Add intake worker

Subsystem to monitor IMAP mailbox for new messages.

Introduces:
- intake: worker that uses IDLE or polling to detect new emails.
- imap: client wrapper for connection management and IMAP commands.
- filter: logic for IMAP search and sender allow-list.
- tracker: concurrency control to prevent processing the same UID twice.
- backoff: for handling connection retries with jitter.

internal/imap/imap_test.go

@@ -0,0 +1,224 @@
+package imap
+
+import (
+	"log/slog"
+	"testing"
+
+	"raven/internal/filter"
+)
+
+func TestConfigAddress(t *testing.T) {
+	tests := []struct {
+		name string
+		cfg  Config
+		want string
+	}{
+		{
+			name: "standard config",
+			cfg:  Config{Host: "imap.example.com", Port: "993"},
+			want: "imap.example.com:993",
+		},
+		{
+			name: "empty host",
+			cfg:  Config{Host: "", Port: "993"},
+			want: ":993",
+		},
+		{
+			name: "empty port",
+			cfg:  Config{Host: "imap.example.com", Port: ""},
+			want: "imap.example.com:",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := tt.cfg.Address(); got != tt.want {
+				t.Errorf(
+					"Address() = %q, want %q",
+					got, tt.want,
+				)
+			}
+		})
+	}
+}
+
+func TestConfigValidate(t *testing.T) {
+	tests := []struct {
+		name    string
+		cfg     Config
+		wantErr string
+	}{
+		{
+			name: "valid config",
+			cfg: Config{
+				Host:     "imap.example.com",
+				Password: "secret",
+				Port:     "993",
+				User:     "user@example.com",
+			},
+			wantErr: "",
+		},
+		{
+			name: "missing host",
+			cfg: Config{
+				Password: "secret",
+				Port:     "993",
+				User:     "user@example.com",
+			},
+			wantErr: "missing host",
+		},
+		{
+			name: "missing password",
+			cfg: Config{
+				Host: "imap.example.com",
+				Port: "993",
+				User: "user@example.com",
+			},
+			wantErr: "missing password",
+		},
+		{
+			name: "missing port",
+			cfg: Config{
+				Host:     "imap.example.com",
+				Password: "secret",
+				User:     "user@example.com",
+			},
+			wantErr: "missing port",
+		},
+		{
+			name: "missing user",
+			cfg: Config{
+				Host:     "imap.example.com",
+				Password: "secret",
+				Port:     "993",
+			},
+			wantErr: "missing user",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.cfg.Validate()
+			if tt.wantErr == "" {
+				if err != nil {
+					t.Errorf(
+						"Validate() unexpected error: %v",
+						err,
+					)
+				}
+				return
+			}
+			if err == nil {
+				t.Errorf(
+					"Validate() expected error containing %q, got nil",
+					tt.wantErr,
+				)
+				return
+			}
+			if got := err.Error(); got != tt.wantErr {
+				t.Errorf(
+					"Validate() error = %q, want %q",
+					got, tt.wantErr,
+				)
+			}
+		})
+	}
+}
+
+func TestNewClient(t *testing.T) {
+	validCfg := Config{
+		Host:     "imap.example.com",
+		Password: "secret",
+		Port:     "993",
+		User:     "user@example.com",
+	}
+
+	tests := []struct {
+		name    string
+		cfg     Config
+		filters filter.Filters
+		wantErr bool
+	}{
+		{
+			name:    "valid config",
+			cfg:     validCfg,
+			filters: filter.Filters{},
+			wantErr: false,
+		},
+		{
+			name: "valid config with filters",
+			cfg:  validCfg,
+			filters: filter.Filters{
+				Subject: "test",
+				To:      "recipient@example.com",
+				Body:    []string{"keyword"},
+			},
+			wantErr: false,
+		},
+		{
+			name:    "invalid config",
+			cfg:     Config{Host: "imap.example.com"},
+			filters: filter.Filters{},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			client, err := NewClient(
+				tt.cfg, tt.filters, slog.Default(),
+			)
+			if tt.wantErr {
+				if err == nil {
+					t.Error(
+						"NewClient() expected error, got nil",
+					)
+				}
+				return
+			}
+			if err != nil {
+				t.Errorf(
+					"NewClient() unexpected error: %v", err,
+				)
+				return
+			}
+			if client == nil {
+				t.Error("NewClient() returned nil client")
+				return
+			}
+			// Verify client is not connected.
+			if client.Client() != nil {
+				t.Error(
+					"NewClient() client should not be connected",
+				)
+			}
+		})
+	}
+}
+
+func TestClientNotConnected(t *testing.T) {
+	cfg := Config{
+		Host:     "imap.example.com",
+		Password: "secret",
+		Port:     "993",
+		User:     "user@example.com",
+	}
+	client, err := NewClient(cfg, filter.Filters{}, slog.Default())
+	if err != nil {
+		t.Fatalf("NewClient() unexpected error: %v", err)
+	}
+
+	t.Run("Fetch without connection", func(t *testing.T) {
+		_, err := client.Fetch(1, true)
+		if err == nil {
+			t.Error("Fetch() expected error when not connected")
+		}
+	})
+
+	t.Run("MarkSeen without connection", func(t *testing.T) {
+		err := client.MarkSeen(1)
+		if err == nil {
+			t.Error("MarkSeen() expected error when not connected")
+		}
+	})
+}