perf(protocol): skip string debug escaping when proto debug is off

output_escape() was called on every send_str/receive_str even when
LOG_DEBUG_PROTO logging was disabled, allocating and scanning the whole
payload for a line that log_debug_message() then discarded.  Add a
log_debug_enabled(flag) gate mirroring log_debug_message()'s own filter and
check it before escaping.  Redacted (secret) strings still log the same
<redacted> marker; no observable log output changes.

src/shared/log.c

@@ -27,6 +27,10 @@ uint32_t get_log_debug_flags(void) {
   return current_debug_flags;
 }
 
+bool log_debug_enabled(LogDebugFlag flag) {
+  return current_log_level <= LOG_LEVEL_DEBUG && (current_debug_flags & flag) != 0;
+}
+
 void set_log_info_flags(uint32_t flags) {
   info_flags = flags;
   info_flags_explicit = true;

src/shared/log.h

@@ -29,6 +29,10 @@ void log_perror(const char* context);
 void set_log_level(LogLevel level);
 void set_log_debug_flags(uint32_t flags);
 uint32_t get_log_debug_flags(void);
+/* True when a log_debug_message() call with the same flag would actually emit:
+ * the debug log level is enabled AND the flag is selected.  Hot paths use this
+ * to skip expensive message formatting/escaping when the line is filtered. */
+bool log_debug_enabled(LogDebugFlag flag);
 void log_debug_message(LogDebugFlag flag, const char* message, ...);
 void set_log_info_flags(uint32_t flags);
 uint32_t get_log_info_flags(void);

src/shared/protocol.c

@@ -432,7 +432,7 @@ static bool protocol_send_str_impl(ProtocolSession* session, const char* data, b
     return false;
   if (redact) {
     log_debug_message(LOG_DEBUG_PROTO, "Send String: <redacted>");
-  } else {
+  } else if (log_debug_enabled(LOG_DEBUG_PROTO)) {
     char* escaped_data = output_escape(data, log_get_8_bit_output());
     log_debug_message(LOG_DEBUG_PROTO, "Send String: %s",
                       escaped_data ? escaped_data : "<allocation failed>");
@@ -465,7 +465,7 @@ static char* protocol_receive_str_impl(ProtocolSession* session, bool redact) {
   data[size] = '\0';
   if (redact) {
     log_debug_message(LOG_DEBUG_PROTO, "Received String: <redacted>");
-  } else {
+  } else if (log_debug_enabled(LOG_DEBUG_PROTO)) {
     char* escaped_data = output_escape(data, log_get_8_bit_output());
     log_debug_message(LOG_DEBUG_PROTO, "Received String: %s",
                       escaped_data ? escaped_data : "<allocation failed>");

tests/test_log.c

@@ -128,6 +128,25 @@ static void test_log_message_formats() {
   EXPECT_TRUE(true);
 }
 
+/* log_debug_enabled is the lazy-formatting gate for log_debug_message: it must
+ * be true only at DEBUG level with the requested flag selected, exactly
+ * mirroring the filter inside log_debug_message itself. */
+static void test_log_debug_enabled_matches_gate() {
+  set_log_level(LOG_LEVEL_WARNING);
+  set_log_debug_flags(LOG_DEBUG_ALL);
+  EXPECT_FALSE(log_debug_enabled(LOG_DEBUG_PROTO));
+
+  set_log_level(LOG_LEVEL_DEBUG);
+  set_log_debug_flags(LOG_DEBUG_PROTO);
+  EXPECT_TRUE(log_debug_enabled(LOG_DEBUG_PROTO));
+  EXPECT_FALSE(log_debug_enabled(LOG_DEBUG_IO));
+
+  set_log_debug_flags(0);
+  EXPECT_FALSE(log_debug_enabled(LOG_DEBUG_PROTO));
+
+  set_log_debug_flags(LOG_DEBUG_ALL);
+}
+
 void test_log() {
   test_log_message_debug();
   test_log_message_info();
@@ -139,4 +158,5 @@ void test_log() {
   test_log_filtering();
   test_log_stderr_mode_all();
   test_log_message_formats();
+  test_log_debug_enabled_matches_gate();
 }