Validate hiring request under role constraints

## Problem You are building a simple HR assignment validator for a platform with **companies**, **employees**, and **job roles**. When the system receives a request to assign an employee to a role in a company, it must enforce the following rules: 1. **Role capacity per company:** In a given company, **each role** can be held by **at most 5 employees** at the same time. 2. **Max roles per employee per company:** An employee can hold **at most 2 roles in the same company** at the same time. If a request violates any rule, the system must return `invalid` and also provide a **reason**. Otherwise, it should apply the assignment and return `valid`. ## Input - An initial set of existing assignments. - A sequence of `add` requests, each of the form: - `employee_id`, `company_id`, `role_name` ## Output For each `add` request, output either: - `valid` (and the assignment is applied), or - `invalid: <reason>` where `<reason>` clearly states which rule was violated. ## Notes / Clarifications - If an employee is already assigned to the same role in the same company, treat it as `valid` (no-op), unless you choose to define it as an error—state your assumption. - If both rules would be violated, you may return either a single reason or multiple reasons, but be consistent. ## Constraints (you may assume) - Up to `10^5` total assignments and requests. - IDs/role names are strings. ## Example (illustrative) Given existing assignments where role `SWE` at company `C1` already has 5 employees, adding another `SWE` to `C1` should return: - `invalid: role capacity exceeded (max 5 per role per company)`