add LogRing — bounded retention for Logger records (T-54)

The Logger only live-broadcasts; an output panel opening late would see no
history. LogRing is a drop-oldest sink (default 2000 records) that keeps the
recent window plus per-source and per-level bookkeeping — distinct sources
for the panel's filter dropdown, level counts for the status-bar health
badge. Flutter-free; the dock UI wraps it. First slice of the D-87 dock.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/kernel/log_ring_test.dart

@@ -0,0 +1,94 @@
+/// T-54: LogRing — bounded drop-oldest retention for Logger records, with
+/// per-source / per-level bookkeeping for the panel filter + status badge.
+library;
+
+import 'package:clide/kernel/src/log.dart';
+import 'package:clide/kernel/src/log_ring.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+LogRecord _rec(LogLevel level, String source, String message) =>
+    LogRecord(level: level, source: source, message: message, timestamp: DateTime.utc(2026, 6, 6));
+
+void main() {
+  test('retains records in arrival order', () {
+    final ring = LogRing(capacity: 10);
+    ring
+      ..add(_rec(LogLevel.info, 'ipc', 'a'))
+      ..add(_rec(LogLevel.info, 'mcp', 'b'));
+    expect(ring.records.map((r) => r.message), ['a', 'b']);
+    expect(ring.length, 2);
+  });
+
+  test('drops oldest past capacity', () {
+    final ring = LogRing(capacity: 3);
+    for (final m in ['a', 'b', 'c', 'd', 'e']) {
+      ring.add(_rec(LogLevel.info, 'ipc', m));
+    }
+    expect(ring.records.map((r) => r.message), ['c', 'd', 'e']);
+  });
+
+  test('sources are distinct, sorted, and shrink as records age out', () {
+    final ring = LogRing(capacity: 2);
+    ring
+      ..add(_rec(LogLevel.info, 'git', '1'))
+      ..add(_rec(LogLevel.info, 'ipc', '2'));
+    expect(ring.sources, ['git', 'ipc']);
+    // Pushing past capacity evicts the 'git' record → 'git' leaves the set.
+    ring.add(_rec(LogLevel.info, 'pql', '3'));
+    expect(ring.sources, ['ipc', 'pql']);
+  });
+
+  test('countAtLeast totals retained records at a level or higher', () {
+    final ring = LogRing(capacity: 10);
+    ring
+      ..add(_rec(LogLevel.debug, 'x', 'd'))
+      ..add(_rec(LogLevel.info, 'x', 'i'))
+      ..add(_rec(LogLevel.warn, 'x', 'w'))
+      ..add(_rec(LogLevel.error, 'x', 'e'));
+    expect(ring.countAtLeast(LogLevel.warn), 2); // warn + error
+    expect(ring.countAtLeast(LogLevel.error), 1);
+    expect(ring.countAtLeast(LogLevel.trace), 4);
+  });
+
+  test('eviction decrements level counts', () {
+    final ring = LogRing(capacity: 2);
+    ring
+      ..add(_rec(LogLevel.error, 'x', 'e1'))
+      ..add(_rec(LogLevel.info, 'x', 'i'))
+      ..add(_rec(LogLevel.info, 'x', 'i2')); // evicts the error
+    expect(ring.countAtLeast(LogLevel.error), 0);
+  });
+
+  test('clear empties records, sources, and counts', () {
+    final ring = LogRing(capacity: 10);
+    ring
+      ..add(_rec(LogLevel.warn, 'pql', 'w'))
+      ..clear();
+    expect(ring.isEmpty, isTrue);
+    expect(ring.sources, isEmpty);
+    expect(ring.countAtLeast(LogLevel.trace), 0);
+  });
+
+  test('changes fires on add and on clear', () async {
+    final ring = LogRing(capacity: 10);
+    final events = <void>[];
+    final sub = ring.changes.listen(events.add);
+    ring.add(_rec(LogLevel.info, 'x', 'a'));
+    ring.clear();
+    await Future<void>.delayed(Duration.zero);
+    expect(events.length, 2);
+    await sub.cancel();
+    ring.dispose();
+  });
+
+  test('clear on an empty ring does not fire changes', () async {
+    final ring = LogRing(capacity: 10);
+    final events = <void>[];
+    final sub = ring.changes.listen(events.add);
+    ring.clear();
+    await Future<void>.delayed(Duration.zero);
+    expect(events, isEmpty);
+    await sub.cancel();
+    ring.dispose();
+  });
+}