feat(cli): clide instances / instance verbs for instance discovery (T-247)

Closes the observability half of T-247: a way to find and identify running
clides. `clide instances` scans the runtime socket dir, probes each live
*.sock, and prints its identity (version/pid/workspace/socketPath) as jsonl;
dead sockets are skipped. `clide instance` reports the one you're connected
to. Combined with CLIDE_SOCK honoring (this same ticket), you can now list
instances and pin the CLI to a chosen one.

Server: a new `instance` dispatcher command (registered in buildDispatcher
with the live workspace/pid/socket) returns the identity map; added to the
argv translator's umbrella set so a bare `instance` token routes to it.
Client: a POSIX dir-scan in clide.c (Windows stub until it ships).

Tests: e2e `instances` lists the live test server with its identity; a
cc-free unit test covers the `instance` command shape.

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

lib/main.dart

@@ -32,14 +32,16 @@ import 'package:clide/builtin/vim/vim.dart';
 import 'package:clide/builtin/tickets/tickets.dart';
 import 'package:clide/builtin/todos/todos.dart';
 import 'package:clide/builtin/welcome/welcome.dart';
-import 'dart:io' show Directory, File, Platform;
+import 'dart:io' show Directory, File, Platform, pid;
 
 import 'package:clide/kernel/kernel.dart';
+import 'package:clide/clide.dart' show clideVersion;
 import 'package:clide/src/daemon/dispatcher.dart';
 import 'package:clide/src/daemon/editor_commands.dart';
 import 'package:clide/src/daemon/files_commands.dart';
 import 'package:clide/src/daemon/git_commands.dart';
 import 'package:clide/src/daemon/image_commands.dart';
+import 'package:clide/src/daemon/instance_command.dart';
 import 'package:clide/src/daemon/log_commands.dart';
 import 'package:clide/src/daemon/pane_commands.dart';
 import 'package:clide/src/daemon/status_command.dart';
@@ -286,6 +288,10 @@ Future<void> main() async {
     // visible to `pane list` by snapshotting the kernel PanelRegistry +
     // LayoutArrangement at request time — no mirrored state to drift.
     registerPaneCommands(dispatcher, paneRegistry, viewPanes: () => snapshotViewPanes(panels, arrangement));
+    // `clide instance` — this instance's identity (version/pid/workspace/socket)
+    // so `clide instances` can list every live instance and a human/agent can
+    // tell which one a socket belongs to (T-247).
+    registerInstanceCommand(dispatcher, version: clideVersion, pid: pid, workspace: workRoot.path, socketPath: workspaceSocketPath(workRoot.path));
     // `clide log level [<level>]` — the live verbosity toggle's CLI half (T-433,
     // D-6 parity with the output-dock Level chip). Persists via the kernel
     // settings, captured post-boot.

lib/src/cli/argv_to_request.dart

@@ -27,7 +27,7 @@ import 'package:clide/src/ipc/schema_v1.dart';
 /// split. Match the IDs the dispatcher exposes directly. `tail` and
 /// `events` are handled by the IPC server itself (streaming / cursor-pull
 /// event reads, T-129 / T-223) rather than the dispatcher.
-const Set<String> _umbrellaCommands = {'status', 'tail', 'events', 'version', 'ping', 'capabilities'};
+const Set<String> _umbrellaCommands = {'status', 'tail', 'events', 'version', 'ping', 'capabilities', 'instance'};
 
 /// Sealed result of translating argv. Caller (the IPC server, or the
 /// C client wrapper in T-126) handles either branch.

lib/src/daemon/instance_command.dart

@@ -0,0 +1,16 @@
+/// Registers the `instance` command — this running clide's identity in one
+/// round-trip (T-247): version, pid, workspace root, and socket path. It's the
+/// per-instance metadata the `clide instances` CLI verb aggregates (by probing
+/// every live socket in the runtime dir), and it lets a human or agent confirm
+/// *which* instance a given socket belongs to.
+///
+/// Thin + Flutter-free: the caller (main.dart) passes the values it already
+/// holds at dispatcher-build time, so this stays trivially testable.
+library;
+
+import '../ipc/envelope.dart';
+import 'dispatcher.dart';
+
+void registerInstanceCommand(DaemonDispatcher d, {required String version, required int pid, required String workspace, required String socketPath}) {
+  d.register('instance', (req) async => IpcResponse.ok(id: req.id, data: {'version': version, 'pid': pid, 'workspace': workspace, 'socketPath': socketPath}));
+}