fix(kugetsu): improve session detection in cmd_start with retry logic and logging

- Capture fork output to log file for debugging
- Track fork PID to detect if process exits early
- Retry session detection up to 10 seconds instead of 1 second
- Show fork log output when session creation fails
- Improve error message to indicate timeout

skills/kugetsu/scripts/kugetsu

@@ -1237,24 +1237,35 @@ cmd_start() {
         exit 1
     fi
     
+    local fork_log="$SESSIONS_DIR/$session_file.fork.log"
+    
     if [ "$DEBUG_MODE" = true ]; then
-        opencode run "$message" --fork --session "$base_session_id" --dir "$worktree_path" 2>&1 | tee "$SESSIONS_DIR/$session_file.debug.log" &
+        opencode run "$message" --fork --session "$base_session_id" --dir "$worktree_path" 2>&1 | tee "$fork_log" &
     else
-        opencode run "$message" --fork --session "$base_session_id" --dir "$worktree_path" 2>&1 &
+        opencode run "$message" --fork --session "$base_session_id" --dir "$worktree_path" >> "$fork_log" 2>&1 &
     fi
 
-    # Wait briefly for session to be created
+    local fork_pid=$!
+    
+    local max_attempts=10
+    local attempt=1
+    local new_session_id=""
+    
+    while [ $attempt -le $max_attempts ]; do
         sleep 1
         
-    # Find the new session by comparing before/after lists
-    # Skip any session that existed before the fork and skip base/pm-agent
-    local new_session_id=""
+        if ! kill -0 $fork_pid 2>/dev/null; then
+            if [ -s "$fork_log" ]; then
+                echo "Fork command exited. Log output:" >&2
+                tail -20 "$fork_log" >&2
+            fi
+            break
+        fi
+        
         while IFS= read -r sess; do
-        # Skip base and pm-agent
             [ "$sess" = "$base_session_id" ] && continue
             [ "$sess" = "$pm_agent_session_id" ] && continue
             
-        # Check if this session existed before
             local existed_before=false
             for before_sess in "${before_sessions[@]}"; do
                 if [ "$sess" = "$before_sess" ]; then
@@ -1269,8 +1280,19 @@ cmd_start() {
             fi
         done < <(opencode session list 2>/dev/null | grep -oP '^ses_\w+')
         
+        if [ -n "$new_session_id" ]; then
+            break
+        fi
+        
+        attempt=$((attempt + 1))
+    done
+
     if [ -z "$new_session_id" ]; then
-        echo "Error: Could not find newly created session" >&2
+        echo "Error: Could not find newly created session after ${max_attempts}s" >&2
+        if [ -f "$fork_log" ] && [ -s "$fork_log" ]; then
+            echo "Fork log:" >&2
+            tail -30 "$fork_log" >&2
+        fi
         remove_worktree_for_issue "$issue_ref"
         exit 1
     fi