fix(command): preserve fuse option after writers (#9972)

* fix(command): preserve fuse option after writers

Problem: FUSE mount option parsing skipped the option immediately following concurrentWriters, so values such as concurrentReaders could be silently ignored.

Root cause: runFuse incremented the options loop index inside the concurrentWriters case in addition to the loop increment.
Co-authored-by: Codex <noreply@openai.com>

* test: save and restore mountOptions pointers, not their values

The fields are reassigned to fresh heap variables during runFuse, so
dereferencing to back up/restore mutated throwaways instead of the
flag-bound originals and could nil-panic on unset fields.

---------

Co-authored-by: Codex <noreply@openai.com>
Co-authored-by: Chris Lu <chris.lu@gmail.com>

weed/command/fuse_std.go

@@ -165,7 +165,6 @@ func runFuse(cmd *Command, args []string) bool {
 				panic(fmt.Errorf("dirIdleEvictSec: %s", err))
 			}
 		case "concurrentWriters":
-			i++
 			if parsed, err := strconv.ParseInt(parameter.value, 0, 32); err == nil {
 				intValue := int(parsed)
 				mountOptions.concurrentWriters = &intValue

weed/command/fuse_std_test.go

@@ -0,0 +1,38 @@
+//go:build darwin || freebsd || linux
+
+package command
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+func TestRunFuseDoesNotSkipOptionAfterConcurrentWriters(t *testing.T) {
+	oldUmask := mountOptions.umaskString
+	oldWriters := mountOptions.concurrentWriters
+	oldReaders := mountOptions.concurrentReaders
+	oldFuseCommandPid := mountOptions.fuseCommandPid
+	oldDir := mountOptions.dir
+	defer func() {
+		mountOptions.umaskString = oldUmask
+		mountOptions.concurrentWriters = oldWriters
+		mountOptions.concurrentReaders = oldReaders
+		mountOptions.fuseCommandPid = oldFuseCommandPid
+		mountOptions.dir = oldDir
+
+		recovered := recover()
+		if recovered == nil {
+			t.Fatal("expected invalid concurrentReaders option to be parsed")
+		}
+		if !strings.Contains(fmt.Sprint(recovered), "concurrentReaders") {
+			t.Fatalf("expected concurrentReaders parse error, got %v", recovered)
+		}
+	}()
+
+	runFuse(cmdMount, []string{
+		"/mnt",
+		"-o",
+		"child=1,concurrentWriters=2,concurrentReaders=bad,umask=bad",
+	})
+}