fix(coding-agent): dedupe symlinked resources (#3818)

* fix(coding-agent): dedupe symlinked resources

Fixes #3767

* refactor(coding-agent): extract canonicalizePath util for symlink resolution

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

@@ -0,0 +1,84 @@
+import { mkdirSync, mkdtempSync, realpathSync, rmSync, symlinkSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+import { canonicalizePath, isLocalPath } from "../src/utils/paths.js";
+
+let tempDir: string;
+
+afterEach(() => {
+	if (tempDir) {
+		rmSync(tempDir, { recursive: true, force: true });
+		tempDir = "";
+	}
+});
+
+function createTempDir(): string {
+	tempDir = mkdtempSync(join(tmpdir(), "pi-paths-"));
+	return tempDir;
+}
+
+describe("canonicalizePath", () => {
+	it("returns the real path for a regular file", () => {
+		const dir = createTempDir();
+		const file = join(dir, "file.txt");
+		writeFileSync(file, "hello");
+		expect(canonicalizePath(file)).toBe(realpathSync(file));
+	});
+
+	it("resolves symlinks to their targets", () => {
+		const dir = createTempDir();
+		const target = join(dir, "target.txt");
+		const link = join(dir, "link.txt");
+		writeFileSync(target, "hello");
+		symlinkSync(target, link);
+		expect(canonicalizePath(link)).toBe(realpathSync(target));
+	});
+
+	it("resolves directory symlinks", () => {
+		const dir = createTempDir();
+		const targetDir = join(dir, "target-dir");
+		const linkDir = join(dir, "link-dir");
+		mkdirSync(targetDir);
+		symlinkSync(targetDir, linkDir, "dir");
+		expect(canonicalizePath(linkDir)).toBe(realpathSync(targetDir));
+	});
+
+	it("falls back to the raw path when the target does not exist", () => {
+		const dir = createTempDir();
+		const nonexistent = join(dir, "no-such-file");
+		expect(canonicalizePath(nonexistent)).toBe(nonexistent);
+	});
+
+	it("falls back to the raw path for a dangling symlink", () => {
+		const dir = createTempDir();
+		const target = join(dir, "target.txt");
+		const link = join(dir, "link.txt");
+		// Create a symlink whose target does not exist.
+		symlinkSync(target, link);
+		// realpathSync would throw, so canonicalizePath returns the link path.
+		expect(canonicalizePath(link)).toBe(link);
+	});
+});
+
+describe("isLocalPath", () => {
+	it("returns true for bare names", () => {
+		expect(isLocalPath("my-package")).toBe(true);
+	});
+
+	it("returns true for relative paths", () => {
+		expect(isLocalPath("./foo")).toBe(true);
+	});
+
+	it("returns false for npm: protocol", () => {
+		expect(isLocalPath("npm:package")).toBe(false);
+	});
+
+	it("returns false for git: protocol", () => {
+		expect(isLocalPath("git://repo")).toBe(false);
+	});
+
+	it("returns false for https: protocol", () => {
+		expect(isLocalPath("https://example.com")).toBe(false);
+	});
+});