preserve multi-line error formatting in terminal log output

When stderr is a terminal and the log message contains newlines
(e.g. SQL syntax errors with source highlighting and arrows),
print the metadata on the first line and the message below with
its original formatting. Machine output (non-terminal) remains
single-line logfmt.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lovasoa

src/telemetry.rs

@@ -244,9 +244,14 @@ mod logfmt {
                 let _ = write!(buf, " target={target}");
             }
 
-            // 4. msg
-            if let Some(msg) = event_fields.get("message") {
-                write_logfmt_value(&mut buf, "msg", msg);
+            // 4. msg — for terminal, preserve multi-line formatting (e.g. SQL
+            //    error highlighting with arrows); for machine output, flatten.
+            let msg = event_fields.get("message");
+            let multiline_msg = colors && msg.is_some_and(|m| m.contains('\n'));
+            if !multiline_msg {
+                if let Some(msg) = msg {
+                    write_logfmt_value(&mut buf, "msg", msg);
+                }
             }
 
             // 5. Selected span fields in order
@@ -289,6 +294,15 @@ mod logfmt {
 
             buf.push('\n');
 
+            // For multi-line messages on a terminal, print the message below
+            // the metadata line with its original formatting preserved.
+            if multiline_msg {
+                if let Some(msg) = msg {
+                    buf.push_str(msg);
+                    buf.push('\n');
+                }
+            }
+
             // Write atomically to stderr
             let _ = io::Write::write_all(&mut io::stderr().lock(), buf.as_bytes());
         }