diff --git a/scripts/gen_full_supervisor.sh b/scripts/gen_full_supervisor.sh
new file mode 100755
index 0000000..2f0256f
--- /dev/null
+++ b/scripts/gen_full_supervisor.sh
@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+# Crash-resilient full-scale generation supervisor.
+#
+# gen_synthetic.py now (a) streams each sample to disk the instant it's produced
+# (O(workers) memory, not O(n)) and (b) supports --resume: it counts existing
+# lines and only generates+appends the missing suffix. So a kill mid-run keeps
+# all progress on disk; re-running --resume continues from where it stopped.
+#
+# This supervisor loops "run --resume -> check count" until the target line
+# count is reached. If the supervisor itself is killed, the data already on
+# disk survives; relaunch this script and it picks up. Convergence is guaranteed:
+# every iteration that survives adds >= 1 line.
+#
+# Usage: scripts/gen_full_supervisor.sh
+set -uo pipefail   # NB: no -e — a killed gen sub-call must NOT abort the loop
+cd "$(dirname "$0")/.."
+export PYTHONPATH=src
+W=$(nproc)
+
+gen() {  # target_n  out  seed  [extra flags...]
+  local target=$1 out=$2 seed=$3; shift 3
+  while :; do
+    local cur=0
+    if [ -f "$out" ]; then cur=$(wc -l < "$out"); fi
+    if [ "$cur" -ge "$target" ]; then
+      echo "[sup] $out done: $cur/$target lines"; return 0
+    fi
+    echo "[sup] $out at $cur/$target — launching --resume $(date '+%H:%M:%S')"
+    .venv/bin/python scripts/gen_synthetic.py \
+      --n "$target" --out "$out" --seed "$seed" --workers "$W" --resume "$@"
+    # loop: re-check count (gen may have been killed or completed)
+  done
+}
+
+echo "[sup] === START $(date '+%H:%M:%S') ==="
+gen 500000 data/align.jsonl 0
+gen 100000 data/sft.jsonl   0 --evolve
+echo "[sup] === ALL DONE $(date '+%H:%M:%S') ==="
+echo "[sup] align=$(wc -l < data/align.jsonl) sft=$(wc -l < data/sft.jsonl) eval=$(wc -l < data/eval_synth.jsonl)"
diff --git a/scripts/gen_synthetic.py b/scripts/gen_synthetic.py
index db8266d..a121b60 100644
--- a/scripts/gen_synthetic.py
+++ b/scripts/gen_synthetic.py
@@ -22,10 +22,11 @@ import json
 import os
 from concurrent.futures import ProcessPoolExecutor, as_completed
 from pathlib import Path
+from typing import Any
 
 from tqdm import tqdm
 
-from tsmm.data.gen_pipeline import gen_one_sample, write_jsonl
+from tsmm.data.gen_pipeline import _to_jsonable, gen_one_sample, write_jsonl
 from tsmm.data.instruct import evolve_instruction
 
 
@@ -55,19 +56,53 @@ def run(
     missing_rate: float = 0.05,
     event_prob: float = 0.5,
     do_evolve: bool = False,
+    resume: bool = False,
 ) -> int:
+    """Stream samples to ``out`` as they are produced.
+
+    Writes each sample to disk the instant its future completes, while keeping
+    the output file in index order via a tiny reorder buffer (size <= workers).
+    Peak memory is thus O(workers) instead of O(n): 500k samples never all sit
+    in RAM, and a crash loses only the unwritten tail rather than everything.
+
+    With ``resume=True`` (and ``--n`` as the *target* total), count existing
+    lines in ``out`` and only generate the missing suffix, appending. Repeated
+    crashes converge to the full target: each resume picks up where it stopped.
+    """
     Path(out).parent.mkdir(parents=True, exist_ok=True)
+    start_idx = 0
+    mode = "w"
+    if resume and os.path.exists(out):
+        with open(out, "r", encoding="utf-8") as f:
+            start_idx = sum(1 for _ in f)
+        if start_idx >= n:
+            print(f"[gen] {out} already has {start_idx} lines >= target {n}; nothing to do")
+            return start_idx
+        mode = "a"
+        print(f"[gen] resume: {out} has {start_idx}/{n}, appending {n - start_idx}")
     work = [
         (T, C, seed + i, anomaly_types, missing_rate, event_prob, do_evolve)
-        for i in range(n)
+        for i in range(start_idx, n)
     ]
-    samples = [None] * n
-    with ProcessPoolExecutor(max_workers=workers) as ex:
-        futures = {ex.submit(_one, w): i for i, w in enumerate(work)}
-        for fut in tqdm(as_completed(futures), total=n, desc=os.path.basename(out)):
+    written = start_idx
+    pending: dict[int, Any] = {}   # index -> sample, awaiting its turn
+    next_i = start_idx              # next index that must be flushed
+    with open(out, mode, encoding="utf-8") as f, \
+         ProcessPoolExecutor(max_workers=workers) as ex:
+        futures = {ex.submit(_one, w): i for i, w in zip(range(start_idx, n), work)}
+        for fut in tqdm(as_completed(futures), total=len(work),
+                        desc=os.path.basename(out), initial=start_idx):
             i = futures[fut]
-            samples[i] = fut.result()
-    return write_jsonl(samples, out)
+            pending[i] = fut.result()
+            # flush everything that is now contiguously ready, in order
+            while next_i in pending:
+                f.write(json.dumps(_to_jsonable(pending.pop(next_i)),
+                                   ensure_ascii=False))
+                f.write("\n")
+                next_i += 1
+                written += 1
+            f.flush()
+    return written
 
 
 def main(argv: list[str] | None = None) -> int:
@@ -81,6 +116,8 @@ def main(argv: list[str] | None = None) -> int:
     p.add_argument("--missing-rate", type=float, default=0.05)
     p.add_argument("--event-prob", type=float, default=0.5)
     p.add_argument("--evolve", action="store_true", help="apply Evol-Instruct rephrasing (for sft set)")
+    p.add_argument("--resume", action="store_true",
+                   help="count existing lines in --out and append only the missing suffix (crash-safe)")
     args = p.parse_args(argv)
 
     n = run(
@@ -93,6 +130,7 @@ def main(argv: list[str] | None = None) -> int:
         missing_rate=args.missing_rate,
         event_prob=args.event_prob,
         do_evolve=args.evolve,
+        resume=args.resume,
     )
     print(f"wrote {n} samples -> {args.out}")
     return 0