How do you optimise a low-level vault-buster heist character?

I’m going to run a campaign that starts with characters on level one and finishes on reaching level six in 998 YK. I’m looking for a complete path for the character build through level one to six. One of my players wants to play an expert at busting open magically secured and conventionally re-enforced vaults in nobility-estates from various nobles who have access to a caster with up to third level spells – either a cleric, wizard or sorcerer. At one point or another, the character will encounter each variant of the spellcasters. This PCs role is as part of a team:

Somebody else deals with getting in and out
Somebody else deals with information and resources gathering
Somebody else deals with organising combat should it occur

The group wants to avoid fighting most of the time.

The group is most likely to solve encounters via roleplaying in a conniving way. If the character additionally provides magical disguises, then that would be desirable, but it isn’t necessary.

What is that optimal build that can deal with magical defences that may occur during various heists on these estates?

Consider the following restrictions:

  • Only official material, Unearthed Arcana is not legal for this character creation. The choice is limited to core rules, ERftLW and one other source.

  • All PHB and ERftLW races are legal. The choice of Subraces depends on the selection of sources.

  • Starting attributes are achieved by the point-buy or standard array.

  • Consistency is imperative: a build that only functions under unreliable circumstances or relies on later levels to function is undesirable.