# Concelier Deprecation Headers Middleware

## Module
Concelier

## Status
VERIFIED

## Description
HTTP deprecation headers middleware for Concelier API endpoints, signaling API version lifecycle to consumers. Not in the known list.

## Implementation Details
- **Modules**: `src/Concelier/StellaOps.Concelier.WebService/Deprecation/`
- **Key Classes**:
  - `DeprecationMiddleware` (`src/Concelier/StellaOps.Concelier.WebService/Deprecation/DeprecationMiddleware.cs`) - ASP.NET Core middleware that adds HTTP deprecation headers to responses
  - `DeprecationMiddlewareExtensions` (`src/Concelier/StellaOps.Concelier.WebService/Deprecation/DeprecationMiddleware.cs`) - extension methods for middleware registration
  - `DeprecationMiddlewareRegistration` (`src/Concelier/StellaOps.Concelier.WebService/Deprecation/DeprecationMiddleware.cs`) - DI registration helpers
- **Source**: Sprint 0116 (batch_14/file_17.md)

## E2E Test Plan
- [x] Call a deprecated API endpoint and verify the response includes `Deprecation` and `Sunset` HTTP headers
- [x] Call a non-deprecated endpoint and verify no deprecation headers are present
- [x] Verify the deprecation date format conforms to RFC 7231
- [x] Verify middleware registration: confirm `DeprecationMiddleware` is in the ASP.NET Core pipeline

## Verification
- **Run ID**: run-001
- **Date**: 2026-02-13
- **Result**: PASS - WebService.Tests 215/215 passed. 9 targeted DeprecationHeadersTests verify HTTP deprecation headers for 5 legacy endpoints (LegacyLinksets, LegacyAdvisoryObservations, LegacyAdvisoryLinksets, LegacyAdvisoryLinksetsExport, LegacyConcelierObservations), migration guide presence for all deprecated endpoints, sunset date ordering (sunset after deprecation), and header constant definitions.