surface Claude Code Workflow runs in convo + sidebar (T-416)

A `Workflow` tool-use launches its multi-agent run in the background and
returns immediately; the real fan-out arrives out-of-band on stream-json
`type:"system"` task_* events (task_started / task_progress / task_updated /
task_notification) keyed by the launching tool-use id — which clide was
dropping. (Wire shape captured by two live stream-json probes; recorded on
the ticket.)

- workflow_run.dart: a pure, Flutter-free WorkflowRun/WorkflowAgent model
  that folds those events (phases, per-agent start→progress→done deltas,
  usage) into a snapshot.
- StreamJsonSession recognises the events, accumulates a
  Map<toolUseId, WorkflowRun>, and exposes `workflows` + `workflowsStream`.
- A `Workflow` tool-use with a live run renders a dedicated run card —
  phase groups, per-agent rows with spinner/check status, usage, and the
  script — falling back to the generic tool card pre-progress or on reload.
  The run breaks the activity cluster so it's always first-class (like T-342).
- The sidebar Activity tab adds a WORKFLOWS section: one row per run with its
  done/total agent count, tinted by running/done state.

Closes T-416 and the T-410 epic (all children done).

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

lib/builtin/claude/src/stream_json_session.dart

@@ -19,6 +19,7 @@ import 'dart:convert';
 import 'dart:io';
 
 import 'package:clide/builtin/claude/src/transcript_reader.dart';
+import 'package:clide/builtin/claude/src/workflow_run.dart';
 import 'package:clide/src/util/value_stream.dart';
 
 /// The claude subprocess, abstracted so tests drive it without spawning.
@@ -377,6 +378,20 @@ class StreamJsonSession {
   Map<String, bool> get toolUseOutcomes => _toolUseOutcome;
   Set<String> get quietErrorToolUseIds => _quietErrorToolUses;
 
+  /// Live Workflow runs, keyed by their launching `Workflow` tool-use id
+  /// (T-416). Accumulated from the out-of-band `system` task_* events the
+  /// harness emits while a workflow runs in the background; the conversation
+  /// card and the sidebar indicator both read this snapshot. Ephemeral — the
+  /// events aren't in the resumed transcript, so this is empty on reload.
+  final _workflows = <String, WorkflowRun>{};
+  final _workflowsCtl = ValueStream<Map<String, WorkflowRun>>.seeded(const {});
+
+  /// The current workflow runs, keyed by launching tool-use id.
+  Map<String, WorkflowRun> get workflows => Map.unmodifiable(_workflows);
+
+  /// Emits the workflow-run map whenever a `system` task event updates it.
+  Stream<Map<String, WorkflowRun>> get workflowsStream => _workflowsCtl.stream;
+
   /// Whether a turn is in flight (between a send and claude's `result`). Drives
   /// the composer's Stop affordance.
   bool _busy = false;
@@ -501,6 +516,15 @@ class StreamJsonSession {
       return;
     }
 
+    // Workflow run progress (T-416): the harness reports a backgrounded Workflow
+    // tool's fan-out on out-of-band `system` task_* events keyed by the
+    // launching tool-use id. Fold them into the run snapshot and notify; they
+    // carry no conversation item, so don't fall through to the parser.
+    if (isWorkflowSystemEvent(ev)) {
+      _onWorkflowEvent(ev);
+      return;
+    }
+
     // Finalise a streamed reply: when the real text `assistant` event for a
     // message we streamed arrives, reuse the placeholder's `partial-<id>` uuid
     // so the controller replaces the placeholder in place rather than appending
@@ -574,6 +598,15 @@ class StreamJsonSession {
     }
   }
 
+  /// Fold one workflow `system` task event into its run snapshot, keyed by the
+  /// launching tool-use id, and publish the updated map (T-416).
+  void _onWorkflowEvent(Map<String, dynamic> ev) {
+    final id = ev['tool_use_id'] as String;
+    final prior = _workflows[id] ?? WorkflowRun(toolUseId: id);
+    _workflows[id] = prior.foldEvent(ev);
+    _workflowsCtl.add(Map.unmodifiable(_workflows));
+  }
+
   /// Handle an inbound `control_request`. `can_use_tool` becomes a [ToolPrompt]
   /// item the UI resolves; every other subtype is answered with an error so
   /// the turn never hangs waiting on us (D-78).
@@ -938,6 +971,7 @@ class StreamJsonSession {
     await _proc.kill();
     await _items.close();
     await _statusCtl.close();
+    await _workflowsCtl.close();
     await _sessionIdCtl.close();
     await _pendingCtl.close();
     await _busyCtl.close();