fix: preserve collected data when controller script is interrupted by signal (#671)

When SIGINT is sent during flamegraph (or telemetry) collection, the
controller script handles it gracefully and outputs collected data before
exiting. However, the SSH process carrying the output gets interrupted by
perfspect's signal handler, returning exit code 255. Previously this
caused all collected data to be discarded.

Now, when the controller exit code is non-zero but stdout contains valid
controller output, the data is parsed and returned instead of being
treated as a fatal error.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: harp-intel

internal/script/script.go

@@ -137,8 +137,16 @@ func RunScripts(myTarget target.Target, scripts []ScriptDefinition, continueOnSc
 		return nil, err
 	}
 	if exitcode != 0 {
-		slog.Error("controller script returned non-zero exit code", slog.String("stdout", stdout), slog.String("stderr", stderr), slog.Int("exitcode", exitcode))
-		return nil, fmt.Errorf("controller script returned exit code %d", exitcode)
+		// If the controller was interrupted (e.g., by SIGINT) but still produced output,
+		// parse the output rather than discarding it. This handles the case where the
+		// controller's handle_sigint exits 0 but the SSH process carrying it gets
+		// interrupted and returns a non-zero exit code (e.g., 255).
+		if strings.Contains(stdout, "<---------------------->") {
+			slog.Warn("controller script returned non-zero exit code, but output is available and will be processed", slog.Int("exitcode", exitcode), slog.String("stderr", stderr))
+		} else {
+			slog.Error("controller script returned non-zero exit code", slog.String("stdout", stdout), slog.String("stderr", stderr), slog.Int("exitcode", exitcode))
+			return nil, fmt.Errorf("controller script returned exit code %d", exitcode)
+		}
 	}
 	// parse output of controller script
 	allScriptOutputs := parseControllerScriptOutput(stdout)