MAESTRO: fix(hooks): add session-complete handler to enable orphan reaper cleanup

Cherry-picked from PR #844 by @thusdigital. Sessions stayed in active
sessions map forever after summarize, causing the orphan reaper to think
all processes were still active. Adds session-complete as Stop phase 2
hook that calls POST /api/sessions/complete to remove sessions from the
active map, allowing the reaper to correctly identify and clean up
orphaned worker processes. Fixes #842.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/handlers/session-complete.ts

@@ -0,0 +1,62 @@
+/**
+ * Session Complete Handler - Stop (Phase 2)
+ *
+ * Completes the session after summarize has been queued.
+ * This removes the session from the active sessions map, allowing
+ * the orphan reaper to clean up any remaining subprocess.
+ *
+ * Fixes Issue #842: Orphan reaper starts but never reaps because
+ * sessions stay in the active sessions map forever.
+ */
+
+import type { EventHandler, NormalizedHookInput, HookResult } from '../types.js';
+import { ensureWorkerRunning, getWorkerPort } from '../../shared/worker-utils.js';
+import { logger } from '../../utils/logger.js';
+
+export const sessionCompleteHandler: EventHandler = {
+  async execute(input: NormalizedHookInput): Promise<HookResult> {
+    // Ensure worker is running
+    await ensureWorkerRunning();
+
+    const { sessionId } = input;
+    const port = getWorkerPort();
+
+    if (!sessionId) {
+      logger.warn('HOOK', 'session-complete: Missing sessionId, skipping');
+      return { continue: true, suppressOutput: true };
+    }
+
+    logger.info('HOOK', '→ session-complete: Removing session from active map', {
+      workerPort: port,
+      contentSessionId: sessionId
+    });
+
+    try {
+      // Call the session complete endpoint by contentSessionId
+      const response = await fetch(`http://127.0.0.1:${port}/api/sessions/complete`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          contentSessionId: sessionId
+        })
+      });
+
+      if (!response.ok) {
+        const text = await response.text();
+        logger.warn('HOOK', 'session-complete: Failed to complete session', {
+          status: response.status,
+          body: text
+        });
+      } else {
+        logger.info('HOOK', 'Session completed successfully', { contentSessionId: sessionId });
+      }
+    } catch (error) {
+      // Log but don't fail - session may already be gone
+      logger.warn('HOOK', 'session-complete: Error completing session', {
+        error: (error as Error).message
+      });
+    }
+
+    return { continue: true, suppressOutput: true };
+  }
+};