fix: soft-fail MCP server connection errors instead of throwing (#485)

When both transports (streamable HTTP + SSE) fail to connect to an
external MCP server, the error was thrown and double-logged via
logHttpError (which emits log.exception for 500s), causing noisy
alerts in Mezmo during bug duty.

Now connectMCPClient returns null on all connection failures (matching
the existing timeout behavior) and logs via log.softFail instead.
This eliminates double-logging since all callers already handle null
returns gracefully.

Author: MQ37

src/mcp/client.ts

@@ -5,7 +5,7 @@ import { StreamableHTTPClientTransport } from '@modelcontextprotocol/sdk/client/
 import log from '@apify/log';
 
 import { TimeoutError } from '../errors.js';
-import { logHttpError } from '../utils/logging.js';
+import { getHttpStatusCode } from '../utils/logging.js';
 import { ACTORIZED_MCP_CONNECTION_TIMEOUT_MSEC } from './const.js';
 import { getMCPServerID } from './utils.js';
 
@@ -16,10 +16,8 @@ import { getMCPServerID } from './utils.js';
 export async function connectMCPClient(
     url: string, token: string, mcpSessionId?: string,
 ): Promise<Client | null> {
-    let client: Client;
     try {
-        client = await createMCPStreamableClient(url, token);
-        return client;
+        return await createMCPStreamableClient(url, token);
     } catch (error) {
         // If streamable HTTP transport fails on not timeout error, continue with SSE transport
         if (error instanceof TimeoutError) {
@@ -34,15 +32,21 @@ export async function connectMCPClient(
     }
 
     try {
-        client = await createMCPSSEClient(url, token);
-        return client;
+        return await createMCPSSEClient(url, token);
     } catch (error) {
         if (error instanceof TimeoutError) {
             log.warning('Connection to MCP server using SSE transport timed out', { url, mcpSessionId });
             return null;
         }
-        logHttpError(error, 'Failed to connect to MCP server using SSE transport', { url, mcpSessionId, cause: error });
-        throw error;
+        // External MCP server unavailability is operational, not a bug in our service
+        const statusCode = getHttpStatusCode(error);
+        log.softFail('Failed to connect to MCP server using SSE transport', {
+            url,
+            mcpSessionId,
+            statusCode,
+            error: error instanceof Error ? error.message : String(error),
+        });
+        return null;
     }
 }