fix(coding-agent): correct bash truncation line count

closes #4818

packages/coding-agent/test/tools.test.ts

@@ -580,6 +580,28 @@ describe("Coding Agent Tools", () => {
 			expect(getTextOutput(result)).toContain("line 4999");
 		});
 
+		it("should not count a trailing newline as an extra truncated bash output line", async () => {
+			const operations: BashOperations = {
+				exec: async (_command, _cwd, { onData }) => {
+					for (let i = 1; i <= 4000; i++) {
+						onData(Buffer.from(`line-${String(i).padStart(4, "0")}\n`, "utf-8"));
+					}
+					return { exitCode: 0 };
+				},
+			};
+			const bash = createBashTool(testDir, { operations });
+
+			const result = await bash.execute("test-call-trailing-newline-line-count", { command: "many-lines" });
+			const output = getTextOutput(result);
+
+			expect(result.details?.truncation?.totalLines).toBe(4000);
+			expect(result.details?.truncation?.outputLines).toBe(2000);
+			expect(output).toContain("line-2001");
+			expect(output).toContain("line-4000");
+			expect(output).toMatch(/\[Showing lines 2001-4000 of 4000\. Full output: /);
+			expect(output).not.toContain("4001");
+		});
+
 		it("should decode UTF-8 characters split across output chunks", async () => {
 			const euro = Buffer.from("€\n", "utf-8");
 			const operations: BashOperations = {