diff --git a/backend/internal/dav/service_dev.go b/backend/internal/dav/service_dev.go
index 1da9638..3d4d7a5 100644
--- a/backend/internal/dav/service_dev.go
+++ b/backend/internal/dav/service_dev.go
@@ -6,7 +6,6 @@ package dav
 import (
 	"context"
 	"fmt"
-	"log"
 	"os"
 
 	"github.com/jackc/pgx/v5/pgxpool"
@@ -20,13 +19,13 @@ func init() {
 		if os.Getenv("GO_TESTING") != "" {
 			return
 		}
-		log.Fatalf("failed to initialize dev service: %v", err)
+		panic("failed to initialize dev service: " + err.Error())
 	}
 }
 
 func connect() error {
 	dsn := fmt.Sprintf(
-		"postgres://%s:%s@localhost:5432/%s?sslmode=disable&require_auth=scram-sha-256",
+		"postgres://%s:%s@localhost:5432/%s?sslmode=disable&timezone=UTC&require_auth=scram-sha-256",
 		getEnv("POSTGRES_USER"),
 		getEnv("POSTGRES_PASSWORD"),
 		getEnv("POSTGRES_DB"),
diff --git a/backend/internal/dav/service_prod.go b/backend/internal/dav/service_prod.go
index 3159092..204c387 100644
--- a/backend/internal/dav/service_prod.go
+++ b/backend/internal/dav/service_prod.go
@@ -6,7 +6,6 @@ package dav
 import (
 	"context"
 	"fmt"
-	"log"
 	"os"
 
 	"github.com/jackc/pgx/v5/pgxpool"
@@ -20,13 +19,13 @@ func init() {
 		if os.Getenv("GO_TESTING") != "" {
 			return
 		}
-		log.Fatalf("failed to initialize prod service: %v", err)
+		panic("failed to initialize prod service: " + err.Error())
 	}
 }
 
 func connect() error {
 	dsn := fmt.Sprintf(
-		"postgres://%s:%s@%s:5432/%s?require_auth=scram-sha-256",
+		"postgres://%s:%s@%s:5432/%s?timezone=UTC&require_auth=scram-sha-256",
 		getEnv("POSTGRES_USER"),
 		getEnv("POSTGRES_PASSWORD"),
 		getEnv("POSTGRES_HOST"),
diff --git a/backend/internal/dav/shared.go b/backend/internal/dav/shared.go
index 02a5056..275ad08 100644
--- a/backend/internal/dav/shared.go
+++ b/backend/internal/dav/shared.go
@@ -1,6 +1,7 @@
 package dav
 
 import (
+	"crussell/clock"
 	"context"
 	"fmt"
 	"strings"
@@ -49,20 +50,20 @@ func (s *BaseService) ListEventsBetween(start, end time.Time) ([]CalendarEvent,
 }
 
 func (s *BaseService) ListEventsTomorrow() ([]CalendarEvent, error) {
-	now := time.Now()
-	tomorrow := time.Date(now.Year(), now.Month(), now.Day()+1, 0, 0, 0, 0, now.Location())
+	now := clock.Now()
+	tomorrow := time.Date(now.Year(), now.Month(), now.Day()+1, 0, 0, 0, 0, time.UTC)
 	dayAfter := tomorrow.Add(24 * time.Hour)
 	return s.ListEventsBetween(tomorrow, dayAfter)
 }
 
 func (s *BaseService) ListEventsThisWeek() ([]CalendarEvent, error) {
-	now := time.Now()
+	now := clock.Now()
 	weekday := int(now.Weekday())
 	if weekday == 0 { // Sunday
 		weekday = 7
 	}
 	monday := now.AddDate(0, 0, -weekday+1)
-	monday = time.Date(monday.Year(), monday.Month(), monday.Day(), 0, 0, 0, 0, now.Location())
+	monday = time.Date(monday.Year(), monday.Month(), monday.Day(), 0, 0, 0, 0, time.UTC)
 	sunday := monday.AddDate(0, 0, 7)
 	return s.ListEventsBetween(monday, sunday)
 }
@@ -107,7 +108,7 @@ func (s *BaseService) ListAllContacts() ([]Contact, error) {
 }
 
 func (s *BaseService) ListRecentContacts(days int) ([]Contact, error) {
-	cutoff := time.Now().AddDate(0, 0, -days).Unix()
+	cutoff := clock.Now().AddDate(0, 0, -days).Unix()
 	query := `SELECT id, addressbookid, uri, carddata, lastmodified, etag, size FROM dav_cards WHERE lastmodified >= $1 ORDER BY lastmodified DESC`
 	rows, err := s.db.Query(context.Background(), query, cutoff)
 	if err != nil {
@@ -172,15 +173,21 @@ func (s *BaseService) CreateContact(addressBookID int, userID string, input Cont
 		return nil // No DB configured, skip CardDAV sync
 	}
 
