u/cascade: validate -max-workers; truncate large worker outputs

- Reject non-positive-integer -max-workers early
- Per-worker output capped at OLLIE_CASCADE_MAX_OUTPUT (default 8000 chars)
  to prevent synthesis prompt blowup

scripts/u/cascade

@@ -56,6 +56,10 @@ else
 fi
 [ -z "$task" ] && die "empty prompt"
 
+case "$max_workers" in
+    ''|*[!0-9]*|0) die "-max-workers must be a positive integer" ;;
+esac
+
 # Step 1: Ask the planner to decompose into subtasks (JSON array).
 plan=$("$B" -backend "$PB" -model "$PM" -json \
     "Decompose this task into independent, mechanical subtasks that a weak model can execute without judgment. Each subtask must be fully self-contained (include all needed context). Output a JSON array of objects with \"id\" (short string) and \"instruction\" (complete task description). Keep it minimal — only decompose what benefits from parallelism.
@@ -100,6 +104,7 @@ done
 for pid in "${pids[@]}"; do wait "$pid" || true; done
 
 # Step 4: Gather results as structured JSON array.
+MAX_OUTPUT=${OLLIE_CASCADE_MAX_OUTPUT:-8000}  # max chars per worker output
 failures=0
 results_json="["
 first=1
@@ -111,6 +116,10 @@ for sid in "${workers[@]}"; do
         failures=$((failures + 1))
     fi
     out=$(cat "${tmpdir}/${sid}.out" 2>/dev/null || echo "(no output)")
+    if [ "${#out}" -gt "$MAX_OUTPUT" ]; then
+        out="${out:0:$MAX_OUTPUT}
+...(truncated, ${#out} chars total)"
+    fi
     [ "$first" -eq 1 ] && first=0 || results_json="${results_json},"
     results_json="${results_json}$(jq -n --arg id "$sid" --arg status "$status" --arg output "$out" \
         '{id: $id, status: $status, output: $output}')"