Improve edit tool diff display with context-aware rendering

- Add generateDiffString() function in edit tool to create unified diffs with line numbers and 4 lines of context
- Store only the formatted diff string in tool result details instead of full file contents
- Update tool-execution renderer to parse and colorize the diff string
- Filter out message_update events from session saving to prevent verbose session files
- Add markdown nested list and table rendering tests

packages/coding-agent/src/main.ts

@@ -337,8 +337,10 @@ export async function main(args: string[]) {
 			sessionManager.saveMessage(event.message);
 		}
 
-		// Log all events
-		sessionManager.saveEvent(event);
+		// Log all events except message_update (too verbose)
+		if (event.type !== "message_update") {
+			sessionManager.saveEvent(event);
+		}
 	});
 
 	// Determine mode: interactive if no messages provided