diff --git a/regress/cfg-client-free.sh b/regress/cfg-client-free.sh
new file mode 100644
index 000000000..9069163f6
--- /dev/null
+++ b/regress/cfg-client-free.sh
@@ -0,0 +1,51 @@
+#!/bin/sh
+
+# a client lost while the configuration is loading is freed
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+TMPDIR=$(mktemp -d) || exit 1
+TMUX="$TEST_TMUX -S$TMPDIR/tmux.sock"
+
+cleanup()
+{
+	touch $TMPDIR/go
+	$TMUX kill-server 2>/dev/null
+	rm -rf "$TMPDIR"
+}
+trap cleanup 0 1 15
+
+# Poll until a command succeeds.
+wait_for()
+{
+	i=0
+	while ! "$@"; do
+		[ $i -eq 100 ] && exit 1
+		i=$((i + 1))
+		sleep 0.1
+	done
+}
+
+# The run-shell holds the configuration until the go file exists.
+cat <<EOF >$TMPDIR/conf
+new-session -d -s keep
+run-shell 'touch $TMPDIR/started; i=0; while [ ! -f $TMPDIR/go ] && [ \$i -lt 100 ]; do sleep 0.1; i=\$((i + 1)); done'
+EOF
+
+cd $TMPDIR || exit 1
+$TMUX -v -f$TMPDIR/conf new-session -d -s first </dev/null &
+pid=$!
+wait_for test -f $TMPDIR/started
+kill $pid
+wait $pid
+log=$(echo $TMPDIR/tmux-server-*.log)
+wait_for grep -q 'lost client' $log
+c=$(sed -n 's/.* lost client //p' $log)
+
+# The client is freed straight away, well before the configuration ends.
+wait_for grep -q "free client $c " $log
+
+exit 0
diff --git a/regress/cfg-client-lost-before-wait.sh b/regress/cfg-client-lost-before-wait.sh
new file mode 100644
index 000000000..4402daf34
--- /dev/null
+++ b/regress/cfg-client-lost-before-wait.sh
@@ -0,0 +1,90 @@
+#!/bin/sh
+
+# A client lost before its configuration callback fires must not start waiting.
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+python3 - "$TEST_TMUX" "$(dirname "$0")/../tmux-protocol.h" <<'PY'
+import os
+from pathlib import Path
+import re
+import socket
+import struct
+import subprocess
+import sys
+import tempfile
+import time
+
+tmux = sys.argv[1]
+header = Path(sys.argv[2]).read_text()
+version = int(re.search(r"#define PROTOCOL_VERSION\s+(\d+)", header)[1])
+enum = re.search(r"enum msgtype\s*\{(.*?)\};", header, re.S)[1]
+enum = re.sub(r"/\*.*?\*/", "", enum, flags=re.S)
+types = {}
+value = 0
+for entry in enum.split(","):
+    entry = entry.strip()
+    if not entry:
+        continue
+    if "=" in entry:
+        entry, number = entry.split("=")
+        value = int(number.strip())
+    types[entry.strip()] = value
+    value += 1
+
+def message(name, body=b""):
+    return struct.pack("=IIII", types[name], 16 + len(body), version,
+        os.getpid()) + body
+
+def wait_for(predicate):
+    end = time.monotonic() + 5
+    while time.monotonic() < end:
+        result = predicate()
+        if result:
+            return result
+        time.sleep(0.05)
+    raise AssertionError("timed out waiting for client cleanup")
+
+with tempfile.TemporaryDirectory(prefix="tmux-cfg-early-") as tmp:
+    root = Path(tmp)
+    sockpath = root / "socket"
+    go = root / "go"
+    conf = root / "conf"
+    conf.write_text("run-shell 'i=0; while [ ! -f %s ] && [ $i -lt 100 ]; "
+        "do sleep 0.1; i=$((i + 1)); done'\n" % go)
+    server = subprocess.Popen([tmux, "-D", "-v", "-S", str(sockpath),
+        "-f", str(conf)], cwd=tmp, stdout=subprocess.DEVNULL)
+    logpath = root / ("tmux-server-%d.log" % server.pid)
+
+    def log():
+        return logpath.read_text() if logpath.exists() else ""
+
+    try:
+        wait_for(sockpath.exists)
+        with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as client:
+            client.connect(str(sockpath))
+            # Both messages are read together. The short MSG_COMMAND makes
+            # proc_event_cb lose the client before server_loop runs its queue.
