Distribution/Features/Region/IRegionRepository.cs

@@ -6,6 +6,12 @@ public interface IRegionRepository
     Task<List<Models.Region>> GetAllAsync();
     Task<List<string>> GetAllCodesAsync();
     Task<bool> CodeExistsAsync(string code, Guid? excludeId = null);
+
+    Task<Models.User?> GetUserWithRoleAsync(Guid userId);
+    Task<List<Models.UserRegionScope>> GetManagerScopesAsync(Guid regionId);
+    Task<Models.UserRegionScope?> GetRegionScopeAsync(Guid userId, Guid regionId);
+    Task AddRegionScopeAsync(Models.UserRegionScope scope);
+    void RemoveRegionScopes(IEnumerable<Models.UserRegionScope> scopes);
     Task AddAsync(Models.Region entity);
     void Update(Models.Region entity);
     void Remove(Models.Region entity);

Distribution/Features/Region/RegionController.cs

@@ -43,6 +43,34 @@ public class RegionController(RegionService service) : ControllerBase
         return deleted ? NoContent() : NotFound();
     }
 
+    [HttpGet("{id:guid}/manager")]
+    public async Task<IActionResult> GetManager(Guid id)
+    {
+        var result = await service.GetManagerAsync(id);
+        return result is null ? NotFound() : Ok(result);
+    }
+
+    [HttpPut("{id:guid}/manager")]
+    public async Task<IActionResult> SetManager(Guid id, SetRegionManagerRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.SetManagerAsync(id, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex)
+        {
+            return BadRequest(new { error = ex.Message });
+        }
+    }
+
+    [HttpDelete("{id:guid}/manager")]
+    public async Task<IActionResult> RemoveManager(Guid id, CancellationToken ct)
+    {
+        var removed = await service.RemoveManagerAsync(id, ct);
+        return removed ? NoContent() : NotFound();
+    }
+
     //targets/budgets/agencies/tax-rule.
     [HttpPut("{id:guid}/manage")]
     public async Task<IActionResult> Manage(Guid id, ManageRegionRequest request, CancellationToken ct)

Distribution/Features/Region/RegionDTOs.cs

@@ -65,3 +65,9 @@ public record RegionManageEntryResponse(
     string? RuleConfig,
     Guid? AgencyUserId,
     DateTime CreatedAt);
+
+// Region manager = the single active user with the RegionalManager role scoped to the region
+// (UserRegionScope). Users themselves are owned by the auth service; this only links one to a region.
+public record SetRegionManagerRequest(Guid UserId);
+
+public record RegionManagerResponse(Guid RegionId, Guid UserId, string Username, string FullName);

Distribution/Features/Region/RegionRepository.cs

@@ -18,6 +18,25 @@ public class RegionRepository(AppDBContext context) : IRegionRepository
     public async Task<bool> CodeExistsAsync(string code, Guid? excludeId = null) =>
         await context.Regions.AnyAsync(r => r.Code == code && (excludeId == null || r.Id != excludeId));
 
+    public async Task<Models.User?> GetUserWithRoleAsync(Guid userId) =>
+        await context.Users.Include(u => u.Role).FirstOrDefaultAsync(u => u.Id == userId);
+
+    public async Task<List<Models.UserRegionScope>> GetManagerScopesAsync(Guid regionId) =>
+        await context.UserRegionScopes
+            .Include(s => s.User).ThenInclude(u => u.Role)
+            .Where(s => s.FK_RegionId == regionId && s.User.IsActive && s.User.Role.Name == "RegionalManager")
+            .ToListAsync();
+
+    public async Task<Models.UserRegionScope?> GetRegionScopeAsync(Guid userId, Guid regionId) =>
+        await context.UserRegionScopes.FirstOrDefaultAsync(s => s.FK_UserId == userId && s.FK_RegionId == regionId);
+
+    public async Task AddRegionScopeAsync(Models.UserRegionScope scope) =>
+        await context.UserRegionScopes.AddAsync(scope);
+
+    // Scope rows are hard-deleted (composite key user+region), same as UserRepository.ReplaceRegionScopesAsync.
+    public void RemoveRegionScopes(IEnumerable<Models.UserRegionScope> scopes) =>
+        context.UserRegionScopes.RemoveRange(scopes);
+
     public async Task AddAsync(Models.Region entity) =>
         await context.Regions.AddAsync(entity);
 

Distribution/Features/Region/RegionService.cs

@@ -91,6 +91,67 @@ public class RegionService(IRegionRepository repo, IUnitOfWork uow, ICurrentUser
         return new RegionResponse(region.Id, region.Code, region.Name, region.IsActive, region.CreatedAt);
     }
 
+    private const string RegionalManagerRole = "RegionalManager";
+
+    public async Task<RegionManagerResponse?> GetManagerAsync(Guid regionId)
+    {
+        var region = await repo.GetByIdAsync(regionId);
+        if (region is null || !region.IsActive) return null;
+        var scope = (await repo.GetManagerScopesAsync(regionId)).FirstOrDefault();
+        return scope is null ? null : new RegionManagerResponse(regionId, scope.FK_UserId, scope.User.Username, scope.User.FullName);
+    }
+
+    // A region has exactly one manager: assigning replaces any existing RegionalManager scoped to it.
+    // Returns null when the region does not exist; throws InvalidOperationException for an invalid user.
+    public async Task<RegionManagerResponse?> SetManagerAsync(Guid regionId, SetRegionManagerRequest request, CancellationToken ct = default)
+    {
+        var region = await repo.GetByIdAsync(regionId);
+        if (region is null || !region.IsActive) return null;
+
+        var user = await repo.GetUserWithRoleAsync(request.UserId);
+        if (user is null || !user.IsActive)
+            throw new InvalidOperationException("User not found.");
+        if (user.Role?.Name != RegionalManagerRole)
+            throw new InvalidOperationException($"User must have the {RegionalManagerRole} role to manage a region.");
+
+        await uow.BeginAsync(ct);
+        try
+        {
+            var existing = await repo.GetManagerScopesAsync(regionId);
+            repo.RemoveRegionScopes(existing.Where(s => s.FK_UserId != user.Id));
+            if (await repo.GetRegionScopeAsync(user.Id, regionId) is null)
+                await repo.AddRegionScopeAsync(new Models.UserRegionScope { FK_UserId = user.Id, FK_RegionId = regionId });
+            await uow.CommitAsync(ct);
+        }
+        catch
+        {
+            await uow.RollbackAsync(ct);
+            throw;
+        }
+        return new RegionManagerResponse(regionId, user.Id, user.Username, user.FullName);
+    }
+
+    public async Task<bool> RemoveManagerAsync(Guid regionId, CancellationToken ct = default)
+    {
+        var region = await repo.GetByIdAsync(regionId);
+        if (region is null || !region.IsActive) return false;
+        var existing = await repo.GetManagerScopesAsync(regionId);
+        if (existing.Count == 0) return false;
+
+        await uow.BeginAsync(ct);
+        try
+        {
+            repo.RemoveRegionScopes(existing);
+            await uow.CommitAsync(ct);
+        }
+        catch
+        {
+            await uow.RollbackAsync(ct);
+            throw;
+        }
+        return true;
+    }
+
     public async Task<bool> DeleteAsync(Guid id, CancellationToken ct = default)
     {
         var region = await repo.GetByIdAsync(id);