fix(db): expand source chain for all DB error logging

The previous fix only covered migration errors. The same truncation
affected two more places, both because tokio_postgres::Error's Display
prints only "db error" while the real message lives in source():

- api/error.rs: AppError::{db_conn,query,tx} logged with {e}, so every
  runtime DB failure showed as "Query failed: db error". The
  constructors' bound is tightened from impl Display+Debug to
  impl std::error::Error so the source chain can be walked; the
  user-facing message stays sanitized (existing tests still pass).
- db/pool.rs: ensure_database formatted tokio_postgres::Error directly
  into the String returned to main.rs' exit(1) path, collapsing to
  "failed to query pg_database: db error" etc.

Adds a shared crate::db::format_with_sources helper (walks source()
with de-dup of placeholder layers) and reuses it from MigrateError's
Display, the AppError constructors, and pool.rs.

src/api/error.rs

@@ -30,21 +30,34 @@ pub enum AppError {
 impl AppError {
     /// 记录并包装数据库连接错误。
     ///
-    /// 日志仅记录 Display 摘要，避免 Debug 输出中的 SQL/参数泄露。
-    pub fn db_conn(e: impl std::fmt::Display + std::fmt::Debug) -> Self {
-        tracing::error!("DB connection failed: {e}");
+    /// 对外只暴露通用提示（脱敏），但服务端日志会展开 source 链，记录完整的
+    /// 失败原因（如 `db error: connection refused`、IO 错误等）。传入的错误类型
+    /// 必须实现 `std::error::Error` —— DB 相关错误（`tokio_postgres::Error`、
+    /// `deadpool_postgres::PoolError`）均满足，这一点是上次"日志只显示 `db error`"
+    /// 问题的根治前提。
+    pub fn db_conn(e: impl std::error::Error) -> Self {
+        tracing::error!(
+            "DB connection failed: {}",
+            crate::db::format_with_sources(&e)
+        );
         AppError::DbConn("connection error".to_string())
     }
 
     /// 记录并包装 SQL 查询错误。
-    pub fn query(e: impl std::fmt::Display + std::fmt::Debug) -> Self {
-        tracing::error!("Query failed: {e}");
+    pub fn query(e: impl std::error::Error) -> Self {
+        tracing::error!(
+            "Query failed: {}",
+            crate::db::format_with_sources(&e)
+        );
         AppError::Query("query error".to_string())
     }
 
     /// 记录并包装数据库事务错误。
-    pub fn tx(e: impl std::fmt::Display + std::fmt::Debug) -> Self {
-        tracing::error!("Transaction failed: {e}");
+    pub fn tx(e: impl std::error::Error) -> Self {
+        tracing::error!(
+            "Transaction failed: {}",
+            crate::db::format_with_sources(&e)
+        );
         AppError::Transaction("transaction error".to_string())
     }
 }
@@ -80,7 +93,10 @@ mod tests {
 
     #[test]
     fn db_conn_hides_internal_details() {
-        let err: ServerFnError = AppError::db_conn("connection refused on port 5432").into();
+        // 入参是实现 Error 的类型；构造函数内部会把 source 链写进日志，
+        // 但对外（ServerFnError）必须只暴露通用提示。
+        let src = std::io::Error::other("connection refused on port 5432");
+        let err: ServerFnError = AppError::db_conn(src).into();
         let msg = err.to_string();
         assert!(
             !msg.contains("5432"),
@@ -94,7 +110,8 @@ mod tests {
 
     #[test]
     fn query_hides_sql_details() {
-        let err: ServerFnError = AppError::query("syntax error at SELECT * FROM").into();
+        let src = std::io::Error::other("syntax error at SELECT * FROM");
+        let err: ServerFnError = AppError::query(src).into();
         let msg = err.to_string();
         assert!(!msg.contains("SELECT"), "should not leak SQL: {msg}");
     }
@@ -124,7 +141,8 @@ mod tests {
     #[test]
     fn transaction_hides_sql_details() {
         // 事务错误同样返回通用提示，不泄露 SQL 细节。
-        let err: ServerFnError = AppError::tx("deadlock detected on UPDATE posts").into();
+        let src = std::io::Error::other("deadlock detected on UPDATE posts");
+        let err: ServerFnError = AppError::tx(src).into();
         let msg = err.to_string();
         assert!(!msg.contains("UPDATE"), "should not leak SQL: {msg}");
         assert!(

src/db/migrate.rs

@@ -91,18 +91,22 @@ impl From<tokio_postgres::Error> for MigrateError {
 
 impl std::fmt::Display for MigrateError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        // 主动展开 source 链：tokio_postgres::Error 的 Display 对 DB 侧错误只打印
+        // 无信息量的 `db error`，真正的 message/SQLSTATE/约束名藏在 source() 里。
         match self {
             MigrateError::Pool(e) => {
-                write!(f, "database pool error: {}", e)?;
-                fmt_source_chain(f, e)
+                write!(f, "database pool error: {}", crate::db::format_with_sources(e))
             }
             MigrateError::Query(e) => {
-                write!(f, "database query error: {}", e)?;
-                fmt_source_chain(f, e)
+                write!(f, "database query error: {}", crate::db::format_with_sources(e))
             }
             MigrateError::Apply { version, source } => {
-                write!(f, "migration {} failed: {}", version, source)?;
-                fmt_source_chain(f, source)
+                write!(
+                    f,
+                    "migration {} failed: {}",
+                    version,
+                    crate::db::format_with_sources(source)
+                )
             }
         }
     }
@@ -118,26 +122,6 @@ impl std::error::Error for MigrateError {
     }
 }
 
