fix(migrations): make all migrations idempotent; distinguish applied vs error

- 006: ADD COLUMN 补 IF NOT EXISTS
- 002: 5 个索引（status_published/slug_unique/post_tags_post/post_tags_tag/cover）补 IF NOT EXISTS
- migrate.sh: 区分「已应用」与「真出错」，真错误时打印输出并中止，不再静默吞掉（M6）

已验证：第二次运行全部 OK（幂等），不再出现重复对象错误。

migrate.sh

@@ -66,10 +66,20 @@ echo "$MIGRATION_FILES" | sort | while IFS= read -r file; do
     filename=$(basename "$file")
     echo -n "[$filename] ... "
 
-    if psql "$DATABASE_URL" -f "$file" > /dev/null 2>&1; then
+    # 区分「已应用」与「真出错」：迁移本身已幂等（IF NOT EXISTS），正常应返回 0。
+    # 非零退出码视为真错误，打印输出并中止，避免静默吞错（M6）。
+    err_output=$(psql "$DATABASE_URL" -f "$file" 2>&1 >/dev/null)
+    rc=$?
+
+    if [[ $rc -eq 0 ]]; then
         echo "OK"
+    elif echo "$err_output" | grep -qiE "already exists|duplicate|multiple primary keys"; then
+        echo "SKIPPED (already applied)"
     else
-        echo "SKIPPED (already applied or error)"
+        echo "FAIL"
+        echo "$err_output" | head -5 | sed 's/^/  /'
+        echo "Migration aborted due to error in $filename"
+        exit 1
     fi
 done
 

migrations/002_posts.sql

@@ -20,8 +20,8 @@ CREATE TABLE IF NOT EXISTS posts (
     CONSTRAINT posts_status_check CHECK (status IN ('draft', 'published'))
 );
 
-CREATE INDEX idx_posts_status_published ON posts(status, published_at DESC) WHERE deleted_at IS NULL;
-CREATE UNIQUE INDEX idx_posts_slug_unique ON posts(slug) WHERE deleted_at IS NULL;
+CREATE INDEX IF NOT EXISTS idx_posts_status_published ON posts(status, published_at DESC) WHERE deleted_at IS NULL;
+CREATE UNIQUE INDEX IF NOT EXISTS idx_posts_slug_unique ON posts(slug) WHERE deleted_at IS NULL;
 
 CREATE TABLE IF NOT EXISTS tags (
     id   SERIAL PRIMARY KEY,
@@ -34,8 +34,8 @@ CREATE TABLE IF NOT EXISTS post_tags (
     PRIMARY KEY (post_id, tag_id)
 );
 
-CREATE INDEX idx_post_tags_post ON post_tags(post_id);
-CREATE INDEX idx_post_tags_tag ON post_tags(tag_id);
+CREATE INDEX IF NOT EXISTS idx_post_tags_post ON post_tags(post_id);
+CREATE INDEX IF NOT EXISTS idx_post_tags_tag ON post_tags(tag_id);
 
 -- 为封面图添加索引
-CREATE INDEX idx_posts_cover ON posts(cover_image) WHERE cover_image IS NOT NULL;
+CREATE INDEX IF NOT EXISTS idx_posts_cover ON posts(cover_image) WHERE cover_image IS NOT NULL;

migrations/006_add_toc_html.sql

@@ -1 +1 @@
-ALTER TABLE posts ADD COLUMN toc_html TEXT;
+ALTER TABLE posts ADD COLUMN IF NOT EXISTS toc_html TEXT;