refactor(controller): apply controller settings by rebuilding the channel set

Giving each controller a Reload method worked for the notification pipes, which
only hold values, but not for the two bot channels: the NapCat client is stopped
through a sync.Once and the Telegram polling context is created with the
controller, so neither can be re-pointed once running. It also meant five
bespoke implementations of the same idea.

Replace the whole set instead. Manager.ReplaceAll swaps in a freshly built set
under the registry lock, stops the outgoing controllers outside it, and starts
the incoming ones off the calling goroutine so a slow handshake does not hold
the settings request open. ReplaceAll is now the only way controllers are
installed: Register is gone, because a lone registration would slip a controller
in without recording the settings it was built from, which is what NeedsRebuild
compares against.

The rebuild runs from the reload hook and only fires when the controllerMethod
section actually changed, so saving a message template or a webhook endpoint
leaves the channels alone. NeedsRebuild compares the whole section by value, and
a test pins that reloading a file reproduces it exactly — a default applied
inconsistently would make every save look like a controller change and tear down
every channel.

With controllers immutable after construction and replaced wholesale, the atomic
pointers and Reload methods have no writers left, so they are gone and the pipes
return to plain fields. notifyReload now serializes hook execution for the same
reason: a hook mutates process-wide state, and two overlapping settings updates
would otherwise each decide to rebuild from their own view of what was applied.

Kept from that work: applyEmailProxy restores gomail's default dialer when
networkUseProxy is turned off. The old constructor only ever installed the proxy
dialer, so switching the flag back left SMTP tunnelled through a proxy with no
way to undo it short of a restart.

Documents the resulting behaviour in the README under "What applies without a
restart".

internal/controller/pipes/email.go

@@ -3,8 +3,6 @@ package pipes
 import (
 	"fmt"
 	"net"
-	"reflect"
-	"sync/atomic"
 
 	gomail "gopkg.in/mail.v2"
 
@@ -18,26 +16,17 @@ import (
 
 // EmailController handles email notifications via SMTP.
 //
-// The configuration is held behind an atomic pointer rather than in a plain
-// field: Reload replaces it on the settings-update goroutine while the send
-// methods read it on the status-change and incoming-webhook goroutines.
+// cfg is written once, by the constructor, and never again: a controller that
+// needs different settings is replaced wholesale by the manager rather than
+// reconfigured in place, so the send methods can read it without locking.
 type EmailController struct {
-	cfg atomic.Pointer[config.EmailConfig]
+	cfg config.EmailConfig
 }
 
 // NewEmailController creates a new Email controller.
 func NewEmailController(cfg config.EmailConfig) *EmailController {
-	e := &EmailController{}
-	e.cfg.Store(&cfg)
 	applyEmailProxy(cfg.NetworkUseProxy)
-	return e
-}
-
-// settings returns the configuration currently in effect. The value it points
-// at is never mutated after being stored, so a caller can hold the pointer for
-// one whole send without a concurrent Reload disturbing it.
-func (e *EmailController) settings() *config.EmailConfig {
-	return e.cfg.Load()
+	return &EmailController{cfg: cfg}
 }
 
 // applyEmailProxy routes SMTP through the HTTP CONNECT proxy, or restores a
@@ -61,7 +50,7 @@ func (e *EmailController) Name() string {
 
 // Start initializes the Email controller.
 func (e *EmailController) Start() error {
-	if !e.settings().Enabled {
+	if !e.cfg.Enabled {
 		postLog.Info("Email controller is disabled")
 		return nil
 	}
@@ -74,121 +63,90 @@ func (e *EmailController) Stop() {
 	postLog.Info("Email controller stopped")
 }
 
-// Reload applies the current configuration. Swapping in the new settings is
-// enough for everything read at the point of use; the proxy setting is the
-// exception, because it is baked into gomail's package-level dialer when the
-// controller is built rather than consulted per send.
-func (e *EmailController) Reload() {
-	global := config.Current()
-	if global == nil {
-		return
-	}
-
-	current := e.settings()
-	updated := global.ControllerMethod.Email
-	// EmailConfig carries a recipient slice, so it is not comparable with ==.
-	if reflect.DeepEqual(*current, updated) {
-		return
-	}
-
-	if current.NetworkUseProxy != updated.NetworkUseProxy {
-		applyEmailProxy(updated.NetworkUseProxy)
-	}
-	e.cfg.Store(&updated)
-	postLog.Debug("Email controller reloaded")
-}
-
 // IsEnabled returns whether the controller is enabled.
 func (e *EmailController) IsEnabled() bool {
-	return e.settings().Enabled
+	return e.cfg.Enabled
 }
 
