refactor!: introduce generic processors registry and remove normalize registry adapter

- add new `processors` package with canonical `Processor` interface
- add `processors.Registry` with Register/Build/BuildChain factory model
- switch `pipeline.Pipeline` to `[]processors.Processor`
- replace `normalize.Registry` + registry adapter with direct `normalize.Processor`
- remove `normalize/registry.go`
- update root docs to position normalize as one optional processing stage
- add tests for processors registry, normalize processor behavior, and pipeline flow

BREAKING CHANGE:
- `pipeline.Processor` removed; use `processors.Processor`
- `normalize.Registry` and old normalize processor adapter APIs removed
- downstream daemons must update processor wiring to new `processors.Registry`
  and `normalize.NewProcessor(...)`

processors/doc.go

@@ -0,0 +1,22 @@
+// Package processors defines feedkit's generic processor abstraction and registry.
+//
+// Processors are optional pipeline stages that can transform, drop, or reject
+// events before dispatch to sinks.
+//
+// Registry provides name-based construction so daemons can assemble processor
+// chains without embedding switch statements in wiring code.
+//
+// Example:
+//
+//	reg := processors.NewRegistry()
+//	reg.Register("normalize", func() (processors.Processor, error) {
+//	    return normalize.NewProcessor(myNormalizers, false), nil
+//	})
+//
+//	chain, err := reg.BuildChain([]string{"normalize"})
+//	if err != nil {
+//	    // handle wiring error
+//	}
+//
+//	p := &pipeline.Pipeline{Processors: chain}
+package processors

processors/processor.go

@@ -0,0 +1,15 @@
+package processors
+
+import (
+	"context"
+
+	"gitea.maximumdirect.net/ejr/feedkit/event"
+)
+
+// Processor can mutate/drop events (dedupe, rate-limit, normalization tweaks).
+type Processor interface {
+	Process(ctx context.Context, in event.Event) (out *event.Event, err error)
+}
+
+// Factory constructs a configured Processor instance.
+type Factory func() (Processor, error)

processors/registry.go

@@ -0,0 +1,71 @@
+package processors
+
+import (
+	"fmt"
+	"strings"
+)
+
+type Registry struct {
+	byDriver map[string]Factory
+}
+
+func NewRegistry() *Registry {
+	return &Registry{byDriver: map[string]Factory{}}
+}
+
+// Register associates a processor driver name with a factory.
+//
+// Register panics for empty driver names, nil factories, and duplicates.
+func (r *Registry) Register(driver string, f Factory) {
+	if r == nil {
+		panic("processors.Registry.Register: registry cannot be nil")
+	}
+	driver = strings.TrimSpace(driver)
+	if driver == "" {
+		panic("processors.Registry.Register: driver cannot be empty")
+	}
+	if f == nil {
+		panic(fmt.Sprintf("processors.Registry.Register: factory cannot be nil (driver=%q)", driver))
+	}
+	if r.byDriver == nil {
+		r.byDriver = map[string]Factory{}
+	}
+	if _, exists := r.byDriver[driver]; exists {
+		panic(fmt.Sprintf("processors.Registry.Register: driver %q already registered", driver))
+	}
+	r.byDriver[driver] = f
+}
+
+// Build constructs a Processor by driver name.
+func (r *Registry) Build(driver string) (Processor, error) {
+	if r == nil {
+		return nil, fmt.Errorf("processors registry is nil")
+	}
+	driver = strings.TrimSpace(driver)
+	f, ok := r.byDriver[driver]
+	if !ok {
+		return nil, fmt.Errorf("unknown processor driver: %q", driver)
+	}
+
+	p, err := f()
+	if err != nil {
+		return nil, fmt.Errorf("build processor %q: %w", driver, err)
+	}
+	if p == nil {
+		return nil, fmt.Errorf("build processor %q: factory returned nil processor", driver)
+	}
+	return p, nil
+}
+
+// BuildChain constructs an ordered processor chain from a driver list.
+func (r *Registry) BuildChain(drivers []string) ([]Processor, error) {
+	out := make([]Processor, 0, len(drivers))
+	for i, driver := range drivers {
+		p, err := r.Build(driver)
+		if err != nil {
+			return nil, fmt.Errorf("build processor chain[%d] (%q): %w", i, strings.TrimSpace(driver), err)
+		}
+		out = append(out, p)
+	}
+	return out, nil
+}

processors/registry_test.go

@@ -0,0 +1,100 @@
+package processors
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/ejr/feedkit/event"
+)
+
+type testProcessor struct {
+	name string
+}
+
+func (p testProcessor) Process(context.Context, event.Event) (*event.Event, error) {
+	return nil, nil
+}
+
+func TestRegistryRegisterValidation(t *testing.T) {
+	t.Run("empty driver panics", func(t *testing.T) {
+		r := NewRegistry()
+		assertPanics(t, func() {
+			r.Register("   ", func() (Processor, error) { return testProcessor{name: "x"}, nil })
+		})
+	})
+
+	t.Run("nil factory panics", func(t *testing.T) {
+		r := NewRegistry()
+		assertPanics(t, func() {
+			r.Register("normalize", nil)
+		})
+	})
+
+	t.Run("duplicate driver panics", func(t *testing.T) {
+		r := NewRegistry()
+		r.Register("normalize", func() (Processor, error) { return testProcessor{name: "a"}, nil })
+		assertPanics(t, func() {
+			r.Register("normalize", func() (Processor, error) { return testProcessor{name: "b"}, nil })
+		})
+	})
+}
+
+func TestRegistryBuildUnknownDriver(t *testing.T) {
+	r := NewRegistry()
+	_, err := r.Build("does_not_exist")
+	if err == nil {
+		t.Fatalf("expected error for unknown driver")
+	}
+	if !strings.Contains(err.Error(), "unknown processor driver") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestRegistryBuildChainPreservesOrder(t *testing.T) {
+	r := NewRegistry()
+	r.Register("first", func() (Processor, error) { return testProcessor{name: "first"}, nil })
+	r.Register("second", func() (Processor, error) { return testProcessor{name: "second"}, nil })
+
+	chain, err := r.BuildChain([]string{"first", "second"})
+	if err != nil {
+		t.Fatalf("BuildChain error: %v", err)
+	}
+	if len(chain) != 2 {
+		t.Fatalf("expected 2 processors, got %d", len(chain))
+	}
+
+	p0, ok := chain[0].(testProcessor)
+	if !ok || p0.name != "first" {
+		t.Fatalf("unexpected chain[0]: %#v", chain[0])
+	}
+	p1, ok := chain[1].(testProcessor)
+	if !ok || p1.name != "second" {
+		t.Fatalf("unexpected chain[1]: %#v", chain[1])
+	}
+}
+
+func TestRegistryBuildChainIndexedFailure(t *testing.T) {
+	r := NewRegistry()
+	r.Register("ok", func() (Processor, error) { return testProcessor{name: "ok"}, nil })
+	r.Register("broken", func() (Processor, error) { return nil, errors.New("boom") })
+
+	_, err := r.BuildChain([]string{"ok", "broken"})
+	if err == nil {
+		t.Fatalf("expected error")
+	}
+	if !strings.Contains(err.Error(), "chain[1]") {
+		t.Fatalf("expected indexed error, got: %v", err)
+	}
+}
+
+func assertPanics(t *testing.T, fn func()) {
+	t.Helper()
+	defer func() {
+		if recover() == nil {
+			t.Fatalf("expected panic")
+		}
+	}()
+	fn()
+}