refactor(kernel)!: feature providers are opt-in packages, not kernel defaults

Only 'log' is a core default. cache/queue/storage/realtime/i18n move to
togo/providers/* and self-register when blank-imported. A project enables
features by importing the packages (chosen at `togo new`); the kernel core
hard-codes no features.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: fadymondy

provider.go

@@ -1,21 +1,13 @@
 package togo
 
-import (
-	"sort"
-
-	"github.com/togo-framework/togo/cache"
-	"github.com/togo-framework/togo/i18n"
-	"github.com/togo-framework/togo/queue"
-	"github.com/togo-framework/togo/realtime"
-	"github.com/togo-framework/togo/storage"
-)
+import "sort"
 
 // Provider contributes a service to the kernel. The kernel core is tiny (config,
-// router, hooks, plugin lifecycle); EVERY other capability — including the
-// built-in log/cache/queue/storage/realtime/i18n — is registered as a Provider.
-// Nothing is hard-coded in the core: providers run in ascending Priority, and a
-// later provider for the same capability overrides an earlier one, so any plugin
-// can inject or replace anything by calling RegisterProvider in its init().
+// router, hooks, log, plugin lifecycle). Every OTHER capability — cache, queue,
+// storage, realtime, i18n, db drivers — lives in its own provider package under
+// togo/providers/* and self-registers in init(). A project opts into features by
+// blank-importing those packages (chosen at `togo new`), so the core hard-codes
+// nothing and any plugin can inject/override a provider globally.
 type Provider interface {
 	ProviderName() string
 	ProviderPriority() int
@@ -25,49 +17,37 @@ type Provider interface {
 // providerRegistry is the global, append-only provider list (defaults + plugins).
 var providerRegistry []Provider
 
-// RegisterProvider registers a service provider globally. Call it from a
-// package init() (the built-in defaults do exactly this). Higher Priority runs
-// later and wins.
+// RegisterProvider registers a service provider globally (call from init()).
+// Higher Priority runs later and wins.
 func RegisterProvider(p Provider) { providerRegistry = append(providerRegistry, p) }
 
-// providerFunc adapts a func to a Provider.
 type providerFunc struct {
 	name     string
 	priority int
 	fn       func(*Kernel) error
 }
 
-func (p providerFunc) ProviderName() string   { return p.name }
-func (p providerFunc) ProviderPriority() int  { return p.priority }
+func (p providerFunc) ProviderName() string    { return p.name }
+func (p providerFunc) ProviderPriority() int   { return p.priority }
 func (p providerFunc) Provide(k *Kernel) error { return p.fn(k) }
 
-// RegisterProviderFunc is a convenience for registering a provider from a func.
+// RegisterProviderFunc registers a provider from a func.
 func RegisterProviderFunc(name string, priority int, fn func(*Kernel) error) {
 	RegisterProvider(providerFunc{name: name, priority: priority, fn: fn})
 }
 
-// Priority bands for built-in providers (plugins pick their own).
+// Priority bands (providers pick their own; built-in feature packages use these).
 const (
-	PriorityCore    = 0  // log, config-derived
+	PriorityCore    = 0  // log
 	PriorityService = 50 // cache, storage, realtime, i18n
 	PriorityLate    = 90 // queue (depends on log)
 )
 
-// The built-in capabilities register themselves here — exactly like a plugin
-// would. Remove/override any of them with RegisterProvider.
+// Only the logger is a core default — it's foundational and always present.
+// All feature providers live in togo/providers/* and register themselves when
+// the project imports them.
 func init() {
 	RegisterProviderFunc("log", PriorityCore, func(k *Kernel) error { k.Log = newLogger(); return nil })
-	RegisterProviderFunc("i18n", PriorityService, func(k *Kernel) error {
-		k.I18n = i18n.Load(k.Config.LocaleDir, k.Config.Locale)
-		return nil
-	})
-	RegisterProviderFunc("cache", PriorityService, func(k *Kernel) error { k.Cache = cache.NewMemory(); return nil })
-	RegisterProviderFunc("storage", PriorityService, func(k *Kernel) error { k.Storage = storage.NewFS(k.Config.StorageDir); return nil })
-	RegisterProviderFunc("realtime", PriorityService, func(k *Kernel) error { k.Realtime = realtime.NewBroker(); return nil })
-	RegisterProviderFunc("queue", PriorityLate, func(k *Kernel) error {
-		k.Queue = queue.NewMemory(func(err error) { k.Log.Error("queue job failed", "err", err) })
-		return nil
-	})
 }
 
 // applyProviders runs every registered provider in ascending priority order.
@@ -81,7 +61,7 @@ func (k *Kernel) applyProviders() {
 	}
 }
 
-// Providers returns the names of registered providers in run order (for debugging).
+// Providers returns the names of registered providers in run order.
 func Providers() []string {
 	ps := append([]Provider(nil), providerRegistry...)
 	sort.SliceStable(ps, func(i, j int) bool { return ps[i].ProviderPriority() < ps[j].ProviderPriority() })

providers/cacheprovider/cacheprovider.go

@@ -0,0 +1,14 @@
+// Package cacheprovider registers the default in-memory cache. Blank-import to enable.
+package cacheprovider
+
+import (
+	"github.com/togo-framework/togo"
+	"github.com/togo-framework/togo/cache"
+)
+
+func init() {
+	togo.RegisterProviderFunc("cache", togo.PriorityService, func(k *togo.Kernel) error {
+		k.Cache = cache.NewMemory()
+		return nil
+	})
+}

providers/i18nprovider/i18nprovider.go

@@ -0,0 +1,14 @@
+// Package i18nprovider registers JSON-keyed translations. Blank-import to enable.
+package i18nprovider
+
+import (
+	"github.com/togo-framework/togo"
+	"github.com/togo-framework/togo/i18n"
+)
+
+func init() {
+	togo.RegisterProviderFunc("i18n", togo.PriorityService, func(k *togo.Kernel) error {
+		k.I18n = i18n.Load(k.Config.LocaleDir, k.Config.Locale)
+		return nil
+	})
+}

providers/queueprovider/queueprovider.go

@@ -0,0 +1,14 @@
+// Package queueprovider registers the in-process job queue. Blank-import to enable.
+package queueprovider
+
+import (
+	"github.com/togo-framework/togo"
+	"github.com/togo-framework/togo/queue"
+)
+
+func init() {
+	togo.RegisterProviderFunc("queue", togo.PriorityLate, func(k *togo.Kernel) error {
+		k.Queue = queue.NewMemory(func(err error) { k.Log.Error("queue job failed", "err", err) })
+		return nil
+	})
+}

providers/realtimeprovider/realtimeprovider.go

@@ -0,0 +1,14 @@
+// Package realtimeprovider registers the SSE realtime broker. Blank-import to enable.
+package realtimeprovider
+
+import (
+	"github.com/togo-framework/togo"
+	"github.com/togo-framework/togo/realtime"
+)
+
+func init() {
+	togo.RegisterProviderFunc("realtime", togo.PriorityService, func(k *togo.Kernel) error {
+		k.Realtime = realtime.NewBroker()
+		return nil
+	})
+}

providers/storageprovider/storageprovider.go

@@ -0,0 +1,14 @@
+// Package storageprovider registers filesystem storage. Blank-import to enable.
+package storageprovider
+
+import (
+	"github.com/togo-framework/togo"
+	"github.com/togo-framework/togo/storage"
+)
+
+func init() {
+	togo.RegisterProviderFunc("storage", togo.PriorityService, func(k *togo.Kernel) error {
+		k.Storage = storage.NewFS(k.Config.StorageDir)
+		return nil
+	})
+}