 // IsMarkdown returns whether the channel renders Markdown, per its markdown
 // setting in config.json.
 func (e *EmailController) IsMarkdown() bool {
-	return e.settings().Markdown
+	return e.cfg.Markdown
 }
 
 // SendStatusChange sends a status change notification via Email.
 func (e *EmailController) SendStatusChange(change node.StatusChange) error {
-	s := e.settings()
-	if !s.Enabled {
+	if !e.cfg.Enabled {
 		return nil
 	}
-	if len(s.To) == 0 {
+	if len(e.cfg.To) == 0 {
 		postLog.Debug("Email controller has no recipients configured")
 		return nil
 	}
 
 	cfg := config.Current()
 	params := template.BuildParamsFromStatusChange(change)
-	body := template.Render(cfg.ControllerMessage.ServerStatusChanged, params, s.Markdown)
+	body := template.Render(cfg.ControllerMessage.ServerStatusChanged, params, e.cfg.Markdown)
 
 	subject := fmt.Sprintf("Server Status Change: %s - %s", change.Name, change.Event)
-	return e.sendEmail(s, subject, body)
+	return e.sendEmail(subject, body)
 }
 
 // SendServerList sends the server list via Email.
 func (e *EmailController) SendServerList(onlineServers, offlineServers string) error {
-	s := e.settings()
-	if !s.Enabled || len(s.To) == 0 {
+	if !e.cfg.Enabled || len(e.cfg.To) == 0 {
 		return nil
 	}
 
 	cfg := config.Current()
 	params := template.BuildParamsFromServerList()
-	body := template.Render(cfg.ControllerMessage.ServerList, params, s.Markdown)
+	body := template.Render(cfg.ControllerMessage.ServerList, params, e.cfg.Markdown)
 
-	return e.sendEmail(s, "Server List", body)
+	return e.sendEmail("Server List", body)
 }
 
 // SendExecuteResult sends a command execution result via Email.
 func (e *EmailController) SendExecuteResult(serverName, serverUUID, command, result string) error {
-	s := e.settings()
-	if !s.Enabled || len(s.To) == 0 {
+	if !e.cfg.Enabled || len(e.cfg.To) == 0 {
 		return nil
 	}
 
 	cfg := config.Current()
 	params := template.BuildParamsFromExecResult(serverName, serverUUID, command, result)
-	body := template.Render(cfg.ControllerMessage.ServerExecuteResult, params, s.Markdown)
+	body := template.Render(cfg.ControllerMessage.ServerExecuteResult, params, e.cfg.Markdown)
 
 	subject := fmt.Sprintf("Command Result: %s on %s", command, serverName)
-	return e.sendEmail(s, subject, body)
+	return e.sendEmail(subject, body)
 }
 
 // SendAlert sends an alert submitted through the incoming webhook API to the
 // configured recipients.
 func (e *EmailController) SendAlert(alert controller.Alert) error {
-	s := e.settings()
-	if !s.Enabled {
+	if !e.cfg.Enabled {
 		return nil
 	}
-	if len(s.To) == 0 {
+	if len(e.cfg.To) == 0 {
 		postLog.Debug("Email controller has no recipients configured")
 		return nil
 	}
 
-	return e.sendEmail(s, alert.Subject, alert.Render(s.Markdown))
+	return e.sendEmail(alert.Subject, alert.Render(e.cfg.Markdown))
 }
 
-// sendEmail delivers one message using the settings the caller already
-// snapshotted, so the recipients the guard approved are the recipients that
-// receive it even if a reload lands mid-send.
-func (e *EmailController) sendEmail(s *config.EmailConfig, subject, body string) error {
+func (e *EmailController) sendEmail(subject, body string) error {
 	m := gomail.NewMessage()
-	m.SetHeader("From", s.From)
-	m.SetHeader("To", s.To...)
+	m.SetHeader("From", e.cfg.From)
+	m.SetHeader("To", e.cfg.To...)
 	m.SetHeader("Subject", subject)
 	m.SetBody("text/plain", body)
 
-	d := gomail.NewDialer(s.SMTPHost, s.SMTPPort, s.Username, s.Password)
+	d := gomail.NewDialer(e.cfg.SMTPHost, e.cfg.SMTPPort, e.cfg.Username, e.cfg.Password)
 
 	if err := d.DialAndSend(m); err != nil {
 		postLog.Warning("Failed to send email: " + err.Error())
 		return err
 	}
 
-	postLog.Debug("Email sent successfully to " + fmt.Sprintf("%v", s.To))
+	postLog.Debug("Email sent successfully to " + fmt.Sprintf("%v", e.cfg.To))
 	return nil
 }