Term for the property of having a formal and transparent track record

The answers already given are good in everyday English, but in the specific technical context you're describing, I would describe this as an audit trail (discussion of the term on Wikipedia). "We require an audit trail for all changes" conveys exactly the meaning you want.

[Maybe slightly off-topic here, but do you actually need to find a phrase for this at all - why not just say that "all code must be held under version control"? It's a very standard requirement, and surely the people reading your proposal will understand what it means and why.]

From your description I think the term traceability might fit in the context:

• the ability to verify the history, location, or application of an item by means of documented recorded identification.

• Other common definitions include the capability (and implementation) of keeping track of a given set or type of information to a given degree, or the ability to chronologically interrelate uniquely identifiable entities in a way that is verifiable.

(Wikipedia)

also validation

• the process to establish the soundness, accuracy, or legitimacy of something.

We require TERM for all changes done to the source code.
We require this process to have TERM.
We require this process to be TERM.

the only word with which you would replace TERM is "audit trail" as Morton explains.

This is commonplace in software development in English.

PS- I suppose literally "an audit trail". In the third example above: don't use that form. You'd use the second form.

I think what you're looking for is transparency. While most of the definitions I find online focus on the literal sense in which a window is transparent, the word is commonly used for processes. For example, the Business English Dictionary defines it as:

a situation in which business and financial activities are done in an open way without secrets, so that people can trust that they are fair and honest

This meaning is also mentioned in definition 4b and c of the Online Free Dictionary for transparent:

4.

a. Easily seen through or detected; obvious: transparent lies.

b. Free from guile; candid or open: transparent sincerity.

c. Open to public scrutiny; not hidden or proprietary: transparent financial records.