Task tool (subagents) not displayed with special treatment in app

Summary

When Claude uses the Task tool to spawn subagents (for research, exploration, etc.), the app displays them as regular tool cards instead of with a special "Thinking: description..." display that would match the Mac CLI's visual treatment of background agents.

Current Behavior

• Task tool appears as a generic tool card with the robot icon
• The tool input is shown as raw JSON (or parsed description)
• No visual indication that work is happening in the background
• No clear distinction from other tools like Read/Write/Bash

Expected Behavior

• Subagent invocations should show a distinctive UI:
• "Thinking: [task description]..." text
• The agent's prompt should be viewable (like thinking content)
• Visual indication of background activity
• Should match the StreamUpdateType.subagent handling that exists in the Dart code

Root Cause Analysis

The Dart code defines StreamUpdateType.subagent (in claude_tool_service.dart line 42), but the Rust engine only emits StreamUpdateType::ToolUse for all tool calls including Task.

The Rust parser (parser/types.rs) has no Subagent variant in its StreamUpdateType enum.

The _processStreamUpdate method in ssh_chat_screen.dart has a case StreamUpdateType.subagent: handler (lines 1999-2011) that would show the special display, but this code path is never reached because:

1. Rust emits ToolUse for Task tool
2. _convertUpdateType in engine_session_adapter.dart maps Rust ToolUse → Dart toolUse
3. The Dart subagent type is never used

Proposed Fix Options

Option A: Client-side detection (simpler)

In _processStreamUpdate or _convertEvent, check if toolName == "Task" and convert to StreamUpdateType.subagent:

// In engine_session_adapter.dart _convertEvent()
case StreamUpdateType.toolUse:
  final toolName = event.toolName ?? 'unknown';
  if (toolName == 'Task') {
    return ClaudeStreamUpdate(
      type: StreamUpdateType.subagent,  // Convert to subagent
      content: ...,
      metadata: {'description': input['description'], 'prompt': input['prompt']},
    );
  }
  // ... normal toolUse handling

Option B: Rust-side (more comprehensive)

Add StreamUpdateType::Subagent to the Rust enum and detect Task tool in the parser, emitting the new type.

Related

This is related to the thinking display improvements - both are about showing Claude's internal processes more clearly to the user.

Files Affected

• rust/src/parser/types.rs - StreamUpdateType enum
• lib/services/engine_session_adapter.dart - type conversion
• lib/screens/ssh_chat_screen.dart - existing subagent handler at line 1999