feat(core): mount the configuration extension point on the kernel Context

Context 新增 Config() 访问器，注册表随 Fork 共享（配置声明是进程级事实），
并在 types.go 导出配置别名与 ConfigGatedPlugin 可选接口，为插件门禁做准备。

backend/core/config_test.go

@@ -72,3 +72,21 @@ func TestConfigGetRejectsNilView(t *testing.T) {
 	_, err := core.ConfigGet[float64](nil, "otel.sampling_rate")
 	require.ErrorIs(t, err, extpoints.ErrConfigNotResolved)
 }
+
+func TestContextConfigIsSharedAcrossForks(t *testing.T) {
+	ctx := core.NewContext(nil)
+	child := ctx.Fork()
+
+	require.NotNil(t, ctx.Config())
+	assert.Same(t, ctx.Config(), child.Config(), "configuration declarations are process-wide facts")
+
+	require.NoError(t, child.Config().Declare("cache",
+		extpoints.ConfigBinding{Prefix: "otel", Target: &otelConfig{}}))
+
+	declared := false
+	for _, entry := range ctx.Config().Entries() {
+		declared = declared || entry.Key == "otel.sampling_rate"
+	}
+	assert.True(t, declared, "a declaration made in a plugin scope must be visible to the root")
+	assert.False(t, ctx.Config().Resolved())
+}

backend/core/context.go

@@ -27,6 +27,7 @@ type Context struct {
 	tasks      extpoints.TaskExtension
 	schedules  extpoints.ScheduleExtension
 	settings   extpoints.SettingExtension
+	config     extpoints.ConfigExtension
 
 	mu        sync.RWMutex
 	children  []*Context
@@ -56,6 +57,7 @@ func NewContext(base context.Context) *Context {
 		tasks:      extpoints.NewTaskRegistry(),
 		schedules:  extpoints.NewScheduleRegistry(),
 		settings:   extpoints.NewSettingRegistry(),
+		config:     extpoints.NewConfigRegistry(nil),
 		values:     make(map[any]any),
 	}
 }
@@ -167,6 +169,7 @@ func (c *Context) ForkWithContext(base context.Context) *Context {
 		tasks:      c.tasks,
 		schedules:  c.schedules,
 		settings:   c.settings,
+		config:     c.config,
 		values:     make(map[any]any),
 	}
 
@@ -235,6 +238,13 @@ func (c *Context) Setting() extpoints.SettingExtension {
 	return c.Settings()
 }
 
+// Config returns the process-level configuration extension point. The registry is
+// shared by every fork because configuration declarations are global facts, and it
+// carries no per-scope disposers: values are resolved once before Apply runs.
+func (c *Context) Config() extpoints.ConfigExtension {
+	return c.config
+}
+
 // OnDispose registers a cleanup callback function to be executed when this Context is disposed.
 // It accepts func() error, func(), or Disposer.
 func (c *Context) OnDispose(fn any) {

backend/core/types.go

@@ -154,3 +154,32 @@ type SettingExtension = extpoints.SettingExtension
 
 // SettingSchema re-exports extpoints.SettingSchema.
 type SettingSchema = extpoints.SettingSchema
+
+// ConfigExtension re-exports extpoints.ConfigExtension.
+type ConfigExtension = extpoints.ConfigExtension
+
+// ConfigSource re-exports extpoints.ConfigSource.
+type ConfigSource = extpoints.ConfigSource
+
+// ConfigBinding re-exports extpoints.ConfigBinding.
+type ConfigBinding = extpoints.ConfigBinding
+
+// ConfigView re-exports extpoints.ConfigView.
+type ConfigView = extpoints.ConfigView
+
+// ConfigEntry re-exports extpoints.ConfigEntry.
+type ConfigEntry = extpoints.ConfigEntry
+
+// ConfigGatedPlugin is an optional interface for plugins whose activation depends on
+// configuration. The kernel evaluates the gate during reconciliation, before the
+// plugin's Apply runs, so every key read by ConfigEnabled must be published through
+// DeclareConfig.
+type ConfigGatedPlugin interface {
+	Plugin
+
+	// DeclareConfig publishes the configuration bindings consumed by ConfigEnabled.
+	DeclareConfig() []extpoints.ConfigBinding
+
+	// ConfigEnabled reports whether this plugin should activate for the resolved values.
+	ConfigEnabled(view extpoints.ConfigView) bool
+}