feat(v2): add agent teams support with subagent pane spawning and routing

Detect subagent tool_call events (Agent/Task/dispatch_agent), auto-spawn
child agent panes with parent/child navigation. Messages with parentId
are routed to child panes; parent session keeps its own messages.

- agents.svelte.ts: parent/child hierarchy fields, findChildByToolUseId,
  getChildSessions, parent-aware createAgentSession/removeAgentSession
- agent-dispatcher.ts: SUBAGENT_TOOL_NAMES detection, toolUseToChildPane
  routing map, spawnSubagentPane with auto-grouping under parent title
- AgentPane.svelte: parent link bar (SUB badge), children bar (chips
  with status colors), clickable navigation between parent/child
- SessionList.svelte: subagent panes show arrow icon instead of asterisk

v2/src/lib/agent-dispatcher.ts

@@ -3,7 +3,7 @@
 
 import { onSidecarMessage, onSidecarExited, restartAgent, type SidecarMessage } from './adapters/agent-bridge';
 import { adaptSDKMessage } from './adapters/sdk-messages';
-import type { InitContent, CostContent } from './adapters/sdk-messages';
+import type { InitContent, CostContent, ToolCallContent } from './adapters/sdk-messages';
 import {
   updateAgentStatus,
   setAgentSdkSessionId,
@@ -11,7 +11,10 @@ import {
   appendAgentMessages,
   updateAgentCost,
   getAgentSessions,
+  createAgentSession,
+  findChildByToolUseId,
 } from './stores/agents.svelte';
+import { addPane, getPanes } from './stores/layout.svelte';
 import { notify } from './stores/notifications.svelte';
 
 let unlistenMsg: (() => void) | null = null;
@@ -100,10 +103,31 @@ export async function startAgentDispatcher(): Promise<void> {
   });
 }
 
+// Tool names that indicate a subagent spawn
+const SUBAGENT_TOOL_NAMES = new Set(['Agent', 'Task', 'dispatch_agent']);
+
+// Map toolUseId -> child session pane id for routing
+const toolUseToChildPane = new Map<string, string>();
+
 function handleAgentEvent(sessionId: string, event: Record<string, unknown>): void {
   const messages = adaptSDKMessage(event);
 
+  // Route messages with parentId to the appropriate child pane
+  const mainMessages: typeof messages = [];
+  const childBuckets = new Map<string, typeof messages>();
+
   for (const msg of messages) {
+    if (msg.parentId && toolUseToChildPane.has(msg.parentId)) {
+      const childPaneId = toolUseToChildPane.get(msg.parentId)!;
+      if (!childBuckets.has(childPaneId)) childBuckets.set(childPaneId, []);
+      childBuckets.get(childPaneId)!.push(msg);
+    } else {
+      mainMessages.push(msg);
+    }
+  }
+
+  // Process main session messages
+  for (const msg of mainMessages) {
     switch (msg.type) {
       case 'init': {
         const init = msg.content as InitContent;
@@ -112,6 +136,14 @@ function handleAgentEvent(sessionId: string, event: Record<string, unknown>): vo
         break;
       }
 
+      case 'tool_call': {
+        const tc = msg.content as ToolCallContent;
+        if (SUBAGENT_TOOL_NAMES.has(tc.name)) {
+          spawnSubagentPane(sessionId, tc);
+        }
+        break;
+      }
+
       case 'cost': {
         const cost = msg.content as CostContent;
         updateAgentCost(sessionId, {
@@ -133,9 +165,70 @@ function handleAgentEvent(sessionId: string, event: Record<string, unknown>): vo
     }
   }
 
