test(shared): add audit test forbidding direct output.args mutation + fix 9th site

Add replace-tool-args.audit.test.ts that scans src/**/*.ts for direct
output.args property assignments and Object.assign(output.args, ...) outside
the helper. Also fix the 9th mutation site discovered by the audit in
compaction-todo-preserver/hook.ts.

Add replace-tool-args.test.ts with 12 regression tests covering both mutable
and Object.freeze'd output.args scenarios for all hook patterns.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/replace-tool-args.audit.test.ts

@@ -0,0 +1,60 @@
+import { describe, it, expect } from "bun:test"
+import { readdir, readFile } from "node:fs/promises"
+import { join, relative } from "node:path"
+
+const SRC_DIR = join(import.meta.dir, "..")
+
+async function collectTsFiles(dir: string): Promise<string[]> {
+	const results: string[] = []
+	const entries = await readdir(dir, { withFileTypes: true })
+
+	for (const entry of entries) {
+		const fullPath = join(dir, entry.name)
+		if (entry.isDirectory()) {
+			if (entry.name === "node_modules" || entry.name === "dist") continue
+			results.push(...(await collectTsFiles(fullPath)))
+		} else if (entry.name.endsWith(".ts") && !entry.name.endsWith(".test.ts") && !entry.name.endsWith(".audit.test.ts")) {
+			results.push(fullPath)
+		}
+	}
+
+	return results
+}
+
+const HELPER_FILE = "shared/replace-tool-args.ts"
+
+const DIRECT_MUTATION_PATTERN = /output\.args\.\w+\s*=[^=]/g
+const OBJECT_ASSIGN_PATTERN = /Object\.assign\(\s*output\.args/g
+
+describe("replace-tool-args audit", () => {
+	it("#given src/**/*.ts files #when scanning for direct output.args mutation #then no matches found outside the helper", async () => {
+		// given
+		const files = await collectTsFiles(SRC_DIR)
+		const violations: string[] = []
+
+		// when
+		for (const file of files) {
+			const relPath = relative(SRC_DIR, file)
+			if (relPath === HELPER_FILE) continue
+
+			const content = await readFile(file, "utf-8")
+			const lines = content.split("\n")
+
+			for (let i = 0; i < lines.length; i++) {
+				const line = lines[i]
+				if (DIRECT_MUTATION_PATTERN.test(line)) {
+					violations.push(`${relPath}:${i + 1}: ${line.trim()}`)
+				}
+				DIRECT_MUTATION_PATTERN.lastIndex = 0
+
+				if (OBJECT_ASSIGN_PATTERN.test(line)) {
+					violations.push(`${relPath}:${i + 1}: ${line.trim()}`)
+				}
+				OBJECT_ASSIGN_PATTERN.lastIndex = 0
+			}
+		}
+
+		// then
+		expect(violations).toEqual([])
+	})
+})