Fix edit tool failing on Windows due to CRLF line endings

Normalize line endings to LF before matching, restore original style on write.
Files with CRLF now match when LLMs send LF-only oldText.

Fixes #355

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

@@ -1,4 +1,4 @@
-import { mkdirSync, rmSync, writeFileSync } from "fs";
+import { mkdirSync, readFileSync, rmSync, writeFileSync } from "fs";
 import { tmpdir } from "os";
 import { join } from "path";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
@@ -365,3 +365,72 @@ describe("Coding Agent Tools", () => {
 		});
 	});
 });
+
+describe("edit tool CRLF handling", () => {
+	let testDir: string;
+
+	beforeEach(() => {
+		testDir = join(tmpdir(), `coding-agent-crlf-test-${Date.now()}`);
+		mkdirSync(testDir, { recursive: true });
+	});
+
+	afterEach(() => {
+		rmSync(testDir, { recursive: true, force: true });
+	});
+
+	it("should match LF oldText against CRLF file content", async () => {
+		const testFile = join(testDir, "crlf-test.txt");
+
+		writeFileSync(testFile, "line one\r\nline two\r\nline three\r\n");
+
+		const result = await editTool.execute("test-crlf-1", {
+			path: testFile,
+			oldText: "line two\n",
+			newText: "replaced line\n",
+		});
+
+		expect(getTextOutput(result)).toContain("Successfully replaced");
+	});
+
+	it("should preserve CRLF line endings after edit", async () => {
+		const testFile = join(testDir, "crlf-preserve.txt");
+		writeFileSync(testFile, "first\r\nsecond\r\nthird\r\n");
+
+		await editTool.execute("test-crlf-2", {
+			path: testFile,
+			oldText: "second\n",
+			newText: "REPLACED\n",
+		});
+
+		const content = readFileSync(testFile, "utf-8");
+		expect(content).toBe("first\r\nREPLACED\r\nthird\r\n");
+	});
+
+	it("should preserve LF line endings for LF files", async () => {
+		const testFile = join(testDir, "lf-preserve.txt");
+		writeFileSync(testFile, "first\nsecond\nthird\n");
+
+		await editTool.execute("test-lf-1", {
+			path: testFile,
+			oldText: "second\n",
+			newText: "REPLACED\n",
+		});
+
+		const content = readFileSync(testFile, "utf-8");
+		expect(content).toBe("first\nREPLACED\nthird\n");
+	});
+
+	it("should detect duplicates across CRLF/LF variants", async () => {
+		const testFile = join(testDir, "mixed-endings.txt");
+
+		writeFileSync(testFile, "hello\r\nworld\r\n---\r\nhello\nworld\n");
+
+		await expect(
+			editTool.execute("test-crlf-dup", {
+				path: testFile,
+				oldText: "hello\nworld\n",
+				newText: "replaced\n",
+			}),
+		).rejects.toThrow(/Found 2 occurrences/);
+	});
+});