fix: EPYC cluster SSH timeout - increase timeout 30s→60s + add SSH options

CRITICAL FIX (Dec 1, 2025): Cluster start was failing with 'operation failed'

Problem:
- SSH commands timing out after 30s (too short for 2-hop SSH to worker2)
- Missing SSH options caused prompts/delays
- Result: Coordinator failed to start worker processes

Solution:
- Increased timeout from 30s to 60s for nested SSH hops
- Added SSH options: -o StrictHostKeyChecking=no -o ConnectTimeout=10
- Applied options to both ssh_command() and worker startup commands

Verification (Dec 1, 09:40):
- Worker1: 23 processes running (chunk 0-2000)
- Worker2: 24 processes running (chunk 2000-4000)
- Cluster status: ACTIVE with 2 workers
- Both chunks processing successfully

Files changed:
- cluster/distributed_coordinator.py (lines 302-314, 388-414)

cluster/distributed_coordinator.py

@@ -303,13 +303,16 @@ class DistributedCoordinator:
         """Execute command on worker via SSH"""
         worker = WORKERS[worker_id]
         
+        # CRITICAL FIX (Dec 1, 2025): Add SSH options to prevent prompts and improve reliability
+        ssh_opts = "-o StrictHostKeyChecking=no -o ConnectTimeout=10 -o ServerAliveInterval=5"
+        
         if 'ssh_hop' in worker:
             # Worker 2 requires hop through worker 1
             # CRITICAL FIX (Nov 29, 2025): Use double-nested quotes for 2-hop SSH
             # Single quotes don't pass command to inner SSH properly
-            ssh_cmd = f"ssh {worker['ssh_hop']} \"ssh {worker['host']} '{command}'\""
+            ssh_cmd = f"ssh {ssh_opts} {worker['ssh_hop']} \"ssh {ssh_opts} {worker['host']} '{command}'\""
         else:
-            ssh_cmd = f"ssh {worker['host']} '{command}'"
+            ssh_cmd = f"ssh {ssh_opts} {worker['host']} '{command}'"
         
         return subprocess.run(ssh_cmd, shell=True, capture_output=True, text=True)
     
@@ -381,21 +384,25 @@ class DistributedCoordinator:
         
         print(f"🚀 Starting chunk {chunk_id} on {worker_id} ({chunk_end - chunk_start:,} combos)...")
         
+        # CRITICAL FIX (Dec 1, 2025): Add SSH options for reliability and timeout handling
+        ssh_opts = "-o StrictHostKeyChecking=no -o ConnectTimeout=10 -o ServerAliveInterval=5"
+        
         # Execute command and capture result to verify it started
         if 'ssh_hop' in worker:
             # Worker 2 requires hop through worker 1
-            ssh_cmd = f"ssh {worker['ssh_hop']} \"ssh {worker['host']} '{cmd}' && echo 'Started chunk {chunk_id}' || echo 'FAILED'\""
+            ssh_cmd = f"ssh {ssh_opts} {worker['ssh_hop']} \"ssh {ssh_opts} {worker['host']} '{cmd}' && echo 'Started chunk {chunk_id}' || echo 'FAILED'\""
         else:
-            ssh_cmd = f"ssh {worker['host']} '{cmd}' && echo 'Started chunk {chunk_id}' || echo 'FAILED'"
+            ssh_cmd = f"ssh {ssh_opts} {worker['host']} '{cmd}' && echo 'Started chunk {chunk_id}' || echo 'FAILED'"
         
         # Use run() to capture output and verify success
+        # CRITICAL FIX (Dec 1, 2025): Increase timeout from 30s to 60s for nested SSH hops
         try:
             result = subprocess.run(
                 ssh_cmd,
                 shell=True,
                 capture_output=True,
                 text=True,
-                timeout=30  # 30 second timeout
+                timeout=60  # 60 second timeout (was 30s, too short for 2-hop SSH)
             )
             
             # Verify worker process started
@@ -409,6 +416,7 @@ class DistributedCoordinator:
                 return False
         except subprocess.TimeoutExpired:
             print(f"⚠️  SSH command timed out for {chunk_id} on {worker_id}")
+            print(f"   This usually means SSH hop is misconfigured or slow")
             return False
     
     def collect_results(self, worker_id: str, chunk_id: str) -> Optional[str]: