fix(coding-agent): use physical temp paths in session-id-readonly test

On macOS tmpdir() is a symlink (/var -> /private/var) while the spawned
CLI's process.cwd() is physical, so session cwd filtering never matched
the fixtures and the fork-target rejection test failed locally.

packages/coding-agent/test/session-id-readonly.test.ts

@@ -1,5 +1,14 @@
 import { spawn } from "node:child_process";
-import { existsSync, mkdirSync, mkdtempSync, readdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import {
+	existsSync,
+	mkdirSync,
+	mkdtempSync,
+	readdirSync,
+	readFileSync,
+	realpathSync,
+	rmSync,
+	writeFileSync,
+} from "node:fs";
 import { tmpdir } from "node:os";
 import { join, resolve } from "node:path";
 import { afterEach, describe, expect, it } from "vitest";
@@ -15,7 +24,10 @@ afterEach(() => {
 });
 
 function createTempDir(): string {
-	const dir = mkdtempSync(join(tmpdir(), "pi-session-id-readonly-"));
+	// realpath: on macOS tmpdir() is a symlink (/var -> /private/var), but the
+	// spawned CLI sees the physical path via process.cwd(). Session cwd
+	// filtering compares paths textually, so the fixture must use physical paths.
+	const dir = realpathSync(mkdtempSync(join(tmpdir(), "pi-session-id-readonly-")));
 	tempDirs.push(dir);
 	return dir;
 }