-/// 把错误的 `source()` 链逐层拼到 Display 输出里，用 `: ` 分隔。
-///
-/// 存在的原因：`tokio_postgres::Error` 的 `Display` 对 DB 侧错误只会打印
-/// 无信息量的 `db error`，真正的消息文本（如
-/// `column "x" of relation "y" already exists`、SQLSTATE、约束名）藏在
-/// `source()` 链里的 `postgres::error::DbError`。不主动遍历链就会丢失全部上下文，
-/// 日志只显示 `migration 001 failed: db error`，难以定位。
-fn fmt_source_chain(
-    f: &mut std::fmt::Formatter<'_>,
-    mut source: &(dyn std::error::Error + 'static),
-) -> std::fmt::Result {
-    while let Some(next) = source.source() {
-        // `DbError` 的 Display 已经包含 message（必要时还有 detail/hint），
-        // 直接拼上即可；避免逐层重复打印 `db error` 这类占位串。
-        write!(f, ": {next}")?;
-        source = next;
-    }
-    Ok(())
-}
-
 /// 在**已获取**的连接上执行迁移主体逻辑（咨询锁 + 建表 + 应用迁移 + 解锁）。
 ///
 /// 调用方负责自行控制连接获取策略——例如 `main.rs` 启动时用

src/db/mod.rs

@@ -8,6 +8,33 @@
 //! 这种 stub 模式是 Dioxus fullstack 项目的常见做法：服务端函数体在 WASM 构建时会被剥离，
 //! 但模块结构必须保持一致，因此需要一个占位实现来满足编译器的符号解析。
 
+/// 错误格式化工具：把 `std::error::Error` 的 source 链完整展开为字符串。
+///
+/// 存在的原因：`tokio_postgres::Error` 的 `Display` 对 DB 侧错误只会打印
+/// 无信息量的占位串 `db error`，真正的消息文本（如
+/// `column "x" of relation "y" already exists`、SQLSTATE、约束名）藏在
+/// `source()` 链里的 `postgres::error::DbError`。不主动遍历链，日志和错误
+/// 字符串就会全部折叠成 `db error`，无法定位失败原因。
+///
+/// 用法：`format!("...: {}", format_with_sources(&e))` 或直接
+/// `format_with_sources(&e)` 得到完整的 `e: cause: deeper cause`。
+#[cfg(feature = "server")]
+pub fn format_with_sources(e: &dyn std::error::Error) -> String {
+    use std::fmt::Write;
+    let mut s = e.to_string();
+    let mut cur: &dyn std::error::Error = e;
+    while let Some(next) = cur.source() {
+        // 跳过与外层 Display 完全相同的占位层（如 tokio_postgres 的 `db error`），
+        // 避免输出 `db error: db error` 这种重复。只在能带来新信息时追加。
+        let next_disp = next.to_string();
+        if !next_disp.is_empty() && next_disp != s {
+            let _ = write!(s, ": {next_disp}");
+        }
+        cur = next;
+    }
+    s
+}
+
 /// 真实的 PostgreSQL 连接池实现，仅在启用 server feature 时编译。
 #[cfg(feature = "server")]
 pub mod pool;

src/db/pool.rs

@@ -256,12 +256,14 @@ pub async fn ensure_database() -> Result<(), String> {
                 let remaining = deadline.saturating_duration_since(tokio::time::Instant::now());
                 if remaining.is_zero() {
                     return Err(format!(
-                        "could not connect to 'postgres' maintenance database within {timeout_secs}s: {e}"
+                        "could not connect to 'postgres' maintenance database within {timeout_secs}s: {}",
+                        crate::db::format_with_sources(&e)
                     ));
                 }
                 tracing::warn!(
-                    "ensure_database: connect to 'postgres' failed, ~{}s remaining: {e}",
-                    remaining.as_secs()
+                    "ensure_database: connect to 'postgres' failed, ~{}s remaining: {}",
+                    remaining.as_secs(),
+                    crate::db::format_with_sources(&e)
                 );
                 tokio::time::sleep(std::cmp::min(retry_interval, remaining)).await;
             }
@@ -270,7 +272,10 @@ pub async fn ensure_database() -> Result<(), String> {
     // 连接的后台驱动任务：出错时仅记录，连接随即作废。
     tokio::spawn(async move {
         if let Err(e) = connection.await {
-            tracing::warn!("postgres maintenance connection ended: {e}");
+            tracing::warn!(
+                "postgres maintenance connection ended: {}",
+                crate::db::format_with_sources(&e)
+            );
         }
     });
 
@@ -281,7 +286,12 @@ pub async fn ensure_database() -> Result<(), String> {
             &[&db_name],
         )
         .await
-        .map_err(|e| format!("failed to query pg_database: {e}"))?
+        .map_err(|e| {
+            format!(
+                "failed to query pg_database: {}",
+                crate::db::format_with_sources(&e)
+            )
+        })?
         .get(0);
 
     if exists {
@@ -295,7 +305,12 @@ pub async fn ensure_database() -> Result<(), String> {
     client
         .batch_execute(&stmt)
         .await
-        .map_err(|e| format!("failed to create database {db_name:?}: {e}"))?;
+        .map_err(|e| {
+            format!(
+                "failed to create database {db_name:?}: {}",
+                crate::db::format_with_sources(&e)
+            )
+        })?;
     tracing::info!("created database {:?}", db_name);
     Ok(())
 }