docs: state which error paths arm the connection reset

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qzqmh52NU8fB9RBQNNkJGt

backend/windmill-common/src/db.rs

@@ -368,10 +368,12 @@ pub mod connection_reset {
     }
 
     /// Arms the reset when an error proves a session is stuck in an aborted transaction.
-    /// `Error`'s `From<sqlx::Error>` and `to_anyhow` call this, which covers a query whose
-    /// error is converted or propagated with `?`. A caller that instead inspects the
-    /// `sqlx::Error` in place — formatting it into a message, matching on it — has to call
-    /// this itself, or a poisoned connection reported only there goes unnoticed.
+    /// `Error`'s `From<sqlx::Error>` and `to_anyhow` call this, so it covers `?` into a
+    /// `windmill_common::error::Result` and an explicit `map_err(to_anyhow)`. Everything
+    /// else has to call it: `?` into an `anyhow::Result` goes through anyhow's own `From`,
+    /// and a caller that inspects the `sqlx::Error` in place — formatting it into a
+    /// message, matching on it — never converts it at all. A poisoned connection reported
+    /// only down one of those paths goes unnoticed until something else reports it.
     pub fn note_sqlx_error(err: &sqlx::Error) {
         let sqlx::Error::Database(db_err) = err else {
             return;

backend/windmill-common/tests/connection_reset.rs

@@ -32,8 +32,8 @@ async fn poisoned_connection_is_reset_before_being_handed_out_again(db: Pool<Pos
         err.as_database_error().and_then(|e| e.code()).as_deref(),
         Some("25P02"),
     );
-    // Converting the error is what arms the reset in production, where every `?` on a
-    // sqlx result goes through this same `From`.
+    // Converting the error is what arms the reset in production, for the `?` into a
+    // `windmill_common::error::Result` that most queries use.
     let _ = Error::from(err);
 
     sqlx::query_scalar::<_, i32>("SELECT 1")