fix(chat): GLM review batch — corruption, traversal, cursor truncation, double print (v4.6.78-80)

12 findings accepted, 3 refuted with evidence (see _docs/chat-review-glm-2026-10-23.md).

Data loss: a corrupt thread read as [] and the next append rewrote it with one message —
now 500 and the file is left alone. Cursor after a >50-message truncation pointed at the
thread tail, making the oldest permanently unfetchable — now the last message actually
sent, plus truncated:true. Two posts in the same millisecond shared a cursor — epoch is
now strictly increasing.

Security: chat.py show() had no id validation and joined argv onto CHAT_DIR ('../../x'
read any .json as darkbot) — THREAD_RE added. The auto-reply prompt now treats message
text as untrusted data and forbids acting on instructions found in it.

Ops: relay housekeeping swept neither .lock-* nor orphaned .tmp-*; a crashed listing
looked identical to an empty queue; grep AWAITING also matched message bodies; hermes-poll
printed every reply twice.

Verified: corrupt file -> 500 with the file untouched; traversal -> 'invalid thread id';
hermes-poll -> exactly one line per reply.

1 files changed, 33 insertions, 6 deletions

diff --git a/scripts/chat.py b/scripts/chat.py
index 5b44b64..821bb31 100755
--- a/scripts/chat.py
+++ b/scripts/chat.py
@@ -24,11 +24,22 @@ def now_ms():
 
 
 def load(path):
-    try:
-        with open(path) as f:
-            return json.load(f)
-    except Exception:
+    """Read a thread. Missing is empty; corrupt is an error.
+
+    Returning [] for both let reply() rewrite a damaged thread with a single message —
+    history gone, and nothing said so.
+    """
+    if not os.path.exists(path):
         return []
+    with open(path) as f:
+        raw = f.read()
+    try:
+        data = json.loads(raw)
+    except json.JSONDecodeError as exc:
+        raise SystemExit('thread file is corrupt (%s): %s' % (path, exc))
+    if not isinstance(data, list):
+        raise SystemExit('thread file is not a list: ' + path)
+    return data
 
 
 def threads():
@@ -38,7 +49,14 @@ def threads():
     for name in sorted(os.listdir(CHAT_DIR)):
         if not name.endswith('.json') or name.startswith('.'):
             continue
-        msgs = load(os.path.join(CHAT_DIR, name))
+        try:
+            msgs = load(os.path.join(CHAT_DIR, name))
+        except SystemExit as exc:
+            # one unreadable file must not make the whole listing fail: that is how
+            # awaiting messages silently stop being listed
+            out.append({'thread': name[:-5], 'count': -1, 'last_ts': '', 'last_author': 'corrupt',
+                        'awaiting': True, 'preview': 'CORRUPT: ' + str(exc)[:90]})
+            continue
         if not msgs:
             continue
         last = msgs[-1]
@@ -62,6 +80,10 @@ def reply(thread, text):
         raise SystemExit('no such thread: ' + thread)
     lockpath = os.path.join(CHAT_DIR, '.lock-' + thread)
     with open(lockpath, 'a+') as lock:
+        # created here as darkbot (0644 under umask 022); PHP opens the same lock as
+        # www-data, so group write is mandatory or later posts to this thread 500
+        try: os.chmod(lockpath, 0o664)
+        except OSError: pass
         fcntl.flock(lock, fcntl.LOCK_EX)
         try:
             msgs = load(path)
@@ -102,10 +124,15 @@ def main():
             return 0
         for t in rows:
             flag = 'AWAITING' if t['awaiting'] else 'replied '
-            print(f"{t['thread']}  {flag}  {t['count']:>3} msg  {t['last_ts']}  {t['preview']}")
+            if t['count'] == -1:
+                flag = 'CORRUPT '
+            print(f"{t['thread']}  {flag}  {max(t['count'], 0):>3} msg  {t['last_ts']}  {t['preview']}")
         return 0
 
     if cmd == 'show' and len(sys.argv) >= 3:
+        # reply() validated the id, show() did not: '../../x' joined straight onto CHAT_DIR
+        if not THREAD_RE.match(sys.argv[2]):
+            raise SystemExit('invalid thread id (expected 16 lowercase hex chars)')
         msgs = load(os.path.join(CHAT_DIR, sys.argv[2] + '.json'))
         if not msgs:
             print('(empty or unknown thread)')