From ed8cac4ac29250ae8c34c82452a5e02425a8e3ba Mon Sep 17 00:00:00 2001
From: Bernhard Guillon <Bernhard.Guillon@begu.org>
Date: Tue, 7 Jul 2026 18:54:02 +0200
Subject: Add sync_done handshake: server signals when ready, client waits
 before watching

---
 cmd_linux.go   |  4 ++++
 cmd_windows.go | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/cmd_linux.go b/cmd_linux.go
index 4239d1d..d9d392e 100644
--- a/cmd_linux.go
+++ b/cmd_linux.go
@@ -126,6 +126,10 @@ func handleClient(conn net.Conn, stack *GitignoreStack) {
 			logInfo("sync: done")
 			logInfo("watcher: monitoring for changes ...")
 			conn.SetReadDeadline(time.Time{}) // no timeout during event monitoring
+			doneMsg := &ProtocolMessage{Type: "sync_done"}
+			doneData, _ := EncodeMessage(doneMsg)
+			doneData = append(doneData, '\n')
+			conn.Write(doneData)
 
 		case "event_create":
 			logDebug("event: create %s", msg.Path)
diff --git a/cmd_windows.go b/cmd_windows.go
index f728182..f722b47 100644
--- a/cmd_windows.go
+++ b/cmd_windows.go
@@ -3,6 +3,7 @@
 package main
 
 import (
+	"bufio"
 	"context"
 	"flag"
 	"fmt"
@@ -92,6 +93,14 @@ func run() {
 			continue
 		}
 
+		logInfo("watcher: waiting for server to finish sync ...")
+
+		if err := waitForSyncDone(conn); err != nil {
+			logErrorf("wait for sync_done: %v", err)
+			conn.Close()
+			continue
+		}
+
 		logInfo("watcher: monitoring for changes ...")
 
 		// Heartbeat goroutine to detect disconnects
@@ -387,6 +396,30 @@ func sendEvent(conn net.Conn, evt FileEvent) error {
 	return err
 }
 
+func waitForSyncDone(conn net.Conn) error {
+	scanner := bufio.NewScanner(conn)
+	scanner.Buffer(make([]byte, 0, 1024*1024), 1024*1024)
+	conn.SetReadDeadline(time.Now().Add(10 * time.Minute)) // large repos can take a while
+	defer conn.SetReadDeadline(time.Time{})
+	for scanner.Scan() {
+		msg, err := DecodeMessage(scanner.Bytes())
+		if err != nil {
+			continue
+		}
+		switch msg.Type {
+		case "sync_done":
+			return nil
+		case "ping":
+			// respond to heartbeats during long sync
+			pong := &ProtocolMessage{Type: "pong"}
+			data, _ := EncodeMessage(pong)
+			data = append(data, '\n')
+			conn.Write(data)
+		}
+	}
+	return fmt.Errorf("connection closed before sync_done")
+}
+
 func addWatchersRecursively(watcher *fsnotify.Watcher, root string, stack *GitignoreStack) error {
 	var count, failCount, skippedCount int
 	bufBytes := *bufSizeKB * 1024
-- 
cgit v1.2.3