broken'] as num?)?.toInt() ?? 0;
+      if (broken > 0) {
+        found.add(Problem(
+          source: 'decisions',
+          message: '$broken broken cross-reference(s) in decisions/',
+          hint: 'Run: pql decisions validate',
+        ));
+      }
+    }
+
+    _loading = false;
+    _error = null;
+    _problems = found;
+    notifyListeners();
+  }
+}
diff --git a/app/lib/builtin/problems/src/problems_view.dart b/app/lib/builtin/problems/src/problems_view.dart
new file mode 100644
index 00000000..53cf0c16
--- /dev/null
+++ b/app/lib/builtin/problems/src/problems_view.dart
@@ -0,0 +1,162 @@
+/// Sidebar panel showing project diagnostics from pql.
+library;
+
+import 'dart:async';
+
+import 'package:clide_app/kernel/kernel.dart';
+import 'package:clide_app/widgets/widgets.dart';
+import 'package:flutter/widgets.dart';
+
+import 'problems_controller.dart';
+
+class ProblemsView extends StatefulWidget {
+  const ProblemsView({super.key});
+
+  @override
+  State<ProblemsView> createState() => _ProblemsViewState();
+}
+
+class _ProblemsViewState extends State<ProblemsView> {
+  ProblemsController? _controller;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    if (_controller != null) return;
+    final kernel = ClideKernel.of(context);
+    _controller = ProblemsController(ipc: kernel.ipc);
+    unawaited(_controller!.refresh());
+  }
+
+  @override
+  void dispose() {
+    _controller?.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final c = _controller;
+    if (c == null) return const SizedBox.shrink();
+    return ListenableBuilder(
+      listenable: c,
+      builder: (context, _) {
+        final tokens = ClideTheme.of(context).surface;
+        return Semantics(
+          label: 'problems panel',
+          container: true,
+          explicitChildNodes: true,
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.stretch,
+            children: [
+              Padding(
+                padding: const EdgeInsets.symmetric(
+                    horizontal: 12, vertical: 6),
+                child: Row(
+                  children: [
+                    Expanded(
+                      child: ClideText(
+                        'Problems (${c.problems.length})',
+                        fontSize: 12,
+                        color: tokens.sidebarForeground,
+                      ),
+                    ),
+                    Semantics(
+                      button: true,
+                      label: 'refresh problems',
+                      child: GestureDetector(
+                        onTap: () => unawaited(c.refresh()),
+                        child: MouseRegion(
+                          cursor: SystemMouseCursors.click,
+                          child: ClideText(
+                            'Refresh',
+                            fontSize: 10,
+                            color: tokens.sidebarForeground,
+                          ),
+                        ),
+                      ),
+                    ),
+                  ],
+                ),
+              ),
+              if (c.loading && c.problems.isEmpty)
+                const Padding(
+                  padding: EdgeInsets.all(12),
+                  child: ClideText('Scanning…', muted: true, fontSize: 12),
+                ),
+              if (!c.loading && c.problems.isEmpty)
+                const Padding(
+                  padding: EdgeInsets.all(12),
+                  child: ClideText(
+                    'No problems found.',
+                    muted: true,
+                    fontSize: 12,
+                  ),
+                ),
+              Expanded(
+                child: SingleChildScrollView(
+                  padding: const EdgeInsets.symmetric(vertical: 4),
+                  child: Column(
+                    crossAxisAlignment: CrossAxisAlignment.stretch,
+                    mainAxisSize: MainAxisSize.min,
+                    children: [
+                      for (final p in c.problems) _ProblemRow(problem: p),
+                    ],
+                  ),
+                ),
+              ),
+            ],
+          ),
+        );
+      },
+    );
+  }
+}
+
+class _ProblemRow extends StatelessWidget {
+  const _ProblemRow({required this.problem});
+  final Problem problem;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    return Padding(
+      padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 4),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        mainAxisSize: MainAxisSize.min,
+        children: [
+          Row(
+            children: [
+              ClideText(
+                problem.source,
+                fontSize: 10,
+                color: tokens.statusWarning,
+                fontFamily: clideMonoFamily,
+              ),
+              const SizedBox(width: 6),
+              Expanded(
+                child: ClideText(
+                  problem.message,
+                  fontSize: 12,
+                  color: tokens.sidebarForeground,
+                  maxLines: 2,
+                ),
+              ),
+            ],
+          ),
+          if (problem.hint != null)
+            Padding(
+              padding: const EdgeInsets.only(left: 44, top: 2),
+              child: ClideText(
+                problem.hint!,
+                fontSize: 10,
+                muted: true,
+                fontFamily: clideMonoFamily,
+              ),
+            ),
+        ],
+      ),
+    );
+  }
+}