fix(cli): stopped $-pattern expansion when injecting cache prefix

packages/coding-agent/src/cli/bench-cli.ts

@@ -352,7 +352,9 @@ function renderCacheBenchmarkPrefix(prefix: string, namespace: string): string {
 	}
 	// Render the static wrapper first, then inject caller bytes so prompt
 	// normalization cannot trim spaces or collapse blank lines in prefix files.
-	return rendered.replace(CACHE_PREFIX_PLACEHOLDER, prefix);
+	// Function replacer: a prefix containing `$&`/`$'`/`` $` `` must not be
+	// expanded as a string-replacement pattern.
+	return rendered.replace(CACHE_PREFIX_PLACEHOLDER, () => prefix);
 }
 
 async function resolveCachePrefix(

packages/coding-agent/test/bench-cache.test.ts

@@ -494,10 +494,10 @@ describe("bench cache mode", () => {
 		expect(stablePrefixes[0]).not.toContain("\uFFFD");
 	});
 
-	it("preserves significant whitespace from the default prefix-file reader", async () => {
+	it("preserves significant whitespace and replacement patterns from the default prefix-file reader", async () => {
 		const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "omp-bench-cache-prefix-whitespace-"));
 		const prefixPath = path.join(tempDir, "prefix.txt");
-		const exactPrefix = "line one  \n\n\nline two\t\n";
+		const exactPrefix = "line one  \n\n\n$& $' $` $$ line two\t\n";
 		const stablePrefixes: string[] = [];
 		await Bun.write(prefixPath, exactPrefix);
 		try {