Changes needed before gokit/log to slog transition. (#39527)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #38889

PLEASE READ BELOW before looking at file changes

Before converting individual files/packages to slog, we generally need
to make these 2 changes to make the conversion easier:
- Replace uses of `kitlog.With` since they are not fully compatible with
our kitlog adapter
- Directly use the kitlog adapter logger type instead of the kitlog
interface, which will let us have direct access to the underlying slog
logger: `*logging.Logger`

Note: that I did not replace absolutely all uses of `kitlog.Logger`, but
I did remove all uses of `kitlog.With` except for these due to
complexity:
- server/logging/filesystem.go and the other log writers (webhook,
firehose, kinesis, lambda, pubsub, nats)
- server/datastore/mysql/nanomdm_storage.go (adapter pattern)
- server/vulnerabilities/nvd/* (cascades to CLI tools)
- server/service/osquery_utils/queries.go (callback type signatures
cascade broadly)
- cmd/maintained-apps/ (standalone, so can be transitioned later all at
once)

Most of the changes in this PR follow these patterns:
- `kitlog.Logger` type → `*logging.Logger`
- `kitlog.With(logger, ...)` → `logger.With(...)`
- `kitlog.NewNopLogger() → logging.NewNopLogger()`, including similar
variations such as `logging.NewLogfmtLogger(w)` and
`logging.NewJSONLogger(w)`
- removed many now-unused kitlog imports

Unique changes that the PR review should focus on:
- server/platform/logging/kitlog_adapter.go: Core adapter changes
- server/platform/logging/logging.go: New convenience functions
- server/service/integration_logger_test.go: Test changes for slog

# Checklist for submitter

If some of the following don't apply, delete the relevant line.

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
  - Was added in previous PR

## Testing

- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Refactor**
* Migrated the codebase to a unified internal structured logging system
for more consistent, reliable logs and observability.
* No user-facing functionality changed; runtime behavior and APIs remain
compatible.
* **Tests**
* Updated tests to use the new logging helpers to ensure consistent test
logging and validation.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

server/cron/calendar_cron.go

@@ -13,11 +13,10 @@ import (
 
 	"github.com/fleetdm/fleet/v4/server/config"
 	"github.com/fleetdm/fleet/v4/server/fleet"
+	"github.com/fleetdm/fleet/v4/server/platform/logging"
 	"github.com/fleetdm/fleet/v4/server/ptr"
 	"github.com/fleetdm/fleet/v4/server/service/calendar"
 	"github.com/fleetdm/fleet/v4/server/service/schedule"
-	"github.com/go-kit/log"
-	kitlog "github.com/go-kit/log"
 	"github.com/go-kit/log/level"
 	"github.com/google/uuid"
 )
@@ -33,12 +32,12 @@ func NewCalendarSchedule(
 	ds fleet.Datastore,
 	distributedLock fleet.Lock,
 	serverConfig config.CalendarConfig,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) (*schedule.Schedule, error) {
 	const (
 		name = string(fleet.CronCalendar)
 	)
-	logger = kitlog.With(logger, "cron", name)
+	logger = logger.With("cron", name)
 	s := schedule.New(
 		ctx, name, instanceID, serverConfig.Periodicity, ds, ds,
 		schedule.WithAltLockID("calendar"),
@@ -61,7 +60,7 @@ func NewCalendarSchedule(
 }
 
 func cronCalendarEvents(ctx context.Context, ds fleet.Datastore, distributedLock fleet.Lock, serverConfig config.CalendarConfig,
-	logger kitlog.Logger) error {
+	logger *logging.Logger) error {
 	appConfig, err := ds.AppConfig(ctx)
 	if err != nil {
 		return fmt.Errorf("load app config: %w", err)
@@ -108,7 +107,7 @@ func cronCalendarEventsForTeam(
 	team fleet.Team,
 	orgName string,
 	domain string,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) error {
 	if team.Config.Integrations.GoogleCalendar == nil ||
 		!team.Config.Integrations.GoogleCalendar.Enable {
@@ -128,7 +127,7 @@ func cronCalendarEventsForTeam(
 		return nil
 	}
 
