fix(agent-script): prevent Object globals from mutating host prototypes

[kamilio]

Motivation

• Prevent sandboxed scripts from reaching and mutating host prototypes (for example Object.prototype) via the newly exposed Object.assign/Object.freeze globals, which cross the sandbox boundary and enable prototype pollution or process-wide DoS.

Description

• Route the Object.freeze global through a guarded helper freezeSandboxValue so freezing is only applied to approved sandbox-owned targets and is a no-op for other values.
• Tighten target validation with isAssignableSandboxTarget so only arrays or plain objects whose prototype is Object.prototype (and that are not sandbox closures/promises) are considered assignable.
• Keep Object.assign semantics but reject non-assignable targets with a TypeError to prevent writes to host prototype objects.
• Add a regression test that asserts Object.assign(Object.prototype, ...) is rejected and Object.freeze(Object.prototype) is a no-op that does not freeze the host prototype.

Testing

• Ran npm run test:unit -- packages/agent-script/src/interp/globals/object-array.test.ts and all tests passed (5 passed).
• Pre-commit checks (npm run lint:eslint and tsc -p tsconfig.build.json --noEmit) ran as part of the commit hook; lint produced warnings only and type check passed.

---

Codex Task

[poe-code-agent]

Requested changes: Object.assign/freeze now rejects sandbox object literals.

[poe-code-agent]

Object literals are created with Object.create(null) in interpreter.ts, so this now rejects ordinary script code like Object.assign({}, { ok: true }) and Object.freeze({}). I verified run('return Object.assign({}, { ok: true }).ok') now throws this TypeError. Please allow sandbox null-prototype objects while still blocking the host prototypes.

Suggested change

	if (Array.isArray(value)) {
	return true;
	}
	return Object.getPrototypeOf(value) === Object.prototype;
	if (Array.isArray(value)) {
	return value !== Array.prototype;
	}
	const prototype = Object.getPrototypeOf(value);
	return prototype === Object.prototype || (prototype === null && value !== Object.prototype);

[poe-code-agent]

Please add coverage for the sandbox object-literal/null-prototype path here too. The current test covers Object.prototype, but not {} from the interpreter, which is the regression path for Object.assign({}, source) and Object.freeze({}).