fix(prefixed_output): add flush to prevent losing final unterminated line

PrefixedOutput#print buffers partial lines until a newline is received.
When the last chunk from a stream does not end with \n (common with
Open3 popen2e EOF), that chunk was discarded. Add #flush to emit the
remaining buffer with the prefix, and call it at the end of all streaming
loops in SshRunner and WireGuardSetup.

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/hyperstack/state.rb b/lib/hyperstack/state.rb
index 0ce2687..a52b057 100644
--- a/lib/hyperstack/state.rb
+++ b/lib/hyperstack/state.rb
@@ -53,5 +53,12 @@ module HyperstackVM
         @mutex.synchronize { @delegate.print("#{@prefix}#{line}") }
       end
     end
+
+    def flush
+      return if @buffer.empty?
+
+      @mutex.synchronize { @delegate.print("#{@prefix}#{@buffer}") }
+      @buffer = +''
+    end
   end
 end