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/test/tools.test.ts

@@ -192,7 +192,10 @@ describe("Coding Agent Tools", () => {
 			});
 
 			expect(getTextOutput(result)).toContain("Successfully replaced");
-			expect(result.details).toBeUndefined();
+			expect(result.details).toBeDefined();
+			expect(result.details.diff).toBeDefined();
+			expect(typeof result.details.diff).toBe("string");
+			expect(result.details.diff).toContain("testing");
 		});
 
 		it("should fail if text not found", async () => {