feat: agent completion events + plugin hooks

spawnAgent() now writes completion events to events.jsonl.
Plugin hooks check for completions on:
- SessionStart: report agents that finished since last session
- Notification(idle_prompt): check when Claude is idle

Event format: {"type":"agent_completed","agent":"...","workspace":"...","timestamp":"..."}

Co-Authored-By: Virgil <virgil@lethean.io>

claude/core/hooks.json

@@ -91,6 +91,28 @@
           }
         ],
         "description": "Restore recent session context on startup"
+      },
+      {
+        "matcher": "*",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "${CLAUDE_PLUGIN_ROOT}/scripts/check-completions.sh"
+          }
+        ],
+        "description": "Report agent completions from previous session"
+      }
+    ],
+    "Notification": [
+      {
+        "matcher": "idle_prompt",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "${CLAUDE_PLUGIN_ROOT}/scripts/check-completions.sh"
+          }
+        ],
+        "description": "Check for agent completions when idle"
       }
     ]
   }

claude/core/scripts/check-completions.sh

@@ -0,0 +1,47 @@
+#!/bin/bash
+# Check for agent completion events since last check.
+# Called by plugin hooks to notify the orchestrating agent.
+
+EVENTS_FILE="$HOME/Code/host-uk/core/.core/workspace/events.jsonl"
+MARKER_FILE="$HOME/Code/host-uk/core/.core/workspace/.events-read"
+
+if [ ! -f "$EVENTS_FILE" ]; then
+    exit 0
+fi
+
+# Get events newer than last read
+if [ -f "$MARKER_FILE" ]; then
+    LAST_READ=$(cat "$MARKER_FILE")
+    NEW_EVENTS=$(awk -v ts="$LAST_READ" '$0 ~ "timestamp" && $0 > ts' "$EVENTS_FILE" 2>/dev/null)
+else
+    NEW_EVENTS=$(cat "$EVENTS_FILE")
+fi
+
+if [ -z "$NEW_EVENTS" ]; then
+    exit 0
+fi
+
+# Update marker
+date -u +%Y-%m-%dT%H:%M:%SZ > "$MARKER_FILE"
+
+# Count completions
+COUNT=$(echo "$NEW_EVENTS" | grep -c "agent_completed")
+
+if [ "$COUNT" -gt 0 ]; then
+    # Format for hook output
+    AGENTS=$(echo "$NEW_EVENTS" | grep "agent_completed" | python3 -c "
+import sys, json
+events = [json.loads(l) for l in sys.stdin if l.strip()]
+for e in events:
+    print(f\"  {e.get('agent','?')} — {e.get('workspace','?')}\")
+" 2>/dev/null)
+
+    cat << EOF
+{
+  "hookSpecificOutput": {
+    "hookEventName": "Notification",
+    "additionalContext": "$COUNT agent(s) completed:\n$AGENTS\n\nRun /core:status to review."
+  }
+}
+EOF
+fi

pkg/agentic/dispatch.go

@@ -121,6 +121,9 @@ func (s *PrepSubsystem) spawnAgent(agent, prompt, wsDir, srcDir string) (int, st
 			writeStatus(wsDir, st)
 		}
 
+		// Emit completion event
+		emitCompletionEvent(agent, filepath.Base(wsDir))
+
 		// Ingest scan findings as issues
 		s.ingestFindings(wsDir)
 

pkg/agentic/events.go

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: EUPL-1.2
+
+package agentic
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"time"
+
+	coreio "forge.lthn.ai/core/go-io"
+)
+
+// CompletionEvent is emitted when a dispatched agent finishes.
+// Written to ~/.core/workspace/events.jsonl as append-only log.
+type CompletionEvent struct {
+	Type      string `json:"type"`
+	Agent     string `json:"agent"`
+	Workspace string `json:"workspace"`
+	Status    string `json:"status"`
+	Timestamp string `json:"timestamp"`
+}
+
+// emitCompletionEvent appends a completion event to the events log.
+// The plugin's hook watches this file to notify the orchestrating agent.
+func emitCompletionEvent(agent, workspace string) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return
+	}
+
+	eventsFile := filepath.Join(home, "Code", "host-uk", "core", ".core", "workspace", "events.jsonl")
+
+	event := CompletionEvent{
+		Type:      "agent_completed",
+		Agent:     agent,
+		Workspace: workspace,
+		Status:    "completed",
+		Timestamp: time.Now().UTC().Format(time.RFC3339),
+	}
+
+	data, err := json.Marshal(event)
+	if err != nil {
+		return
+	}
+
+	// Append to events log
+	existing, _ := coreio.Local.Read(eventsFile)
+	coreio.Local.Write(eventsFile, existing+string(data)+"\n")
+}