fix: close leaked fds in openpty fallback, add static assertions

atch.h

@@ -115,6 +115,8 @@ struct packet
 		struct winsize ws;
 	} u;
 };
+_Static_assert(sizeof(((struct packet *)0)->u.buf) <= 255,
+	"packet buffer must fit in uint8_t length");
 
 /*
 ** The master sends a simple stream of text to the attaching clients, without

config.h

@@ -22,6 +22,8 @@
 #ifndef SCROLLBACK_SIZE
 #define SCROLLBACK_SIZE (128 * 1024)
 #endif
+_Static_assert(SCROLLBACK_SIZE > 0 && (SCROLLBACK_SIZE & (SCROLLBACK_SIZE - 1)) == 0,
+	"SCROLLBACK_SIZE must be a positive power of two");
 
 /* Maximum size of the on-disk session log; older bytes are trimmed on open */
 #ifndef LOG_MAX_SIZE

master.c

@@ -802,29 +802,29 @@ int
 openpty(int *amaster, int *aslave, char *name, struct termios *termp,
 	struct winsize *winp)
 {
-	int master, slave;
+	int master = -1, slave = -1;
 	char *buf;
 
 	master = open("/dev/ptmx", O_RDWR);
 	if (master < 0)
 		return -1;
 	if (grantpt(master) < 0)
-		return -1;
+		goto fail;
 	if (unlockpt(master) < 0)
-		return -1;
+		goto fail;
 	buf = ptsname(master);
 	if (!buf)
-		return -1;
+		goto fail;
 
 	slave = open(buf, O_RDWR | O_NOCTTY);
 	if (slave < 0)
-		return -1;
+		goto fail;
 
 #ifdef I_PUSH
 	if (ioctl(slave, I_PUSH, "ptem") < 0)
-		return -1;
+		goto fail;
 	if (ioctl(slave, I_PUSH, "ldterm") < 0)
-		return -1;
+		goto fail;
 #endif
 
 	*amaster = master;
@@ -836,6 +836,13 @@ openpty(int *amaster, int *aslave, char *name, struct termios *termp,
 	if (winp)
 		ioctl(slave, TIOCSWINSZ, winp);
 	return 0;
+
+fail:
+	if (master >= 0)
+		close(master);
+	if (slave >= 0)
+		close(slave);
+	return -1;
 }
 
 pid_t

tests/test.sh

@@ -720,6 +720,34 @@ assert_contains "no args: shows Usage:"              "Usage:" "$out"
 run "$ATCH" --help
 assert_contains "help: shows tail command"           "tail" "$out"
 
+# ── 23. fd leak: rapid session cycling under low fd limit ──────────────────
+# openpty fallback leaks fds on error paths. Under a tight fd limit,
+# leaked fds accumulate and eventually prevent new sessions from starting.
+
+(
+    ulimit -n 64 2>/dev/null || true
+    LEAK_FAIL=0
+    i=0
+    while [ $i -lt 50 ]; do
+        out=$("$ATCH" start "leak-$i" sleep 999 2>&1)
+        lrc=$?
+        if [ "$lrc" -ne 0 ]; then
+            LEAK_FAIL=1
+            break
+        fi
+        "$ATCH" kill "leak-$i" >/dev/null 2>&1
+        sleep 0.02
+        i=$((i + 1))
+    done
+    i=0; while [ $i -lt 50 ]; do "$ATCH" kill "leak-$i" >/dev/null 2>&1; i=$((i + 1)); done
+    exit $LEAK_FAIL
+)
+if [ $? -eq 0 ]; then
+    ok "fd-leak: 50 create/destroy cycles under ulimit -n 64"
+else
+    fail "fd-leak: session failed under low fd limit (possible fd leak)" "50 cycles" "failed early"
+fi
+
 # ── summary ──────────────────────────────────────────────────────────────────
 
 printf "\n1..%d\n" "$T"