diff --git a/db/migrations/0003_cleanup_indexes.sql b/db/migrations/0003_cleanup_indexes.sql
new file mode 100644
index 0000000..29f7968
--- /dev/null
+++ b/db/migrations/0003_cleanup_indexes.sql
@@ -0,0 +1,17 @@
+CREATE INDEX IF NOT EXISTS idx_sessions_state_expires
+    ON sessions (state, expires_at);
+
+CREATE INDEX IF NOT EXISTS idx_grants_session_id
+    ON grants (session_id);
+
+CREATE INDEX IF NOT EXISTS idx_grants_state_expires
+    ON grants (state, expires_at);
+
+CREATE INDEX IF NOT EXISTS idx_approvals_state_expires
+    ON approvals (state, expires_at);
+
+CREATE INDEX IF NOT EXISTS idx_artifacts_state_expires
+    ON artifacts (state, expires_at);
+
+CREATE INDEX IF NOT EXISTS idx_audit_events_created_at
+    ON audit_events (created_at);
diff --git a/internal/store/postgres/repository.go b/internal/store/postgres/repository.go
index 30f838c..7c0faae 100644
--- a/internal/store/postgres/repository.go
+++ b/internal/store/postgres/repository.go
@@ -137,12 +137,16 @@ func (r *Repository) GetSession(ctx context.Context, sessionID string) (*core.Se
 	return &session, nil
 }
 
+const maxGrantsBySessionLookup = 10000
+
 func (r *Repository) ListGrantsBySession(ctx context.Context, sessionID string) ([]*core.Grant, error) {
 	rows, err := r.db.Query(ctx, `
 		SELECT id, tenant_id, session_id, tool, capability, resource_ref, delivery_mode, connector_kind, approval_id, artifact_ref, state, requested_ttl_seconds, effective_ttl_seconds, expires_at, created_at, reason
 		FROM grants
 		WHERE session_id = $1
-	`, sessionID)
+		ORDER BY created_at ASC, id ASC
+		LIMIT $2
+	`, sessionID, maxGrantsBySessionLookup)
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/store/postgres/repository_test.go b/internal/store/postgres/repository_test.go
index 6a23003..87c9474 100644
--- a/internal/store/postgres/repository_test.go
+++ b/internal/store/postgres/repository_test.go
@@ -110,3 +110,41 @@ func TestRepository_UseArtifactMarksSingleUse(t *testing.T) {
 		t.Fatalf("artifact state = %q, want %q", artifact.State, core.ArtifactStateUsed)
 	}
 }
+
+func TestRepository_ListGrantsBySessionIsBounded(t *testing.T) {
+	t.Parallel()
+
+	mock, err := pgxmock.NewPool()
+	if err != nil {
+		t.Fatalf("pgxmock.NewPool() error = %v", err)
+	}
+	defer mock.Close()
+
+	repo := postgres.NewRepository(mock)
+	createdAt := time.Date(2026, 4, 15, 18, 0, 0, 0, time.UTC)
+	expiresAt := createdAt.Add(30 * time.Minute)
+
+	mock.ExpectQuery("SELECT id, tenant_id, session_id, tool, capability, resource_ref, delivery_mode, connector_kind, approval_id, artifact_ref, state, requested_ttl_seconds, effective_ttl_seconds, expires_at, created_at, reason\\s+FROM grants\\s+WHERE session_id = \\$1\\s+ORDER BY created_at ASC, id ASC\\s+LIMIT \\$2").
+		WithArgs("sess_abc", pgxmock.AnyArg()).
+		WillReturnRows(pgxmock.NewRows([]string{
+			"id", "tenant_id", "session_id", "tool", "capability", "resource_ref", "delivery_mode", "connector_kind", "approval_id", "artifact_ref", "state", "requested_ttl_seconds", "effective_ttl_seconds", "expires_at", "created_at", "reason",
+		}).AddRow(
+			"gr_123", "t_acme", "sess_abc", "github", "repo.read", "repo:evalops/asb", "direct", "github", nil, nil,
+			string(core.GrantStateIssued), int32(300), int32(300), expiresAt, createdAt, "cleanup",
+		))
+
+	grants, err := repo.ListGrantsBySession(context.Background(), "sess_abc")
+	if err != nil {
+		t.Fatalf("ListGrantsBySession() error = %v", err)
+	}
+	if len(grants) != 1 {
+		t.Fatalf("len(grants) = %d, want 1", len(grants))
+	}
+	if grants[0].ID != "gr_123" {
+		t.Fatalf("grant id = %q, want %q", grants[0].ID, "gr_123")
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Fatalf("ExpectationsWereMet() error = %v", err)
+	}
+}