-	now := time.Now().Unix()
+	now := clock.Now().Unix()
 	uri := fmt.Sprintf("%s.vcf", userID)
 	cardData := GenerateVCard(input)
 
+	tx, err := s.db.Begin(context.Background())
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback(context.Background())
+
 	query := `
 		INSERT INTO dav_cards (addressbookid, uri, carddata, lastmodified, etag, size)
 		VALUES ($1, $2, $3, $4, $5, $6)
 	`
-	_, err := s.db.Exec(context.Background(), query,
+	_, err = tx.Exec(context.Background(), query,
 		addressBookID,
 		uri,
 		cardData,
@@ -188,42 +195,73 @@ func (s *BaseService) CreateContact(addressBookID int, userID string, input Cont
 		fmt.Sprintf("%d", now),
 		len(cardData),
 	)
-	return err
+	if err != nil {
+		return err
+	}
+
+	return tx.Commit(context.Background())
 }
 
 // UpdateContact updates an existing contact by URI
 func (s *BaseService) UpdateContact(addressBookID int, uri string, input ContactInput) error {
-	now := time.Now().Unix()
+	now := clock.Now().Unix()
 	cardData := GenerateVCard(input)
+
+	tx, err := s.db.Begin(context.Background())
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback(context.Background())
+
 	query := `
 		UPDATE dav_cards
 		SET carddata = $1, lastmodified = $2, etag = $3, size = $4
 		WHERE addressbookid = $5 AND uri = $6
 	`
-	_, err := s.db.Exec(context.Background(), query, cardData, now, fmt.Sprintf("%d", now), len(cardData), addressBookID, uri)
-	return err
+	_, err = tx.Exec(context.Background(), query, cardData, now, fmt.Sprintf("%d", now), len(cardData), addressBookID, uri)
+	if err != nil {
+		return err
+	}
+
+	return tx.Commit(context.Background())
 }
 
 // DeleteContact deletes a contact by URI
 func (s *BaseService) DeleteContact(addressBookID int, uri string) error {
+	tx, err := s.db.Begin(context.Background())
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback(context.Background())
+
 	query := `DELETE FROM dav_cards WHERE addressbookid = $1 AND uri = $2`
-	_, err := s.db.Exec(context.Background(), query, addressBookID, uri)
-	return err
+	_, err = tx.Exec(context.Background(), query, addressBookID, uri)
+	if err != nil {
+		return err
+	}
+
+	return tx.Commit(context.Background())
 }
 
 // CreateEvent adds a new event to a calendar
 func (s *BaseService) CreateEvent(calendarID int, input EventInput) error {
-	uid := fmt.Sprintf("%d@example.com", time.Now().UnixNano())
-	now := time.Now().Unix()
+	uid := fmt.Sprintf("%d@example.com", clock.Now().UnixNano())
+	now := clock.Now().Unix()
 	calendarData := GenerateICalEvent(input)
 
+	tx, err := s.db.Begin(context.Background())
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback(context.Background())
+
 	query := `
 		INSERT INTO dav_calendarobjects
 			(calendarid, uri, calendardata, lastmodified, etag, size, componenttype,
 			 firstoccurence, lastoccurence, uid)
 		VALUES ($1, $2, $3, $4, $5, $6, 'VEVENT', $7, $8, $9)
 	`
-	_, err := s.db.Exec(context.Background(), query,
+	_, err = tx.Exec(context.Background(), query,
 		calendarID,
 		uid+".ics",
 		calendarData,
@@ -234,33 +272,57 @@ func (s *BaseService) CreateEvent(calendarID int, input EventInput) error {
 		input.End.Unix(),
 		uid,
 	)
-	return err
+	if err != nil {
+		return err
+	}
+
+	return tx.Commit(context.Background())
 }
 
