fix(processing): reset completing flag on fallback failure, clean up empty catch

- completeWithCostOnlyLog now resets this.completing = false when
  the fallback itself fails, preventing a permanently stuck session
- Use _disconnectError in MCP test-connection to signal intentional ignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: waleedlatif1

apps/sim/app/api/mcp/servers/test-connection/route.ts

@@ -172,7 +172,7 @@ export const POST = withMcpAuth('write')(
         if (client) {
           try {
             await client.disconnect()
-          } catch (disconnectError) {}
+          } catch (_) {}
         }
       }
 

apps/sim/lib/logs/execution/logging-session.ts

@@ -879,6 +879,7 @@ export class LoggingSession {
         `[${this.requestId || 'unknown'}] Cost-only fallback succeeded for execution ${this.executionId}`
       )
     } catch (fallbackError) {
+      this.completing = false
       logger.error(
         `[${this.requestId || 'unknown'}] Cost-only fallback also failed for execution ${this.executionId}:`,
         { error: fallbackError instanceof Error ? fallbackError.message : String(fallbackError) }