feat: add multi-feature batching for coding agents

Enable the orchestrator to assign 1-3 features per coding agent subprocess,
selected via dependency chain extension + same-category fill. This reduces
cold-start overhead and leverages shared context across related features.

Orchestrator (parallel_orchestrator.py):
- Add batch tracking: _batch_features and _feature_to_primary data structures
- Add build_feature_batches() with dependency chain + category fill algorithm
- Add start_feature_batch() and _spawn_coding_agent_batch() methods
- Update _on_agent_complete() for batch cleanup across all features
- Update stop_feature() with _feature_to_primary lookup
- Update get_ready_features() to exclude all batch feature IDs
- Update main loop to build batches then spawn per available slot

CLI and agent layer:
- Add --feature-ids (comma-separated) and --batch-size CLI args
- Add feature_ids parameter to run_autonomous_agent() with batch prompt selection
- Add get_batch_feature_prompt() with sequential workflow instructions

WebSocket layer (server/websocket.py):
- Add BATCH_CODING_AGENT_START_PATTERN and BATCH_FEATURES_COMPLETE_PATTERN
- Add _handle_batch_agent_start() and _handle_batch_agent_complete() methods
- Add featureIds field to all agent_update messages
- Track current_feature_id updates as agent moves through batch

Frontend (React UI):
- Add featureIds to ActiveAgent and WSAgentUpdateMessage types
- Update KanbanColumn and DependencyGraph agent-feature maps for batch
- Update AgentCard to show "Batch: #X, #Y, #Z" with active feature highlight
- Add "Features per Agent" segmented control (1-3) in SettingsModal

Settings integration (full stack):
- Add batch_size to schemas, settings router, agent router, process manager
- Default batch_size=3, user-configurable 1-3 via settings UI
- batch_size=1 is functionally identical to pre-batching behavior

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ui/src/components/AgentCard.tsx

@@ -112,12 +112,25 @@ export function AgentCard({ agent, onShowLogs }: AgentCardProps) {
 
         {/* Feature info */}
         <div>
-          <div className="text-xs text-muted-foreground mb-0.5">
-            Feature #{agent.featureId}
-          </div>
-          <div className="text-sm font-medium truncate" title={agent.featureName}>
-            {agent.featureName}
-          </div>
+          {agent.featureIds && agent.featureIds.length > 1 ? (
+            <>
+              <div className="text-xs text-muted-foreground mb-0.5">
+                Batch: {agent.featureIds.map(id => `#${id}`).join(', ')}
+              </div>
+              <div className="text-sm font-bold truncate">
+                Active: Feature #{agent.featureId}
+              </div>
+            </>
+          ) : (
+            <>
+              <div className="text-xs text-muted-foreground mb-0.5">
+                Feature #{agent.featureId}
+              </div>
+              <div className="text-sm font-medium truncate" title={agent.featureName}>
+                {agent.featureName}
+              </div>
+            </>
+          )}
         </div>
 
         {/* Thought bubble */}
@@ -195,7 +208,10 @@ export function AgentLogModal({ agent, logs, onClose }: AgentLogModalProps) {
                 </Badge>
               </div>
               <p className="text-sm text-muted-foreground">
-                Feature #{agent.featureId}: {agent.featureName}
+                {agent.featureIds && agent.featureIds.length > 1
+                  ? `Batch: ${agent.featureIds.map(id => `#${id}`).join(', ')}`
+                  : `Feature #${agent.featureId}: ${agent.featureName}`
+                }
               </p>
             </div>
           </div>

ui/src/components/DependencyGraph.tsx

@@ -227,10 +227,14 @@ function DependencyGraphInner({ graphData, onNodeClick, activeAgents = [] }: Dep
   }, [])
 
   // Create a map of featureId to agent info for quick lookup
+  // Maps ALL batch feature IDs to the same agent
   const agentByFeatureId = useMemo(() => {
     const map = new Map<number, NodeAgentInfo>()
     for (const agent of activeAgents) {
-      map.set(agent.featureId, { name: agent.agentName, state: agent.state })
+      const ids = agent.featureIds || [agent.featureId]
+      for (const fid of ids) {
+        map.set(fid, { name: agent.agentName, state: agent.state })
+      }
     }
     return map
   }, [activeAgents])

