Report the shutdown from the batch loop, not the signal handler

src/main.zig

@@ -221,9 +221,10 @@ fn printStatus(comptime fmt: []const u8, args: anytype) void {
     };
 }
 
+// Only the atomic store: a log here would rebind the shared stderr writer under
+// the interrupted call and can block on the stderr lock. The batch loop reports it.
 fn handleShutdownSignal(_: posix.SIG) callconv(.c) void {
     shutdown_requested.store(true, .seq_cst);
-    std.log.info("Shutdown signal received, initiating graceful shutdown...", .{});
 }
 
 fn setupSignalHandlers() void {

src/processor/processor.zig

@@ -403,6 +403,9 @@ pub const Processor = struct {
             }
         }
 
+        // The signal handler only sets the flag, so the acknowledgement comes from here.
+        std.log.info("Shutdown requested, finishing the process...", .{});
+
         // Graceful stop: cancel and await the worker (runs its final flush/commit)
         // before reporting the stream stopped.
         flush_future.cancel(io);