Learn Finnish: Tuskin olin kolhaissut hyllyä, kun maljakko putosi. - I had barely bumped the shelf when the vase fell.

This is the standard grammar pattern for a Tuskin ... kun ... (Barely/Hardly ... when ...) narrative sequence. You use the pluperfect (olin kolhaissut) to show that the first action was already completed, and then follow it with kun and the simple past (putosi) for the sudden event that immediately interrupted or followed it.

In English, starting with "Hardly" or "Barely" often flips the word order ("Hardly had I bumped..."). Does Finnish do this with Tuskin?

No, Finnish doesn't use subject-verb inversion here. The word order stays normal. The subject "I" is already built into the -n ending of olin, so the verb comes right after Tuskin, but this is just standard Finnish word order, not a special inversion rule.

The verb is kolhaista (to bump). What does the -aista ending tell us?

The -aista ending makes it a "momentane" verb. These are verbs derived to describe a quick, sudden, or single, fleeting action. It is based on the verb kolhia (to knock around / to dent). So, kolhaista specifically means to give something a single, quick bump.

Why is the shelf (hyllyä) in the partitive case here instead of being a total object?