-  if (messages.length > 0) {
-    appendAgentMessages(sessionId, messages);
+  if (mainMessages.length > 0) {
+    appendAgentMessages(sessionId, mainMessages);
   }
+
+  // Append messages to child panes and update their status
+  for (const [childPaneId, childMsgs] of childBuckets) {
+    for (const msg of childMsgs) {
+      if (msg.type === 'init') {
+        const init = msg.content as InitContent;
+        setAgentSdkSessionId(childPaneId, init.sessionId);
+        setAgentModel(childPaneId, init.model);
+        updateAgentStatus(childPaneId, 'running');
+      } else if (msg.type === 'cost') {
+        const cost = msg.content as CostContent;
+        updateAgentCost(childPaneId, {
+          costUsd: cost.totalCostUsd,
+          inputTokens: cost.inputTokens,
+          outputTokens: cost.outputTokens,
+          numTurns: cost.numTurns,
+          durationMs: cost.durationMs,
+        });
+        updateAgentStatus(childPaneId, cost.isError ? 'error' : 'done');
+      }
+    }
+    appendAgentMessages(childPaneId, childMsgs);
+  }
+}
+
+function spawnSubagentPane(parentSessionId: string, tc: ToolCallContent): void {
+  // Don't create duplicate pane for same tool_use
+  if (toolUseToChildPane.has(tc.toolUseId)) return;
+  const existing = findChildByToolUseId(parentSessionId, tc.toolUseId);
+  if (existing) {
+    toolUseToChildPane.set(tc.toolUseId, existing.id);
+    return;
+  }
+
+  const childId = crypto.randomUUID();
+  const prompt = typeof tc.input === 'object' && tc.input !== null
+    ? (tc.input as Record<string, unknown>).prompt as string ?? tc.name
+    : tc.name;
+  const label = typeof tc.input === 'object' && tc.input !== null
+    ? (tc.input as Record<string, unknown>).name as string ?? tc.name
+    : tc.name;
+
+  // Register routing
+  toolUseToChildPane.set(tc.toolUseId, childId);
+
+  // Create agent session with parent link
+  createAgentSession(childId, prompt, {
+    sessionId: parentSessionId,
+    toolUseId: tc.toolUseId,
+  });
+  updateAgentStatus(childId, 'running');
+
+  // Create layout pane, auto-grouped under parent's title
+  const parentPane = getPanes().find(p => p.id === parentSessionId);
+  const groupName = parentPane?.title ?? `Agent ${parentSessionId.slice(0, 8)}`;
+  addPane({
+    id: childId,
+    type: 'agent',
+    title: `Sub: ${label}`,
+    group: groupName,
+  });
 }
 
 export function stopAgentDispatcher(): void {

v2/src/lib/components/Agent/AgentPane.svelte

@@ -6,8 +6,10 @@
     getAgentSession,
     createAgentSession,
     removeAgentSession,
+    getChildSessions,
     type AgentSession,
   } from '../../stores/agents.svelte';
+  import { focusPane } from '../../stores/layout.svelte';
   import { isSidecarAlive, setSidecarAlive } from '../../agent-dispatcher';
   import AgentTree from './AgentTree.svelte';
   import { getHighlighter, highlightCode, escapeHtml } from '../../utils/highlight';
@@ -37,6 +39,8 @@
   let restarting = $state(false);
   let showTree = $state(false);
   let hasToolCalls = $derived(session?.messages.some(m => m.type === 'tool_call') ?? false);
+  let parentSession = $derived(session?.parentSessionId ? getAgentSession(session.parentSessionId) : undefined);
+  let childSessions = $derived(session ? getChildSessions(session.id) : []);
 
   const mdRenderer = new Renderer();
   mdRenderer.code = function({ text, lang }: { text: string; lang?: string }) {
@@ -188,6 +192,24 @@
       </form>
     </div>
   {:else}
+    {#if parentSession}
+      <div class="parent-link">
+        <span class="parent-badge">SUB</span>
+        <button class="parent-btn" onclick={() => focusPane(parentSession!.id)}>
+          ← {parentSession.prompt ? parentSession.prompt.slice(0, 40) : 'Parent agent'}
+        </button>
+      </div>
+    {/if}
+    {#if childSessions.length > 0}
+      <div class="children-bar">
+        <span class="children-label">{childSessions.length} subagent{childSessions.length > 1 ? 's' : ''}</span>
+        {#each childSessions as child (child.id)}
+          <button class="child-chip" class:running={child.status === 'running'} class:done={child.status === 'done'} class:error={child.status === 'error'} onclick={() => focusPane(child.id)}>
+            {child.prompt.slice(0, 20)}{child.prompt.length > 20 ? '...' : ''}
+          </button>
+        {/each}
+      </div>
+    {/if}
     {#if hasToolCalls}
       <div class="tree-toggle">
         <button class="tree-btn" onclick={() => showTree = !showTree}>
@@ -320,6 +342,71 @@
     font-size: 13px;
   }
 
