Fix write_file compact summary to show actual line/char counts

The write_file compact display was showing 1 line because it was
counting lines in the success message, not the actual written content.

Now parses the tool result (e.g. '✅ wrote 150 lines | 4.2k chars')
to extract and display the correct counts.

Added format_write_file_result() to parse the tool output.

crates/g3-core/src/lib.rs

@@ -2204,9 +2204,9 @@ impl<W: UiWriter> Agent<W> {
                                     match tool_call.tool.as_str() {
                                         "read_file" => Some(streaming::format_read_file_summary(output_len, tool_result.len())),
                                         "write_file" => {
-                                            // Parse the result to get line/char counts
-                                            // Result format: "✅ +N insertions | -M deletions" or similar
-                                            Some(streaming::format_write_file_summary(output_len, tool_result.len()))
+                                            // The tool result already contains the formatted summary
+                                            // Format: "✅ wrote N lines | M chars"
+                                            Some(streaming::format_write_file_result(&tool_result))
                                         }
                                         "str_replace" => {
                                             // Parse insertions/deletions from result

crates/g3-core/src/streaming.rs

@@ -302,6 +302,23 @@ pub fn format_write_file_summary(line_count: usize, char_count: usize) -> String
     format!("✏️  {} lines ({} chars)", line_count, char_display)
 }
 
+/// Format a write_file result for compact display.
+/// Parses the tool result which is in format: "✅ wrote N lines | M chars"
+/// Returns a compact summary like "✏️  N lines (M chars)"
+pub fn format_write_file_result(tool_result: &str) -> String {
+    // Parse "✅ wrote N lines | M chars" or "✅ wrote N lines | M.Mk chars"
+    if let Some(rest) = tool_result.strip_prefix("✅ wrote ") {
+        // rest is "N lines | M chars" or "N lines | M.Mk chars"
+        if let Some((lines_part, chars_part)) = rest.split_once(" | ") {
+            let lines = lines_part.trim_end_matches(" lines");
+            let chars = chars_part.trim_end_matches(" chars");
+            return format!("✏️  {} lines ({} chars)", lines, chars);
+        }
+    }
+    // Fallback: return the original result if parsing fails
+    tool_result.to_string()
+}
+
 /// Format a str_replace result summary.
 pub fn format_str_replace_summary(insertions: i32, deletions: i32) -> String {
     if insertions > 0 && deletions > 0 {