ui/src/components/KanbanColumn.tsx

@@ -41,9 +41,14 @@ export function KanbanColumn({
   showCreateSpec,
 }: KanbanColumnProps) {
   // Create a map of feature ID to active agent for quick lookup
-  const agentByFeatureId = new Map(
-    activeAgents.map(agent => [agent.featureId, agent])
-  )
+  // Maps ALL batch feature IDs to the same agent
+  const agentByFeatureId = new Map<number, ActiveAgent>()
+  for (const agent of activeAgents) {
+    const ids = agent.featureIds || [agent.featureId]
+    for (const fid of ids) {
+      agentByFeatureId.set(fid, agent)
+    }
+  }
 
   return (
     <Card className={`overflow-hidden ${colorMap[color]} py-0`}>

ui/src/components/SettingsModal.tsx

@@ -41,6 +41,12 @@ export function SettingsModal({ isOpen, onClose }: SettingsModalProps) {
     }
   }
 
+  const handleBatchSizeChange = (size: number) => {
+    if (!updateSettings.isPending) {
+      updateSettings.mutate({ batch_size: size })
+    }
+  }
+
   const models = modelsData?.models ?? []
   const isSaving = updateSettings.isPending
 
@@ -234,6 +240,30 @@ export function SettingsModal({ isOpen, onClose }: SettingsModalProps) {
               </div>
             </div>
 
+            {/* Features per Agent */}
+            <div className="space-y-2">
+              <Label className="font-medium">Features per Agent</Label>
+              <p className="text-sm text-muted-foreground">
+                Number of features assigned to each coding agent
+              </p>
+              <div className="flex rounded-lg border overflow-hidden">
+                {[1, 2, 3].map((size) => (
+                  <button
+                    key={size}
+                    onClick={() => handleBatchSizeChange(size)}
+                    disabled={isSaving}
+                    className={`flex-1 py-2 px-3 text-sm font-medium transition-colors ${
+                      (settings.batch_size ?? 1) === size
+                        ? 'bg-primary text-primary-foreground'
+                        : 'bg-background text-foreground hover:bg-muted'
+                    } ${isSaving ? 'opacity-50 cursor-not-allowed' : ''}`}
+                  >
+                    {size}
+                  </button>
+                ))}
+              </div>
+            </div>
+
             {/* Update Error */}
             {updateSettings.isError && (
               <Alert variant="destructive">

ui/src/hooks/useProjects.ts

@@ -267,6 +267,7 @@ const DEFAULT_SETTINGS: Settings = {
   ollama_mode: false,
   testing_agent_ratio: 1,
   playwright_headless: true,
+  batch_size: 3,
 }
 
 export function useAvailableModels() {

ui/src/hooks/useWebSocket.ts

@@ -210,6 +210,7 @@ export function useProjectWebSocket(projectName: string | null) {
                     agentName: message.agentName,
                     agentType: message.agentType || 'coding',  // Default to coding for backwards compat
                     featureId: message.featureId,
+                    featureIds: message.featureIds || [message.featureId],
                     featureName: message.featureName,
                     state: message.state,
                     thought: message.thought,
@@ -225,6 +226,7 @@ export function useProjectWebSocket(projectName: string | null) {
                       agentName: message.agentName,
                       agentType: message.agentType || 'coding',  // Default to coding for backwards compat
                       featureId: message.featureId,
+                      featureIds: message.featureIds || [message.featureId],
                       featureName: message.featureName,
                       state: message.state,
                       thought: message.thought,

ui/src/lib/types.ts

@@ -199,7 +199,8 @@ export interface ActiveAgent {
   agentIndex: number  // -1 for synthetic completions
   agentName: AgentMascot | 'Unknown'
   agentType: AgentType  // "coding" or "testing"
-  featureId: number
+  featureId: number        // Current/primary feature (backward compat)
+  featureIds: number[]     // All features in batch
   featureName: string
   state: AgentState
   thought?: string
@@ -270,6 +271,7 @@ export interface WSAgentUpdateMessage {
   agentName: AgentMascot | 'Unknown'
   agentType: AgentType  // "coding" or "testing"
   featureId: number
+  featureIds?: number[]  // All features in batch (may be absent for backward compat)
   featureName: string
   state: AgentState
   thought?: string
@@ -530,6 +532,7 @@ export interface Settings {
   ollama_mode: boolean
   testing_agent_ratio: number  // Regression testing agents (0-3)
   playwright_headless: boolean
+  batch_size: number  // Features per coding agent batch (1-3)
 }
 
 export interface SettingsUpdate {
@@ -537,6 +540,7 @@ export interface SettingsUpdate {
   model?: string
   testing_agent_ratio?: number
   playwright_headless?: boolean
+  batch_size?: number
 }
 
 export interface ProjectSettingsUpdate {