T-129: event streaming over the socket — clide tail --events

Sixth slice of T-99. Long-lived event subscription path, the second
half of D-6.

Wire shape:
- Client sends `{cmd:"tail", args:{flags:{events:true, filter:X}}}`.
- Server responds with `{ok:true, data:{streaming:true, filter:X}}`.
- Server pushes `{type:"event", subsystem, kind, ts, data}` lines
  until the client closes.

Server (lib/src/ipc/server.dart):
- Takes a DaemonBus, subscribes to DaemonEvent on start.
- Per-subsystem ring buffer (replayDepth=16 per D-6) populated on
  every emit.
- `tail --events` connection: send ack, replay matching events from
  ring, register the client for future fanout.
- _argv envelope now unwrapped at the server layer so the streaming
  check sees the inner `tail` cmd (not just `_argv`).
- Broken subscriber writes drop the subscriber cleanly; the bus
  doesn't block on a stalled client.

Client (native/clide-cli/clide.c):
- Sniffs `data.streaming:true` in the ack. If set, loops reading
  JSON-line events to stdout (with fflush per line) until EOF.

Tests:
- test/ipc/server_streaming_test.dart — 8 cases covering ack shape,
  filter, replay buffer (size + ordering), multi-subscriber fanout,
  broken-subscriber cleanup.
- test/cli/clide_cli_e2e_test.dart gets a tail --events test that
  spawns the C client, emits two events on the bus, asserts they
  print on stdout.

T-99 children remaining: T-130 (MCP), T-131 (wrap-up).

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

test/cli/clide_cli_e2e_test.dart

@@ -11,6 +11,8 @@ library;
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:clide/kernel/src/events/bus.dart';
+import 'package:clide/kernel/src/events/types.dart';
 import 'package:clide/kernel/src/log.dart';
 import 'package:clide/src/cli/argv_dispatch.dart';
 import 'package:clide/src/daemon/dispatcher.dart';
@@ -25,6 +27,7 @@ void main() {
   late final Directory workspaceRoot;
   late final IpcServer server;
   late final DaemonDispatcher dispatcher;
+  late final DaemonBus streamingBus;
 
   setUpAll(() async {
     final repoRoot = Directory.current.path;
@@ -52,10 +55,12 @@ void main() {
     Directory('${workspaceRoot.path}/.git').createSync();
     dispatcher = DaemonDispatcher();
     registerArgvUnwrap(dispatcher);
+    streamingBus = DaemonBus();
     server = IpcServer(
       dispatcher: dispatcher,
       workspaceRoot: workspaceRoot.path,
       log: Logger(minLevel: LogLevel.error, sinks: const []),
+      events: streamingBus,
     );
     await server.start();
   });
@@ -65,6 +70,7 @@ void main() {
     try {
       await server.stop();
     } catch (_) {}
+    await streamingBus.dispose();
     if (workspaceRoot.existsSync()) {
       workspaceRoot.deleteSync(recursive: true);
     }
@@ -134,5 +140,36 @@ void main() {
       expect(r.exitCode, isNot(0));
       expect(r.stderr.toString(), isNotEmpty);
     });
+
+    test('tail --events streams bus events to stdout (T-129)', () async {
+      if (!hasCC) {
+        markTestSkipped('cc not available');
+        return;
+      }
+      final proc = await Process.start(binaryPath, ['tail', '--events', '--filter', 'pane'], workingDirectory: workspaceRoot.path);
+      addTearDown(() => proc.kill());
+      final lines = <String>[];
+      final sub = proc.stdout.transform(utf8.decoder).transform(const LineSplitter()).listen(lines.add);
+      addTearDown(sub.cancel);
+      // Wait for the ack so the server has registered us.
+      var attempts = 0;
+      while (lines.isEmpty && attempts < 50) {
+        await Future<void>.delayed(const Duration(milliseconds: 20));
+        attempts++;
+      }
+      expect(lines, isNotEmpty, reason: 'no ack received');
+      // Emit two events.
+      streamingBus.emit(DaemonEvent(subsystem: 'pane', kind: 'spawned', data: const {'id': 'p1'}, ts: DateTime.now().toUtc()));
+      streamingBus.emit(DaemonEvent(subsystem: 'pane', kind: 'closed', data: const {'id': 'p1'}, ts: DateTime.now().toUtc()));
+      attempts = 0;
+      while (lines.length < 3 && attempts < 100) {
+        await Future<void>.delayed(const Duration(milliseconds: 20));
+        attempts++;
+      }
+      expect(lines.length, greaterThanOrEqualTo(3), reason: 'expected ack + 2 events, got: $lines');
+      final concatenated = lines.skip(1).join('\n');
+      expect(concatenated, contains('"kind":"spawned"'));
+      expect(concatenated, contains('"kind":"closed"'));
+    });
   });
 }