 // UpdateEvent updates an existing calendar event by UID
 func (s *BaseService) UpdateEvent(calendarID int, uid string, input EventInput) error {
-	now := time.Now().Unix()
+	now := clock.Now().Unix()
 	calendarData := GenerateICalEvent(input)
 
+	tx, err := s.db.Begin(context.Background())
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback(context.Background())
+
 	query := `
 		UPDATE dav_calendarobjects
 		SET calendardata = $1, lastmodified = $2, etag = $3, size = $4,
 		    firstoccurence = $5, lastoccurence = $6
 		WHERE calendarid = $7 AND uid = $8
 	`
-	_, err := s.db.Exec(context.Background(), query,
+	_, err = tx.Exec(context.Background(), query,
 		calendarData, now, fmt.Sprintf("%d", now), len(calendarData),
 		input.Start.Unix(), input.End.Unix(),
 		calendarID, uid,
 	)
-	return err
+	if err != nil {
+		return err
+	}
+
+	return tx.Commit(context.Background())
 }
 
 // DeleteEvent deletes an event by UID
 func (s *BaseService) DeleteEvent(calendarID int, uid string) error {
+	tx, err := s.db.Begin(context.Background())
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback(context.Background())
+
 	query := `DELETE FROM dav_calendarobjects WHERE calendarid = $1 AND uid = $2`
-	_, err := s.db.Exec(context.Background(), query, calendarID, uid)
-	return err
+	_, err = tx.Exec(context.Background(), query, calendarID, uid)
+	if err != nil {
+		return err
+	}
+
+	return tx.Commit(context.Background())
 }
 
 // ListEventsForContactSQL returns all calendar events where the given contact URI is an attendee (SQL optimized)
diff --git a/backend/internal/dav/types.go b/backend/internal/dav/types.go
index 8f87dd9..ccb848e 100644
--- a/backend/internal/dav/types.go
+++ b/backend/internal/dav/types.go
@@ -1,6 +1,7 @@
 package dav
 
 import (
+	"crussell/clock"
 	"fmt"
 	"time"
 )
@@ -81,18 +82,23 @@ type ContactInput struct {
 // Helper Functions
 // ============================================================================
 
-// GenerateICalEvent creates iCalendar format for UK timezone
+// GenerateICalEvent creates iCalendar format.
+// All times stored in the system are UTC equivalents of Europe/London
+// wall-clock times (e.g., 10:00 BST is stored as 09:00 UTC). The generated
+// iCal uses UTC-flagged DTSTART/DTEND (with Z suffix) so calendar apps
+// correctly display the intended wall-clock time regardless of the reader's
+// timezone.
 func GenerateICalEvent(input EventInput) string {
-	uid := fmt.Sprintf("%d@example.com", time.Now().UnixNano())
-	dtstamp := time.Now().UTC().Format("20060102T150405Z")
+	uid := fmt.Sprintf("%d@example.com", clock.Now().UnixNano())
+	dtstamp := clock.Now().UTC().Format("20060102T150405Z")
 
 	var dtstart, dtend string
 	if input.AllDay {
 		dtstart = fmt.Sprintf("DTSTART;VALUE=DATE:%s", input.Start.Format("20060102"))
 		dtend = fmt.Sprintf("DTEND;VALUE=DATE:%s", input.End.Format("20060102"))
 	} else {
-		dtstart = fmt.Sprintf("DTSTART;TZID=Europe/London:%s", input.Start.Format("20060102T150405"))
-		dtend = fmt.Sprintf("DTEND;TZID=Europe/London:%s", input.End.Format("20060102T150405"))
+		dtstart = fmt.Sprintf("DTSTART:%sZ", input.Start.UTC().Format("20060102T150405"))
+		dtend = fmt.Sprintf("DTEND:%sZ", input.End.UTC().Format("20060102T150405"))
 	}
 
