diff --git a/mateclaw-server/src/main/resources/application-mysql.yml b/mateclaw-server/src/main/resources/application-mysql.yml
index 9bdd2af4..da3c7491 100644
--- a/mateclaw-server/src/main/resources/application-mysql.yml
+++ b/mateclaw-server/src/main/resources/application-mysql.yml
@@ -5,7 +5,12 @@ spring:
     # 自动创建的库用了 server 默认字符集也不会影响数据。要求 DB user 具备 CREATE 权限（默认 root 可）。
     # 如果使用受限账号，请提前手工执行：
     #   CREATE DATABASE mateclaw CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
-    url: jdbc:mysql://${DB_HOST:localhost}:${DB_PORT:3306}/${DB_NAME:mateclaw}?createDatabaseIfNotExist=true&useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai&allowPublicKeyRetrieval=true
+    # characterEncoding=utf8mb4 + connectionCollation=utf8mb4_unicode_ci force
+    # the JDBC connection to negotiate 4-byte UTF-8 end-to-end. With 3-byte
+    # `utf8` the driver rejects emoji and CJK supplementary-plane chars even
+    # when the table charset is utf8mb4, surfacing as
+    # `Data truncation: Incorrect string value` on assistant message INSERT.
+    url: jdbc:mysql://${DB_HOST:localhost}:${DB_PORT:3306}/${DB_NAME:mateclaw}?createDatabaseIfNotExist=true&useUnicode=true&characterEncoding=utf8mb4&connectionCollation=utf8mb4_unicode_ci&useSSL=false&serverTimezone=Asia/Shanghai&allowPublicKeyRetrieval=true
     driver-class-name: com.mysql.cj.jdbc.Driver
     username: ${DB_USERNAME:root}
     password: ${DB_PASSWORD:mateclaw123}
diff --git a/mateclaw-server/src/main/resources/db/migration/h2/V91__widen_message_and_skill_content.sql b/mateclaw-server/src/main/resources/db/migration/h2/V91__widen_message_and_skill_content.sql
new file mode 100644
index 00000000..42e6fe6e
--- /dev/null
+++ b/mateclaw-server/src/main/resources/db/migration/h2/V91__widen_message_and_skill_content.sql
@@ -0,0 +1,7 @@
+-- V91: Mirror MySQL widening of mate_message.content / content_parts and
+-- mate_skill.skill_content. H2's TEXT is already CLOB (effectively unbounded)
+-- so the change is a no-op semantically; it keeps both dialects in sync.
+
+ALTER TABLE mate_message ALTER COLUMN content CLOB;
+ALTER TABLE mate_message ALTER COLUMN content_parts CLOB;
+ALTER TABLE mate_skill ALTER COLUMN skill_content CLOB;
diff --git a/mateclaw-server/src/main/resources/db/migration/mysql/V91__widen_message_and_skill_content.sql b/mateclaw-server/src/main/resources/db/migration/mysql/V91__widen_message_and_skill_content.sql
new file mode 100644
index 00000000..5fd212ed
--- /dev/null
+++ b/mateclaw-server/src/main/resources/db/migration/mysql/V91__widen_message_and_skill_content.sql
@@ -0,0 +1,38 @@
+-- V91: Widen mate_message.content / content_parts and mate_skill.skill_content
+-- from TEXT (64KB) to MEDIUMTEXT (16MB).
+--
+-- TEXT caps at 65,535 bytes. A multi-turn ReAct session accumulates tool calls
+-- and observations into content_parts JSON well past that cap, and a long
+-- Chinese final answer (~22k chars × 3 bytes UTF-8) overflows `content`.
+-- The truncation rejects the assistant message INSERT after the SSE stream
+-- has already finished, so users see the reply live but it disappears on
+-- page reload (only the user message survives in the DB).
+--
+-- Idempotent: only modifies the column when its current type is still TEXT.
+
+SET @c := (SELECT DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS
+           WHERE TABLE_SCHEMA = DATABASE()
+             AND TABLE_NAME   = 'mate_message'
+             AND COLUMN_NAME  = 'content');
+SET @s := IF(@c = 'text',
+             'ALTER TABLE mate_message MODIFY COLUMN content MEDIUMTEXT',
+             'SELECT 1');
+PREPARE stmt FROM @s; EXECUTE stmt; DEALLOCATE PREPARE stmt;
+
+SET @c := (SELECT DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS
+           WHERE TABLE_SCHEMA = DATABASE()
+             AND TABLE_NAME   = 'mate_message'
+             AND COLUMN_NAME  = 'content_parts');
+SET @s := IF(@c = 'text',
+             'ALTER TABLE mate_message MODIFY COLUMN content_parts MEDIUMTEXT',
+             'SELECT 1');
+PREPARE stmt FROM @s; EXECUTE stmt; DEALLOCATE PREPARE stmt;
+
+SET @c := (SELECT DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS
+           WHERE TABLE_SCHEMA = DATABASE()
+             AND TABLE_NAME   = 'mate_skill'
+             AND COLUMN_NAME  = 'skill_content');
+SET @s := IF(@c = 'text',
+             'ALTER TABLE mate_skill MODIFY COLUMN skill_content MEDIUMTEXT',
+             'SELECT 1');
+PREPARE stmt FROM @s; EXECUTE stmt; DEALLOCATE PREPARE stmt;