perf(admin): cache the suspension gate lookup

The suspension gate runs CurrentSuspension on every authenticated request. Add a write-through in-memory cache on account.Store keyed by account id, invalidated on Suspend/LiftSuspension, with the cached entry re-evaluated against the wall clock so a temporary block lapses without an explicit invalidation. Single-instance, matching the deployment (one shared Store). Keeps the gate off the database on the hot path while a block still takes effect on the next request.

backend/internal/account/suspension.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"sync"
 	"time"
 
 	"github.com/go-jet/jet/v2/postgres"
@@ -82,6 +83,7 @@ func (s *Store) Suspend(ctx context.Context, accountID uuid.UUID, until *time.Ti
 	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
 		return Suspension{}, fmt.Errorf("account: suspend %s: %w", accountID, err)
 	}
+	s.invalidateSuspension(accountID)
 	return modelToSuspension(row), nil
 }
 
@@ -100,6 +102,7 @@ func (s *Store) LiftSuspension(ctx context.Context, accountID uuid.UUID) error {
 	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
 		return fmt.Errorf("account: lift suspension %s: %w", accountID, err)
 	}
+	s.invalidateSuspension(accountID)
 	return nil
 }
 
@@ -115,6 +118,30 @@ func (s *Store) CurrentSuspension(ctx context.Context, accountID uuid.UUID) (Sus
 		return Suspension{}, false, nil
 	}
 	now := time.Now().UTC()
+	if s.suspensions != nil {
+		if e, ok := s.suspensions.get(accountID); ok {
+			if !e.found {
+				return Suspension{}, false, nil // cached: not blocked
+			}
+			if suspensionActiveAt(e.susp, now) {
+				return e.susp, true, nil // cached block still in force
+			}
+			// The cached block has lapsed since it was cached; refresh from the database below.
+		}
+	}
+	susp, found, err := s.queryCurrentSuspension(ctx, accountID, now)
+	if err != nil {
+		return Suspension{}, false, err
+	}
+	if s.suspensions != nil {
+		s.suspensions.put(accountID, suspensionCacheEntry{susp: susp, found: found})
+	}
+	return susp, found, nil
+}
+
+// queryCurrentSuspension reads the account's strongest in-force block straight from the database
+// (no cache), as of now. It backs CurrentSuspension on a cache miss or a lapsed entry.
+func (s *Store) queryCurrentSuspension(ctx context.Context, accountID uuid.UUID, now time.Time) (Suspension, bool, error) {
 	stmt := postgres.SELECT(table.AccountSuspensions.AllColumns).
 		FROM(table.AccountSuspensions).
 		WHERE(
@@ -134,6 +161,61 @@ func (s *Store) CurrentSuspension(ctx context.Context, accountID uuid.UUID) (Sus
 	return modelToSuspension(row), true, nil
 }
 
+// invalidateSuspension drops the account's cached block so the next CurrentSuspension re-reads it.
+// Called after Suspend and LiftSuspension.
+func (s *Store) invalidateSuspension(accountID uuid.UUID) {
+	if s.suspensions != nil {
+		s.suspensions.invalidate(accountID)
+	}
+}
+
+// suspensionActiveAt reports whether a suspension is in force at now: permanent, or not yet
+// expired. The lifted check is implicit — only non-lifted blocks are ever cached or returned.
+func suspensionActiveAt(susp Suspension, now time.Time) bool {
+	return susp.BlockedUntil == nil || susp.BlockedUntil.After(now)
+}
+
+// suspensionCache is the gate's write-through cache of each account's current block, keyed by
+// account id. The suspension gate reads it on every authenticated request; Suspend and
+// LiftSuspension invalidate the account's entry. An entry holds the strongest active block at
+// query time (or a not-blocked marker), re-evaluated against the wall clock on read, so a
+// temporary block lapses without an explicit invalidation. It is single-instance, matching the
+// deployment (one shared Store); a multi-instance deployment would need a shared cache.
+type suspensionCache struct {
+	mu sync.RWMutex
+	m  map[uuid.UUID]suspensionCacheEntry
+}
+
+// suspensionCacheEntry is a cached lookup: the strongest active block when found, else a
+// not-blocked marker (found=false).
+type suspensionCacheEntry struct {
+	susp  Suspension
+	found bool
+}
+
+func newSuspensionCache() *suspensionCache {
+	return &suspensionCache{m: make(map[uuid.UUID]suspensionCacheEntry)}
+}
+
+func (c *suspensionCache) get(id uuid.UUID) (suspensionCacheEntry, bool) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	e, ok := c.m[id]
+	return e, ok
+}
+
+func (c *suspensionCache) put(id uuid.UUID, e suspensionCacheEntry) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.m[id] = e
+}
+
+func (c *suspensionCache) invalidate(id uuid.UUID) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	delete(c.m, id)
+}
+
 // activeSuspensionPredicate matches the rows of a block that is in force at now: not lifted and
 // either permanent or not yet expired.
 func activeSuspensionPredicate(now time.Time) postgres.BoolExpression {