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.

3 files changed, 9 insertions, 0 deletions

diff --git a/lib/hyperstack/ssh_runner.rb b/lib/hyperstack/ssh_runner.rb
index e4440b6..1384109 100644
--- a/lib/hyperstack/ssh_runner.rb
+++ b/lib/hyperstack/ssh_runner.rb
@@ -25,6 +25,7 @@ module HyperstackVM
           combined << line
           @out.print(line)
         end
+        @out.flush
         return [combined, wait_thr.value]
       end
     end
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
diff --git a/lib/hyperstack/wireguard_setup.rb b/lib/hyperstack/wireguard_setup.rb
index 82a9dba..b2b7ec1 100644
--- a/lib/hyperstack/wireguard_setup.rb
+++ b/lib/hyperstack/wireguard_setup.rb
@@ -68,6 +68,7 @@ module HyperstackVM
         stdin.puts
         stdin.close
         output.each { |line| @out.print(line) }
+        @out.flush
         wait_thr.value
       end
     end