-	logger = kitlog.With(logger, "team_id", team.ID)
+	logger = logger.With("team_id", team.ID)
 
 	//
 	// NOTEs:
@@ -208,7 +207,7 @@ func processCalendarFailingHosts(
 	calendarConfig *calendar.Config,
 	orgName string,
 	hosts []fleet.HostPolicyMembershipData,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) {
 	hosts = filterHostsWithSameEmail(hosts)
 
@@ -224,7 +223,7 @@ func processCalendarFailingHosts(
 			defer wg.Done()
 
 			for host := range hostsCh {
-				logger := log.With(logger, "host_id", host.HostID)
+				logger := logger.With("host_id", host.HostID)
 
 				hostCalendarEvent, calendarEvent, err := ds.GetHostCalendarEventByEmail(ctx, host.Email)
 
@@ -320,7 +319,7 @@ func processFailingHostExistingCalendarEvent(
 	host fleet.HostPolicyMembershipData,
 	policyIDtoPolicy *sync.Map,
 	calendarConfig *calendar.Config,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) error {
 
 	// Try to acquire the lock. Lock is needed to ensure calendar callback is not processed for this event at the same time.
@@ -512,7 +511,7 @@ func processFailingHostExistingCalendarEvent(
 }
 
 func getBodyTag(ctx context.Context, ds fleet.Datastore, host fleet.HostPolicyMembershipData, policyIDtoPolicy *sync.Map,
-	logger kitlog.Logger) string {
+	logger *logging.Logger) string {
 	var updatedBodyTag string
 	policyIDs := strings.Split(host.FailingPolicyIDs, ",")
 	if len(policyIDs) == 1 && policyIDs[0] != "" {
@@ -586,7 +585,7 @@ func processFailingHostCreateCalendarEvent(
 	orgName string,
 	host fleet.HostPolicyMembershipData,
 	policyIDtoPolicy *sync.Map,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) error {
 	calendarEvent, err := attemptCreatingEventOnUserCalendar(ctx, ds, orgName, host, userCalendar, policyIDtoPolicy, logger)
 	if err != nil {
@@ -608,7 +607,7 @@ func attemptCreatingEventOnUserCalendar(
 	host fleet.HostPolicyMembershipData,
 	userCalendar fleet.UserCalendar,
 	policyIDtoPolicy *sync.Map,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) (*fleet.CalendarEvent, error) {
 	year, month, today := time.Now().Date()
 	preferredDate := getPreferredCalendarEventDate(year, month, today)
@@ -668,7 +667,7 @@ func removeCalendarEventsFromPassingHosts(
 	ds fleet.Datastore,
 	calendarConfig *calendar.Config,
 	hosts []fleet.HostPolicyMembershipData,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) {
 	hostIDsByEmail := make(map[string][]uint)
 	for _, host := range hosts {
@@ -731,7 +730,7 @@ func removeCalendarEventsFromPassingHosts(
 func logHostsWithoutAssociatedEmail(
 	domain string,
 	hosts []fleet.HostPolicyMembershipData,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) {
 	if len(hosts) == 0 {
 		return
@@ -768,7 +767,7 @@ func isHostOnline(ctx context.Context, ds fleet.Datastore, hostID uint) (bool, e
 	}
 }
 
