diff --git a/components/claw_modules/claw_core/src/claw_core_events.c b/components/claw_modules/claw_core/src/claw_core_events.c
index 274aa0ab4..803186e45 100644
--- a/components/claw_modules/claw_core/src/claw_core_events.c
+++ b/components/claw_modules/claw_core/src/claw_core_events.c
@@ -302,9 +302,11 @@ void claw_core_publish_stage_tool_calls(const claw_core_request_t *request,
         const char *name = response->tool_calls[i].name ? response->tool_calls[i].name : "?";
         const char *args = response->tool_calls[i].arguments_json;
         if (args && args[0]) {
-            written = snprintf(buf + off, sizeof(buf) - off, "%s%s(%.40s%s)",
-                               i == 0 ? "" : ", ", name, args,
-                               strlen(args) > 40 ? "..." : "");
+            size_t arg_len = strlen(args);
+            size_t prefix_len = utf8_prefix_len(args, 40);
+            written = snprintf(buf + off, sizeof(buf) - off, "%s%s(%.*s%s)",
+                               i == 0 ? "" : ", ", name, (int)prefix_len, args,
+                               arg_len > prefix_len ? "..." : "");
         } else {
             written = snprintf(buf + off, sizeof(buf) - off, "%s%s",
                                i == 0 ? "" : ", ", name);
diff --git a/components/claw_modules/claw_manager/src/claw_agent_mgr.c b/components/claw_modules/claw_manager/src/claw_agent_mgr.c
index da3f9158d..3e40a4586 100644
--- a/components/claw_modules/claw_manager/src/claw_agent_mgr.c
+++ b/components/claw_modules/claw_manager/src/claw_agent_mgr.c
@@ -643,9 +643,13 @@ static void claw_agent_mgr_completion_observer(const claw_core_completion_summar
     if ((size_t)written >= sizeof(text)) {
         size_t suffix_len = strlen(truncated_suffix);
         if (suffix_len + 1U < sizeof(text)) {
-            strlcpy(text + sizeof(text) - suffix_len - 1U,
-                    truncated_suffix,
-                    suffix_len + 1U);
+            size_t p = sizeof(text) - suffix_len - 1U;
+            /* Back off so the suffix never splices into the middle of a
+             * multi-byte UTF-8 sequence, which would emit invalid bytes. */
+            while (p > 0 && ((unsigned char)text[p] & 0xC0) == 0x80) {
+                p--;
+            }
+            strlcpy(text + p, truncated_suffix, sizeof(text) - p);
         }
     }