+            client.sendall(message("MSG_IDENTIFY_CWD", tmp.encode() + b"\0") +
+                message("MSG_IDENTIFY_CLIENTPID", struct.pack("=i", os.getpid())) +
+                message("MSG_IDENTIFY_DONE") + message("MSG_COMMAND"))
+            lost = wait_for(lambda: re.search(r"lost client (\S+)", log()))[1]
+            wait_for(lambda: "free client %s (0 references)" % lost in log())
+            contents = log()
+            callback = "cmdq_next <client-%d>: [cfg_client_done/" % os.getpid()
+            assert contents.index("lost client " + lost) < \
+                contents.index(callback), contents
+            # Cleanup must happen while configuration is still blocked.
+            assert "cmdq_next <global>: [cfg_done/" not in contents, contents
+    finally:
+        go.touch()
+        server.terminate()
+        try:
+            server.wait(timeout=3)
+        except subprocess.TimeoutExpired:
+            server.kill()
+            server.wait()
+PY
diff --git a/regress/cfg-load-once.sh b/regress/cfg-load-once.sh
new file mode 100644
index 000000000..b9f4289e1
--- /dev/null
+++ b/regress/cfg-load-once.sh
@@ -0,0 +1,60 @@
+#!/bin/sh
+
+# the configuration is loaded once if the client that started it is lost, and
+# the next client still waits for it to finish
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+TMPDIR=$(mktemp -d) || exit 1
+TMUX="$TEST_TMUX -S$TMPDIR/tmux.sock"
+
+cleanup()
+{
+	touch $TMPDIR/go
+	$TMUX kill-server 2>/dev/null
+	rm -rf "$TMPDIR"
+}
+trap cleanup 0 1 15
+
+# Poll until a command succeeds.
+wait_for()
+{
+	i=0
+	while ! "$@"; do
+		[ $i -eq 100 ] && exit 1
+		i=$((i + 1))
+		sleep 0.1
+	done
+}
+
+# The run-shell holds the configuration until the go file exists.
+cat <<EOF >$TMPDIR/conf
+set -ga @runs x
+new-session -d -s keep
+run-shell 'touch $TMPDIR/started; i=0; while [ ! -f $TMPDIR/go ] && [ \$i -lt 100 ]; do sleep 0.1; i=\$((i + 1)); done'
+set -g @late 1
+EOF
+
+cd $TMPDIR || exit 1
+$TMUX -v -f$TMPDIR/conf new-session -d -s first </dev/null &
+pid=$!
+wait_for test -f $TMPDIR/started
+kill $pid
+wait $pid
+log=$(echo $TMPDIR/tmux-server-*.log)
+wait_for grep -q 'lost client' $log
+
+# The second client must identify before the configuration is released.
+$TMUX new-session -d -s second \; display -p '#{@runs} #{@late}' \
+	</dev/null >$TMPDIR/out &
+pid=$!
+wait_for grep -q "name is client-$pid\$" $log
+touch $TMPDIR/go
+wait $pid || exit 1
+
+[ "$(cat $TMPDIR/out)" = "x 1" ] || exit 1
+
+exit 0
diff --git a/regress/swap-pane-zoom-error.sh b/regress/swap-pane-zoom-error.sh
new file mode 100644
index 000000000..0d85f72f1
--- /dev/null
+++ b/regress/swap-pane-zoom-error.sh
@@ -0,0 +1,40 @@
+#!/bin/sh
+
+# swap-pane refusing a floating pane must leave the zoom alone
+
+PATH=/bin:/usr/bin
+TERM=screen
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+$TMUX kill-server 2>/dev/null
+
+TMP=$(mktemp)
+trap "rm -f $TMP; $TMUX kill-server 2>/dev/null" 0 1 15
+
+$TMUX new -d
+$TMUX splitw -d
+$TMUX new-pane -d
+
+echo $($TMUX lsp -F'#{pane_id}:#{pane_floating_flag}') >$TMP
+(echo "%0:0 %1:0 %2:1"|cmp -s - $TMP) || exit 1
+
+$TMUX resize-pane -Z -t %0
+[ "$($TMUX display -p '#{window_zoomed_flag}')" = 1 ] || exit 1
+
+$TMUX swap-pane -Z -D -t %2
+[ "$?" = 0 ] && exit 1
+[ "$($TMUX display -p '#{window_zoomed_flag}')" = 1 ] || exit 1
+
+$TMUX swap-pane -Z -U -t %2
+[ "$?" = 0 ] && exit 1
+[ "$($TMUX display -p '#{window_zoomed_flag}')" = 1 ] || exit 1
+
+# A swap that is allowed still happens.
+$TMUX swap-pane -D -t %0 || exit 1
+echo $($TMUX lsp -F'#{pane_id}') >$TMP
+(echo "%1 %0 %2"|cmp -s - $TMP) || exit 1
+
+$TMUX kill-server 2>/dev/null
+
+exit 0