Preparing for v2.0.0 branch merge

This commit reverts changes from v1.4.5 to v1.4.7, to prepare for v2.0.0
branch codes.

Changes includes in these releases have been included in v2.0.0 branch
already.

Details:

Revert "feat: add --rfc1918 flag for explicit LAN client support"

This reverts commit 0e3f764299.

Revert "Upgrade quic-go to v0.54.0"

This reverts commit e52402eb0c.

Revert "docs: add known issues documentation for Darwin 15.5 upgrade issue"

This reverts commit 2133f31854.

Revert "start mobile library with provision id and custom hostname."

This reverts commit a198a5cd65.

Revert "Add OPNsense new lease file"

This reverts commit 7af29cfbc0.

Revert ".github/workflows: bump go version to 1.24.x"

This reverts commit ce1a165348.

Revert "fix: ensure upstream health checks can handle large DNS responses"

This reverts commit fd48e6d795.

Revert "refactor(prog): move network monitoring outside listener loop"

This reverts commit d71d1341b6.

Revert "fix: correct Windows API constants to fix domain join detection"

This reverts commit 21855df4af.

Revert "refactor: move network monitoring to separate goroutine"

This reverts commit 66e2d3a40a.

Revert "refactor: extract empty string filtering to reusable function"

This reverts commit 36a7423634.

Revert "cmd/cli: ignore empty positional argument for start command"

This reverts commit e616091249.

Revert "Avoiding Windows runners file locking issue"

This reverts commit 0948161529.

Revert "refactor: split selfUpgradeCheck into version check and upgrade execution"

This reverts commit ce29b5d217.

Revert "internal/router: support Ubios 4.3+"

This reverts commit de24fa293e.

Revert "internal/router: support Merlin Guest Network Pro VLAN"

This reverts commit 6663925c4d.

cmd/cli/prog.go

@@ -35,7 +35,6 @@ import (
 	"github.com/Control-D-Inc/ctrld/internal/controld"
 	"github.com/Control-D-Inc/ctrld/internal/dnscache"
 	"github.com/Control-D-Inc/ctrld/internal/router"
-	"github.com/Control-D-Inc/ctrld/internal/router/dnsmasq"
 )
 
 const (
@@ -329,7 +328,7 @@ func (p *prog) apiConfigReload() {
 
 		// Performing self-upgrade check for production version.
 		if isStable {
-			_ = selfUpgradeCheck(resolverConfig.Ctrld.VersionTarget, curVer, &logger)
+			selfUpgradeCheck(resolverConfig.Ctrld.VersionTarget, curVer, &logger)
 		}
 
 		if resolverConfig.DeactivationPin != nil {
@@ -530,15 +529,6 @@ func (p *prog) run(reload bool, reloadCh chan struct{}) {
 		go p.watchLinkState(ctx)
 	}
 
-	if !reload {
-		go func() {
-			// Start network monitoring
-			if err := p.monitorNetworkChanges(); err != nil {
-				mainLog.Load().Error().Err(err).Msg("Failed to start network monitoring")
-			}
-		}()
-	}
-
 	for listenerNum := range p.cfg.Listener {
 		p.cfg.Listener[listenerNum].Init()
 		if !reload {
@@ -550,7 +540,7 @@ func (p *prog) run(reload bool, reloadCh chan struct{}) {
 				}
 				addr := net.JoinHostPort(listenerConfig.IP, strconv.Itoa(listenerConfig.Port))
 				mainLog.Load().Info().Msgf("starting DNS server on listener.%s: %s", listenerNum, addr)
-				if err := p.serveDNS(listenerNum); err != nil {
+				if err := p.serveDNS(ctx, listenerNum); err != nil {
 					mainLog.Load().Fatal().Err(err).Msgf("unable to start dns proxy on listener.%s", listenerNum)
 				}
 				mainLog.Load().Debug().Msgf("end of serveDNS listener.%s: %s", listenerNum, addr)
@@ -617,12 +607,6 @@ func (p *prog) setupClientInfoDiscover(selfIP string) {
 		format := ctrld.LeaseFileFormat(p.cfg.Service.DHCPLeaseFileFormat)
 		p.ciTable.AddLeaseFile(leaseFile, format)
 	}
-	if leaseFiles := dnsmasq.AdditionalLeaseFiles(); len(leaseFiles) > 0 {
-		mainLog.Load().Debug().Msgf("watching additional lease files: %v", leaseFiles)
-		for _, leaseFile := range leaseFiles {
-			p.ciTable.AddLeaseFile(leaseFile, ctrld.Dnsmasq)
-		}
-	}
 }
 