+  .parent-link {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 4px 12px;
+    border-bottom: 1px solid var(--border);
+    flex-shrink: 0;
+    font-size: 11px;
+  }
+
+  .parent-badge {
+    background: var(--ctp-mauve);
+    color: var(--ctp-crust);
+    padding: 1px 5px;
+    border-radius: 3px;
+    font-size: 9px;
+    font-weight: 700;
+    letter-spacing: 0.5px;
+  }
+
+  .parent-btn {
+    background: none;
+    border: none;
+    color: var(--ctp-mauve);
+    cursor: pointer;
+    font-size: 11px;
+    padding: 0;
+    font-family: inherit;
+  }
+
+  .parent-btn:hover { color: var(--text-primary); text-decoration: underline; }
+
+  .children-bar {
+    display: flex;
+    align-items: center;
+    gap: 4px;
+    padding: 4px 12px;
+    border-bottom: 1px solid var(--border);
+    flex-shrink: 0;
+    flex-wrap: wrap;
+    font-size: 11px;
+  }
+
+  .children-label {
+    color: var(--text-muted);
+    font-size: 10px;
+    margin-right: 4px;
+  }
+
+  .child-chip {
+    background: var(--bg-surface);
+    border: 1px solid var(--border);
+    color: var(--text-secondary);
+    padding: 1px 6px;
+    border-radius: 3px;
+    font-size: 10px;
+    cursor: pointer;
+    font-family: inherit;
+  }
+
+  .child-chip:hover { color: var(--text-primary); border-color: var(--accent); }
+  .child-chip.running { border-color: var(--ctp-blue); color: var(--ctp-blue); }
+  .child-chip.done { border-color: var(--ctp-green); color: var(--ctp-green); }
+  .child-chip.error { border-color: var(--ctp-red); color: var(--ctp-red); }
+
   .tree-toggle {
     padding: 4px 12px;
     border-bottom: 1px solid var(--border);

v2/src/lib/components/Sidebar/SessionList.svelte

@@ -43,7 +43,8 @@
     }
   }
 
-  function paneIcon(type: string): string {
+  function paneIcon(type: string, title: string): string {
+    if (type === 'agent' && title.startsWith('Sub: ')) return '↳';
     switch (type) {
       case 'terminal': return '>';
       case 'agent': return '*';
@@ -153,7 +154,7 @@
       {#snippet paneItem(pane: Pane)}
         <li class="pane-item" class:focused={pane.focused}>
           <button class="pane-btn" onclick={() => focusPane(pane.id)} oncontextmenu={(e) => { e.preventDefault(); setGroup(pane.id); }}>
-            <span class="pane-icon">{paneIcon(pane.type)}</span>
+            <span class="pane-icon">{paneIcon(pane.type, pane.title)}</span>
             <span class="pane-name">{pane.title}</span>
           </button>
           <button class="remove-btn" onclick={() => removePane(pane.id)}>&times;</button>

v2/src/lib/stores/agents.svelte.ts

@@ -18,6 +18,10 @@ export interface AgentSession {
   numTurns: number;
   durationMs: number;
   error?: string;
+  // Agent Teams: parent/child hierarchy
+  parentSessionId?: string;
+  parentToolUseId?: string;
+  childSessionIds: string[];
 }
 
 let sessions = $state<AgentSession[]>([]);
@@ -30,7 +34,7 @@ export function getAgentSession(id: string): AgentSession | undefined {
   return sessions.find(s => s.id === id);
 }
 
-export function createAgentSession(id: string, prompt: string): void {
+export function createAgentSession(id: string, prompt: string, parent?: { sessionId: string; toolUseId: string }): void {
   sessions.push({
     id,
     status: 'starting',
@@ -41,7 +45,18 @@ export function createAgentSession(id: string, prompt: string): void {
     outputTokens: 0,
     numTurns: 0,
     durationMs: 0,
+    parentSessionId: parent?.sessionId,
+    parentToolUseId: parent?.toolUseId,
+    childSessionIds: [],
   });
+
+  // Register as child of parent
+  if (parent) {
+    const parentSession = sessions.find(s => s.id === parent.sessionId);
+    if (parentSession) {
+      parentSession.childSessionIds.push(id);
+    }
+  }
 }
 
 export function updateAgentStatus(id: string, status: AgentStatus, error?: string): void {
@@ -86,6 +101,24 @@ export function updateAgentCost(
   session.durationMs = cost.durationMs;
 }
 
+/** Find a child session that was spawned by a specific tool_use */
+export function findChildByToolUseId(parentId: string, toolUseId: string): AgentSession | undefined {
+  return sessions.find(s => s.parentSessionId === parentId && s.parentToolUseId === toolUseId);
+}
+
+/** Get all child sessions for a given parent */
+export function getChildSessions(parentId: string): AgentSession[] {
+  return sessions.filter(s => s.parentSessionId === parentId);
+}
+
 export function removeAgentSession(id: string): void {
+  // Also remove from parent's childSessionIds
+  const session = sessions.find(s => s.id === id);
+  if (session?.parentSessionId) {
+    const parent = sessions.find(s => s.id === session.parentSessionId);
+    if (parent) {
+      parent.childSessionIds = parent.childSessionIds.filter(cid => cid !== id);
+    }
+  }
   sessions = sessions.filter(s => s.id !== id);
 }