🏷️ feat: Request Placeholders for Custom Endpoint & MCP Headers (#9095)

* feat: Add conversation ID support to custom endpoint headers

- Add LIBRECHAT_CONVERSATION_ID to customUserVars when provided
- Pass conversation ID to header resolution for dynamic headers
- Add comprehensive test coverage

Enables custom endpoints to access conversation context using {{LIBRECHAT_CONVERSATION_ID}} placeholder.

* fix: filter out unresolved placeholders from headers (thanks @MrunmayS)

* feat: add support for request body placeholders in custom endpoint headers

- Add {{LIBRECHAT_BODY_*}} placeholders for conversationId, parentMessageId, messageId
- Update tests to reflect new body placeholder functionality

* refactor resolveHeaders

* style: minor styling cleanup

* fix: type error in unit test

* feat: add body to other endpoints

* feat: add body for mcp tool calls

* chore: remove changes that unnecessarily increase scope after clarification of requirements

* refactor: move http.ts to packages/api and have RequestBody intersect with Express request body

* refactor: processMCPEnv now uses single object argument pattern

* refactor: update processMCPEnv to use 'options' parameter and align types across MCP connection classes

* feat: enhance MCP connection handling with dynamic request headers to pass request body fields

---------

Co-authored-by: Gopal Sharma <gopalsharma@gopal.sharma1>
Co-authored-by: s10gopal <36487439+s10gopal@users.noreply.github.com>
Co-authored-by: Dustin Healy <dustinhealy1@gmail.com>

api/server/cleanup.js

@@ -1,6 +1,6 @@
-const { logger } = require('~/config');
+const { logger } = require('@librechat/data-schemas');
 
-// WeakMap to hold temporary data associated with requests
+/** WeakMap to hold temporary data associated with requests */
 const requestDataMap = new WeakMap();
 
 const FinalizationRegistry = global.FinalizationRegistry || null;
@@ -23,7 +23,7 @@ const clientRegistry = FinalizationRegistry
         } else {
           logger.debug('[FinalizationRegistry] Cleaning up client');
         }
-      } catch (e) {
+      } catch {
         // Ignore errors
       }
     })
@@ -55,6 +55,9 @@ function disposeClient(client) {
     if (client.responseMessageId) {
       client.responseMessageId = null;
     }
+    if (client.parentMessageId) {
+      client.parentMessageId = null;
+    }
     if (client.message_file_map) {
       client.message_file_map = null;
     }
@@ -334,7 +337,7 @@ function disposeClient(client) {
       }
     }
     client.options = null;
-  } catch (e) {
+  } catch {
     // Ignore errors during disposal
   }
 }