 	// Build attendees section
@@ -105,23 +111,6 @@ func GenerateICalEvent(input EventInput) string {
 VERSION:2.0
 PRODID:-//Your App//EN
 CALSCALE:GREGORIAN
-BEGIN:VTIMEZONE
-TZID:Europe/London
-BEGIN:DAYLIGHT
-TZOFFSETFROM:+0000
-TZOFFSETTO:+0100
-TZNAME:BST
-DTSTART:19700329T010000
-RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
-END:DAYLIGHT
-BEGIN:STANDARD
-TZOFFSETFROM:+0100
-TZOFFSETTO:+0000
-TZNAME:GMT
-DTSTART:19701025T020000
-RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
-END:STANDARD
-END:VTIMEZONE
 BEGIN:VEVENT
 UID:%s
 DTSTAMP:%s
@@ -161,7 +150,7 @@ END:VCARD`,
 		input.Email,
 		input.Phone,
 		input.DOB,
-		time.Now().UTC().Format("20060102T150405Z"))
+		clock.Now().UTC().Format("20060102T150405Z"))
 
 	return vcard
 }
diff --git a/backend/internal/s3/s3.go b/backend/internal/s3/s3.go
index 6f2fe5c..567da22 100644
--- a/backend/internal/s3/s3.go
+++ b/backend/internal/s3/s3.go
@@ -18,6 +18,7 @@ type Uploader interface {
 	Download(ctx context.Context, bucket, key string, w io.Writer) error
 	Delete(ctx context.Context, bucket, key string) error
 	GetURL(ctx context.Context, bucket, key string) (string, error)
+	HealthCheck(ctx context.Context) error
 }
 
 type S3Client struct {
@@ -65,6 +66,15 @@ func (s *S3Client) GetURL(ctx context.Context, bucket, key string) (string, erro
 	return fmt.Sprintf("%s/%s/%s", s.publicURL, bucket, key), nil
 }
 
+func (s *S3Client) HealthCheck(_ context.Context) error {
+	if s.endpoint == "" {
+		return fmt.Errorf("S3 client not initialized: R2_ENDPOINT not set")
+	}
+	// Production stub — can't perform a real check without the SDK.
+	// Actual operations (Upload, Download, Delete) will return errors.
+	return nil
+}
+
 func getEnv(key, fallback string) string {
 	if val := os.Getenv(key); val != "" {
 		return val
@@ -72,6 +82,5 @@ func getEnv(key, fallback string) string {
 	if fallback != "" {
 		return fallback
 	}
-	log.Fatal("FATAL: Environment variable not set:", key)
-	return ""
+	panic("Environment variable not set: " + key)
 }
diff --git a/backend/internal/s3/s3_dev.go b/backend/internal/s3/s3_dev.go
index a88ec2e..3aeb712 100644
--- a/backend/internal/s3/s3_dev.go
+++ b/backend/internal/s3/s3_dev.go
@@ -23,6 +23,7 @@ type Uploader interface {
 	Download(ctx context.Context, bucket, key string, w io.Writer) error
 	Delete(ctx context.Context, bucket, key string) error
 	GetURL(ctx context.Context, bucket, key string) (string, error)
+	HealthCheck(ctx context.Context) error
 }
 
 type S3Client struct {
@@ -202,3 +203,13 @@ func (s *S3Client) Delete(ctx context.Context, bucket, key string) error {
 func (s *S3Client) GetURL(ctx context.Context, bucket, key string) (string, error) {
 	return fmt.Sprintf("%s/%s/%s", s.publicURL, bucket, key), nil
 }
+
+func (s *S3Client) HealthCheck(ctx context.Context) error {
+	_, err := s.client.HeadBucket(ctx, &s3.HeadBucketInput{
+		Bucket: aws.String(s.bucket),
+	})
+	if err != nil {
+		return fmt.Errorf("S3 bucket %q is not accessible (check S3_PUBLIC_URL / RUSTFS_ENDPOINT config): %w", s.bucket, err)
+	}
+	return nil
+}
diff --git a/backend/internal/square/square_dev.go b/backend/internal/square/square_dev.go
index c948443..33013ff 100644
--- a/backend/internal/square/square_dev.go
+++ b/backend/internal/square/square_dev.go
@@ -4,6 +4,7 @@
 package square
 
 import (
+	"crussell/clock"
 	"context"
 	"fmt"
 	"log"
@@ -85,7 +86,7 @@ func (m *MockClient) CreatePayment(ctx context.Context, req CreatePaymentReq) (*
 	m.mu.Lock()
 	defer m.mu.Unlock()
 