 // runClientInfoDiscover runs the client info discover.
@@ -1483,15 +1467,14 @@ func selfUninstallCheck(uninstallErr error, p *prog, logger zerolog.Logger) {
 	}
 }
 
-// shouldUpgrade checks if the version target vt is greater than the current one cv.
-// Major version upgrades are not allowed to prevent breaking changes.
+// selfUpgradeCheck checks if the version target vt is greater
+// than the current one cv, perform self-upgrade then.
 //
 // The callers must ensure curVer and logger are non-nil.
-// Returns true if upgrade is allowed, false otherwise.
-func shouldUpgrade(vt string, cv *semver.Version, logger *zerolog.Logger) bool {
+func selfUpgradeCheck(vt string, cv *semver.Version, logger *zerolog.Logger) {
 	if vt == "" {
 		logger.Debug().Msg("no version target set, skipped checking self-upgrade")
-		return false
+		return
 	}
 	vts := vt
 	if !strings.HasPrefix(vts, "v") {
@@ -1500,58 +1483,28 @@ func shouldUpgrade(vt string, cv *semver.Version, logger *zerolog.Logger) bool {
 	targetVer, err := semver.NewVersion(vts)
 	if err != nil {
 		logger.Warn().Err(err).Msgf("invalid target version, skipped self-upgrade: %s", vt)
-		return false
+		return
 	}
-
-	// Prevent major version upgrades to avoid breaking changes
-	if targetVer.Major() != cv.Major() {
-		logger.Warn().
-			Str("target", vt).
-			Str("current", cv.String()).
-			Msgf("major version upgrade not allowed (target: %d, current: %d), skipped self-upgrade", targetVer.Major(), cv.Major())
-		return false
-	}
-
 	if !targetVer.GreaterThan(cv) {
 		logger.Debug().
 			Str("target", vt).
 			Str("current", cv.String()).
 			Msgf("target version is not greater than current one, skipped self-upgrade")
-		return false
+		return
 	}
 
-	return true
-}
-
-// performUpgrade executes the self-upgrade command.
-// Returns true if upgrade was initiated successfully, false otherwise.
-func performUpgrade(vt string) bool {
 	exe, err := os.Executable()
 	if err != nil {
 		mainLog.Load().Error().Err(err).Msg("failed to get executable path, skipped self-upgrade")
-		return false
+		return
 	}
 	cmd := exec.Command(exe, "upgrade", "prod", "-vv")
 	cmd.SysProcAttr = sysProcAttrForDetachedChildProcess()
 	if err := cmd.Start(); err != nil {
 		mainLog.Load().Error().Err(err).Msg("failed to start self-upgrade")
-		return false
+		return
 	}
-	mainLog.Load().Debug().Msgf("self-upgrade triggered, version target: %s", vt)
-	return true
-}
-
-// selfUpgradeCheck checks if the version target vt is greater
-// than the current one cv, perform self-upgrade then.
-// Major version upgrades are not allowed to prevent breaking changes.
-//
-// The callers must ensure curVer and logger are non-nil.
-// Returns true if upgrade is allowed and should proceed, false otherwise.
-func selfUpgradeCheck(vt string, cv *semver.Version, logger *zerolog.Logger) bool {
-	if shouldUpgrade(vt, cv, logger) {
-		return performUpgrade(vt)
-	}
-	return false
+	mainLog.Load().Debug().Msgf("self-upgrade triggered, version target: %s", vts)
 }
 
 // leakOnUpstreamFailure reports whether ctrld should initiate a recovery flow