Logger: the version line once per service name

Every Logger construction printed the version line, and a rugnux run makes a
logger per FFT indexer of its first-pass ladder: about 180 version lines in a
20 s live run. The line now goes out the first time a service name is seen.
The set is a function-local static, as jfjoch_writer's logger is a global
made before this file's own namespace-scope statics.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HVeDQsU5a8AJUdJPgWevAK

common/Logger.cpp

@@ -7,6 +7,7 @@
 #include "spdlog/fmt/bin_to_hex.h"
 
 #include <map>
+#include <set>
 
 #include "Logger.h"
 #include "GitInfo.h"
@@ -64,6 +65,15 @@ Logger::Logger(const std::string &service_name, const std::string &file_name) {
     spdlog_logger = std::make_shared<spdlog::logger>(service_name, std::begin(sinks), std::end(sinks));
     if (const auto it = service_levels.find(service_name); it != service_levels.end())
         spdlog_logger->set_level(it->second);
+    {
+        // The version line goes out once per service: a run makes many loggers of one service (every FFT indexer
+        // is one). Function-local, as a static Logger (jfjoch_writer's) is made before this file's own statics.
+        static std::mutex version_mutex;
+        static std::set<std::string> version_logged;
+        std::unique_lock ul(version_mutex);
+        if (!version_logged.insert(service_name).second)
+            return;
+    }
     if (jfjoch_git_sha1().empty())
         spdlog_logger->info("Version {} {}", jfjoch_version(), variant);
     else