-	paymentID := fmt.Sprintf("pay_mock_%d", time.Now().UnixNano())
+	paymentID := fmt.Sprintf("pay_mock_%d", clock.Now().UnixNano())
 	fees := req.Amount*14/1000 + 25 // online rate: 1.4% + 25p
 
 	result := &PaymentResult{
@@ -107,7 +108,7 @@ func (m *MockClient) CreatePayment(ctx context.Context, req CreatePaymentReq) (*
 func (m *MockClient) CreateCheckout(ctx context.Context, req CreateCheckoutReq) (*CheckoutResult, error) {
 	log.Printf("[SQUARE-MOCK] CreateCheckout: amount=%d, tipEnabled=%v, reference=%s", req.Amount, req.TipEnabled, req.ReferenceID)
 
-	checkoutID := fmt.Sprintf("chk_mock_%d", time.Now().UnixNano())
+	checkoutID := fmt.Sprintf("chk_mock_%d", clock.Now().UnixNano())
 	result := &CheckoutResult{
 		ID:     checkoutID,
 		Status: "PENDING",
@@ -118,12 +119,17 @@ func (m *MockClient) CreateCheckout(ctx context.Context, req CreateCheckoutReq)
 	m.mu.Unlock()
 
 	go func() {
+		defer func() {
+			if r := recover(); r != nil {
+				log.Printf("Panic recovered in Square mock payment processing: %v", r)
+			}
+		}()
 		mockSleep(3 * time.Second)
 
 		m.mu.Lock()
 		defer m.mu.Unlock()
 
-		paymentID := fmt.Sprintf("pay_%d", time.Now().UnixNano())
+		paymentID := fmt.Sprintf("pay_%d", clock.Now().UnixNano())
 		amount := req.Amount
 		tipAmount := int64(0)
 		if req.TipEnabled {
@@ -184,7 +190,7 @@ func (m *MockClient) RefundPayment(ctx context.Context, req RefundPaymentReq) (*
 	m.mu.Lock()
 	defer m.mu.Unlock()
 
-	refundID := fmt.Sprintf("ref_mock_%d", time.Now().UnixNano())
+	refundID := fmt.Sprintf("ref_mock_%d", clock.Now().UnixNano())
 	amount := req.Amount
 	if amount == 0 {
 		if payment, ok := m.payments[req.PaymentID]; ok {
@@ -212,7 +218,7 @@ func (m *MockClient) CreateCardOnFile(ctx context.Context, userID, cardToken str
 		m.cards[userID] = make(map[string]*CardOnFile)
 	}
 
-	cardID := fmt.Sprintf("mock_card_%d", time.Now().UnixNano())
+	cardID := fmt.Sprintf("mock_card_%d", clock.Now().UnixNano())
 	card := &CardOnFile{
 		ID:          cardID,
 		CardID:      "cfa_" + cardID,
@@ -220,7 +226,7 @@ func (m *MockClient) CreateCardOnFile(ctx context.Context, userID, cardToken str
 		Last4:       "4242",
 		ExpMonth:    12,
 		ExpYear:     2030,
-		Fingerprint: fmt.Sprintf("fp_%d", time.Now().UnixNano()),
+		Fingerprint: fmt.Sprintf("fp_%d", clock.Now().UnixNano()),
 		IsDefault:   len(m.cards[userID]) == 0,
 	}
 	m.cards[userID][cardID] = card
@@ -238,7 +244,7 @@ func (m *MockClient) CreateCardOnFileRaw(ctx context.Context, userID, cardNumber
 		m.cards[userID] = make(map[string]*CardOnFile)
 	}
 
-	cardID := fmt.Sprintf("mock_card_%d", time.Now().UnixNano())
+	cardID := fmt.Sprintf("mock_card_%d", clock.Now().UnixNano())
 	last4 := cardNumber[len(cardNumber)-4:]
 	brands := map[string]string{"4": "VISA", "5": "MASTERCARD", "3": "AMEX", "6": "DISCOVER"}
 	brand := brands[string(cardNumber[0])]
@@ -253,7 +259,7 @@ func (m *MockClient) CreateCardOnFileRaw(ctx context.Context, userID, cardNumber
 		Last4:       last4,
 		ExpMonth:    expMonth,
 		ExpYear:     expYear,
-		Fingerprint: fmt.Sprintf("fp_%d", time.Now().UnixNano()),
+		Fingerprint: fmt.Sprintf("fp_%d", clock.Now().UnixNano()),
 		IsDefault:   len(m.cards[userID]) == 0,
 	}
 	m.cards[userID][cardID] = card