🔐 fix: MCP OAuth Tool Discovery and Event Emission (#11599)

* fix: MCP OAuth tool discovery and event emission in event-driven mode

- Add discoverServerTools method to MCPManager for tool discovery when OAuth is required
- Fix OAuth event emission to send both ON_RUN_STEP and ON_RUN_STEP_DELTA events
- Fix hasSubscriber flag reset in GenerationJobManager for proper event buffering
- Add ToolDiscoveryOptions and ToolDiscoveryResult types
- Update reinitMCPServer to use new discovery method and propagate OAuth URLs

* refactor: Update ToolService and MCP modules for improved functionality

- Reintroduced Constants in ToolService for better reference management.
- Enhanced loadToolDefinitionsWrapper to handle both response and streamId scenarios.
- Updated MCP module to correct type definitions for oauthStart parameter.
- Improved MCPConnectionFactory to ensure proper disconnection handling during tool discovery.
- Adjusted tests to reflect changes in mock implementations and ensure accurate behavior during OAuth handling.

* fix: Refine OAuth handling in MCPConnectionFactory and related tests

- Updated the OAuth URL assignment logic in reinitMCPServer to prevent overwriting existing URLs.
- Enhanced error logging to provide clearer messages when tool discovery fails.
- Adjusted tests to reflect changes in OAuth handling, ensuring accurate detection of OAuth requirements without generating URLs in discovery mode.

* refactor: Clean up OAuth URL assignment in reinitMCPServer

- Removed redundant OAuth URL assignment logic in the reinitMCPServer function to streamline the tool discovery process.
- Enhanced error logging for tool discovery failures, improving clarity in debugging and monitoring.

* fix: Update response handling in ToolService for event-driven mode

- Changed the condition in loadToolDefinitionsWrapper to check for writableEnded instead of headersSent, ensuring proper event emission when the response is still writable.
- This adjustment enhances the reliability of event handling during tool execution, particularly in streaming scenarios.

packages/api/src/stream/GenerationJobManager.ts

@@ -238,6 +238,7 @@ class GenerationJobManagerClass {
       const currentRuntime = this.runtimeState.get(streamId);
       if (currentRuntime) {
         currentRuntime.syncSent = false;
+        currentRuntime.hasSubscriber = false;
         // Persist syncSent=false to Redis for cross-replica consistency
         this.jobStore.updateJob(streamId, { syncSent: false }).catch((err) => {
           logger.error(`[GenerationJobManager] Failed to persist syncSent=false:`, err);
@@ -435,6 +436,7 @@ class GenerationJobManagerClass {
       const currentRuntime = this.runtimeState.get(streamId);
       if (currentRuntime) {
         currentRuntime.syncSent = false;
+        currentRuntime.hasSubscriber = false;
         // Persist syncSent=false to Redis
         this.jobStore.updateJob(streamId, { syncSent: false }).catch((err) => {
           logger.error(`[GenerationJobManager] Failed to persist syncSent=false:`, err);
@@ -767,7 +769,6 @@ class GenerationJobManagerClass {
         for (const bufferedEvent of runtime.earlyEventBuffer) {
           onChunk(bufferedEvent);
         }
-        // Clear buffer after replay
         runtime.earlyEventBuffer = [];
       }
     }
@@ -822,7 +823,6 @@ class GenerationJobManagerClass {
     // Buffer early events if no subscriber yet (replay when first subscriber connects)
     if (!runtime.hasSubscriber) {
       runtime.earlyEventBuffer.push(event);
-      // Also emit to transport in case subscriber connects mid-flight
     }
 
     this.eventTransport.emitChunk(streamId, event);