-func cronCalendarEventsCleanup(ctx context.Context, ds fleet.Datastore, logger kitlog.Logger) error {
+func cronCalendarEventsCleanup(ctx context.Context, ds fleet.Datastore, logger *logging.Logger) error {
 	appConfig, err := ds.AppConfig(ctx)
 	if err != nil {
 		return fmt.Errorf("load app config: %w", err)
@@ -833,7 +832,7 @@ func deleteAllCalendarEvents(
 	ds fleet.Datastore,
 	calendarConfig *calendar.Config,
 	teamID *uint,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) error {
 	calendarEvents, err := ds.ListCalendarEvents(ctx, teamID)
 	if err != nil {
@@ -845,7 +844,7 @@ func deleteAllCalendarEvents(
 
 func deleteCalendarEventsInParallel(
 	ctx context.Context, ds fleet.Datastore, calendarConfig *calendar.Config, calendarEvents []*fleet.CalendarEvent,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) {
 	if len(calendarEvents) > 0 {
 		calendarEventCh := make(chan *fleet.CalendarEvent)
@@ -879,7 +878,7 @@ func cleanupTeamCalendarEvents(
 	ds fleet.Datastore,
 	calendarConfig *calendar.Config,
 	team fleet.Team,
-	logger kitlog.Logger,
+	logger *logging.Logger,
 ) error {
 	teamFeatureEnabled := team.Config.Integrations.GoogleCalendar != nil && team.Config.Integrations.GoogleCalendar.Enable
 

server/cron/calendar_cron_test.go

@@ -16,9 +16,9 @@ import (
 	"github.com/fleetdm/fleet/v4/server/datastore/redis/redistest"
 	"github.com/fleetdm/fleet/v4/server/fleet"
 	"github.com/fleetdm/fleet/v4/server/mock"
+	"github.com/fleetdm/fleet/v4/server/platform/logging"
 	"github.com/fleetdm/fleet/v4/server/ptr"
 	"github.com/fleetdm/fleet/v4/server/service/redis_lock"
-	kitlog "github.com/go-kit/log"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -129,7 +129,7 @@ func TestEventForDifferentHost(t *testing.T) {
 	t.Parallel()
 	ds := new(mock.Store)
 	ctx := context.Background()
-	logger := kitlog.With(kitlog.NewLogfmtLogger(os.Stdout))
+	logger := logging.NewLogfmtLogger(os.Stdout)
 	ds.AppConfigFunc = func(ctx context.Context) (*fleet.AppConfig, error) {
 		return &fleet.AppConfig{
 			Integrations: fleet.Integrations{
@@ -208,7 +208,7 @@ func TestEventForDifferentHost(t *testing.T) {
 func TestCalendarEventsMultipleHosts(t *testing.T) {
 	ds := new(mock.Store)
 	ctx := context.Background()
-	logger := kitlog.With(kitlog.NewLogfmtLogger(os.Stdout))
+	logger := logging.NewLogfmtLogger(os.Stdout)
 	t.Cleanup(func() {
 		calendar.ClearMockEvents()
 		calendar.ClearMockChannels()
@@ -403,11 +403,11 @@ func (n notFoundErr) Error() string {
 func TestCalendarEvents1KHosts(t *testing.T) {
 	ds := new(mock.Store)
 	ctx := context.Background()
-	var logger kitlog.Logger
+	var logger *logging.Logger
 	if os.Getenv("CALENDAR_TEST_LOGGING") != "" {
-		logger = kitlog.With(kitlog.NewLogfmtLogger(os.Stdout))
+		logger = logging.NewLogfmtLogger(os.Stdout)
 	} else {
-		logger = kitlog.NewNopLogger()
+		logger = logging.NewNopLogger()
 	}
 	t.Cleanup(func() {
 		calendar.ClearMockEvents()
@@ -715,7 +715,7 @@ func TestCalendarEvents1KHosts(t *testing.T) {
 func TestEventBody(t *testing.T) {
 	ds := new(mock.Store)
 	ctx := context.Background()
-	logger := kitlog.With(kitlog.NewLogfmtLogger(os.Stdout))
+	logger := logging.NewLogfmtLogger(os.Stdout)
 	t.Cleanup(
 		func() {
 			calendar.ClearMockEvents()