feat(module): add four-phase Module interface and registry

internal/module/registry.go

@@ -0,0 +1,56 @@
+package module
+
+import (
+	"fmt"
+	"sort"
+	"sync"
+)
+
+// Registry holds all known modules keyed by Meta.ID.
+type Registry struct {
+	mu      sync.RWMutex
+	modules map[string]Module
+}
+
+// NewRegistry returns an empty registry.
+func NewRegistry() *Registry {
+	return &Registry{modules: make(map[string]Module)}
+}
+
+// Register adds a module. Returns an error if the ID is already present
+// or empty. Safe for concurrent use.
+func (r *Registry) Register(m Module) error {
+	id := m.Meta().ID
+	if id == "" {
+		return fmt.Errorf("module has empty ID")
+	}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if _, dup := r.modules[id]; dup {
+		return fmt.Errorf("module %q already registered", id)
+	}
+	r.modules[id] = m
+	return nil
+}
+
+// Get returns the module with the given ID, or (nil, false) if absent.
+func (r *Registry) Get(id string) (Module, bool) {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	m, ok := r.modules[id]
+	return m, ok
+}
+
+// All returns all registered modules sorted by ID for determinism.
+func (r *Registry) All() []Module {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	out := make([]Module, 0, len(r.modules))
+	for _, m := range r.modules {
+		out = append(out, m)
+	}
+	sort.Slice(out, func(i, j int) bool {
+		return out[i].Meta().ID < out[j].Meta().ID
+	})
+	return out
+}