[client] bound system info / posture-check gathering with a timeout to prevent sync-loop freeze (#6512)

* Wraps syestem info / posture checks into a goroutine with timeout

e.checks = checks is set before doing the SyncMeta,
so if it fails next time isCheckEquals compares true and bypasses
the update. This is to avoid another repeating the 15 seconds hang.
The checks will be synced on reconnect or posture checks changes
push from mgmt.

* Propagate context to OS calls that can leverage its cancellation / timeout

* Distinguish timeout from cancellation in logs

* Dont log twice

* Block on timeout failure and reapply the exclude_ips

* Refactor for complexity

client/internal/engine.go

@@ -82,6 +82,12 @@ const (
 	PeerConnectionTimeoutMax = 45000 // ms
 	PeerConnectionTimeoutMin = 30000 // ms
 	disableAutoUpdate        = "disabled"
+
+	// systemInfoTimeout bounds how long the sync loop waits for system info / posture
+	// check gathering. The gathering runs uncancellable system calls (process scan,
+	// exec, os.Stat); without this bound a single stuck call freezes handleSync, and
+	// thus syncMsgMux, for as long as the call hangs (observed multi-minute freezes).
+	systemInfoTimeout = 15 * time.Second
 )
 
 var ErrResetConnection = fmt.Errorf("reset connection")
@@ -1084,11 +1090,22 @@ func (e *Engine) updateChecksIfNew(checks []*mgmProto.Checks) error {
 	}
 	e.checks = checks
 
-	info, err := system.GetInfoWithChecks(e.ctx, checks, e.overlayAddresses()...)
-	if err != nil {
-		log.Warnf("failed to get system info with checks: %v", err)
-		info = system.GetInfo(e.ctx)
+	info, ok := system.GetInfoWithChecksTimeout(e.ctx, systemInfoTimeout, checks, e.overlayAddresses()...)
+	if !ok {
+		// Gathering timed out; skip the meta sync this cycle rather than blocking the
+		// sync loop (and syncMsgMux) on a stuck system call. A later sync will retry.
+		return nil
 	}
+	e.applyInfoFlags(info)
+
+	if err := e.mgmClient.SyncMeta(info); err != nil {
+		return fmt.Errorf("could not sync meta: error %s", err)
+	}
+	return nil
+}
+
+// applyInfoFlags sets the engine's config-derived feature flags on the gathered system info.
+func (e *Engine) applyInfoFlags(info *system.Info) {
 	info.SetFlags(
 		e.config.RosenpassEnabled,
 		e.config.RosenpassPermissive,
@@ -1107,12 +1124,6 @@ func (e *Engine) updateChecksIfNew(checks []*mgmProto.Checks) error {
 		e.config.EnableSSHRemotePortForwarding,
 		e.config.DisableSSHAuth,
 	)
-
-	if err := e.mgmClient.SyncMeta(info); err != nil {
-		log.Errorf("could not sync meta: error %s", err)
-		return err
-	}
-	return nil
 }
 
 // overlayAddresses returns our own WireGuard overlay address (v4 and v6) so it
@@ -1272,31 +1283,15 @@ func (e *Engine) receiveManagementEvents() {
 	e.shutdownWg.Add(1)
 	go func() {
 		defer e.shutdownWg.Done()
-		info, err := system.GetInfoWithChecks(e.ctx, e.checks, e.overlayAddresses()...)
-		if err != nil {
-			log.Warnf("failed to get system info with checks: %v", err)
+		info, ok := system.GetInfoWithChecksTimeout(e.ctx, systemInfoTimeout, e.checks, e.overlayAddresses()...)
+		if !ok {
+			// Gathering timed out; connect the stream with base info so management
+			// connectivity still comes up rather than blocking here.
 			info = system.GetInfo(e.ctx)
 		}
-		info.SetFlags(
-			e.config.RosenpassEnabled,
-			e.config.RosenpassPermissive,
-			&e.config.ServerSSHAllowed,
-			e.config.DisableClientRoutes,
-			e.config.DisableServerRoutes,
-			e.config.DisableDNS,
-			e.config.DisableFirewall,
-			e.config.BlockLANAccess,
-			e.config.BlockInbound,
-			e.config.DisableIPv6,
-			e.config.LazyConnectionEnabled,
-			e.config.EnableSSHRoot,
-			e.config.EnableSSHSFTP,
-			e.config.EnableSSHLocalPortForwarding,
-			e.config.EnableSSHRemotePortForwarding,
-			e.config.DisableSSHAuth,
-		)
+		e.applyInfoFlags(info)
 
-		err = e.mgmClient.Sync(e.ctx, info, e.handleSync)
+		err := e.mgmClient.Sync(e.ctx, info, e.handleSync)
 		if err != nil {
 			// happens if management is unavailable for a long time.
 			// We want to cancel the operation of the whole client