[core-be-agent] fix type mismatch: return sqlmock.Sqlmock (interface), not *sqlmock.Sqlmock

sqlmock.New() returns (Sqlmock, error) where Sqlmock is the interface
type, not a pointer. setupTestDB correctly returns sqlmock.Sqlmock (interface),
but setupWorkspaceCrudTest and setupInstructionsTestDB incorrectly declared
*sqlmock.Sqlmock (pointer to interface). In Go, *Interface is a distinct
type from Interface — this would be a compile error.

Root cause: copy-paste from setupWorkspaceCrudTest where the original author
assumed *sqlmock.Sqlmock was the correct type.

Fix: change both setup functions to return sqlmock.Sqlmock (interface) to
match what sqlmock.New() actually returns.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/handlers/instructions_test.go

@@ -29,7 +29,7 @@ import (
 // and returns both the mock and a gin engine that uses it.
 // The caller MUST use the returned gin engine for BOTH route registration
 // AND for r.ServeHTTP — using a different engine for either step breaks routing.
-func setupInstructionsTestDB(t *testing.T) (*sqlmock.Sqlmock, *gin.Engine) {
+func setupInstructionsTestDB(t *testing.T) (sqlmock.Sqlmock, *gin.Engine) {
 	gin.SetMode(gin.TestMode)
 	mockDB, mock, err := sqlmock.New()
 	if err != nil {
@@ -51,7 +51,7 @@ func setupInstructionsTestDB(t *testing.T) (*sqlmock.Sqlmock, *gin.Engine) {
 // setupInstructionsTest is kept for backward compatibility with tests that
 // don't need a gin engine (pure validation helpers). All DB-dependent tests
 // should use setupInstructionsTestDB instead.
-func setupInstructionsTest(t *testing.T) (*sqlmock.Sqlmock, *gin.Engine) {
+func setupInstructionsTest(t *testing.T) (sqlmock.Sqlmock, *gin.Engine) {
 	return setupInstructionsTestDB(t)
 }
 

workspace-server/internal/handlers/workspace_crud_test.go

@@ -27,7 +27,7 @@ import (
 //   - validateWorkspaceFields: newline rejection, YAML special chars, length.
 //   - validateWorkspaceDir: absolute/relative, traversal, system paths.
 
-func setupWorkspaceCrudTest(t *testing.T) (*sqlmock.Sqlmock, *gin.Engine) {
+func setupWorkspaceCrudTest(t *testing.T) (sqlmock.Sqlmock, *gin.Engine) {
 	gin.SetMode(gin.TestMode)
 	mock := setupTestDB(t)
 	r := gin.New()