feat: harden support, localize knowledge and add operator availability [skip ci]

Source-only publication of reviewed commit 64e96a7f423673dc29ad56485be9fc79bce8af1c.

Passed in isolation: focused frontend/backend tests, race checks, TypeScript typecheck, lint, Go compilation, Flowgram build, and deterministic SDK build/tests.

Not accepted as a production release: Next.js export/native assembly remains blocked by environment memory limits; browser interaction and MySQL staging acceptance remain unverified. No production server, database/schema, runtime configuration, deployment, release tag, or workflow execution was performed.

Expected source tree: 0a4a7528e9.

internal/repositories/customer_identity_repository.go

@@ -1,3 +1,5 @@
+// Modified in the independent hardening fork; see docs/hardening.
+
 package repositories
 
 import (
@@ -6,7 +8,6 @@ import (
 
 	"agent-desk/internal/pkg/httpx/params"
 
-	"github.com/mlogclub/simple/common/strs"
 	"github.com/mlogclub/simple/sqls"
 	"gorm.io/gorm"
 )
@@ -36,14 +37,13 @@ func (r *customerIdentityRepository) Take(db *gorm.DB, where ...interface{}) *mo
 	return ret
 }
 
-// GetBy 按外部来源 + 外部用户标识查询身份映射（与 uk_customer_external 一致）。
+// GetBy is the legacy/internal-integration lookup. Ambiguous mappings fail closed.
 func (r *customerIdentityRepository) GetBy(db *gorm.DB, externalSource enums.ExternalSource, externalID string) *models.CustomerIdentity {
-	if strs.IsAnyBlank(string(externalSource), externalID) {
+	identity, err := r.GetUniqueBy(db, "", externalSource, externalID)
+	if err != nil {
 		return nil
 	}
-	return r.FindOne(db, sqls.NewCnd().
-		Eq("external_source", externalSource).
-		Eq("external_id", externalID))
+	return identity
 }
 
 func (r *customerIdentityRepository) FindByCustomerID(db *gorm.DB, customerID int64) []models.CustomerIdentity {