According to IIA guidance, the internal audit charter gives the internal audit activity the authority to request supporting documentation for the invoices of a third-party service provider. The charter typically outlines the scope, authority, and responsibilities of the internal audit activity, including access to records necessary to carry out its duties.
IIA Standards on the internal audit charter.

The type of risk that an adequately designed and effectively operating system of internal controls should mitigate is "Residual" risk. Residual risk is what remains after internal controls are applied to inherent risk.
This is the primary focus of most internal control systems, which are intended to reduce risks to an acceptable level.
Risk management frameworks and internal control literature, such as COSO and the Institute of Internal Auditors (IIA) guidance.

IIA guidance emphasizes conflict of interest checks in the hiring process for CAEs to ensure the integrity and independence of the internal audit function. Functional reporting to the board or similar oversight is also a standard recommendation but not a hiring precondition.

Intangible assets are indeed categorized as having either a limited life or an indefinite life. Those with a limited life are amortized over their useful life, whereas those with indefinite lives, such as some types of intellectual property, are not amortized but must be tested annually for impairment. This categorization helps in the appropriate financial treatment of intangible assets under accounting standards. References: Financial Accounting Standards Board (FASB) and International Financial Reporting Standards (IFRS) regarding the treatment of intangible assets.

According to IIA guidance, the scope of a consulting engagement is determined by either the engagement supervisor or the chief audit executive (CAE), and it is finalized before beginning fieldwork. This ensures that the objectives, deliverables, and expectations are clearly defined and agreed upon by all parties involved. This clear definition helps guide the consulting engagement, ensuring that it meets the client's needs and aligns with the internal audit activity's capabilities.
The Institute of Internal Auditors (IIA) Standards and Practice Advisories.
IIA's International Professional Practices Framework (IPPF).
"Internal Auditing: Assurance & Advisory Services" by IIA, Chapter on Consulting Services.