How is income tax residency determined for person staying in multiple jurisdictions in a year

Suppose I stayed in multiple countries in a year for significant durations ( say 3 months each in 4 nations) and further assume that double taxation avoidance treaties are in place so how does one determine which jurisdiction one pays taxes in?

For arguments sake say we are considering US, UK or German laws for example.

Is it based on longest stays, or on the source of the income? Or on citizenship?

Furthermore what ensures that the laws of multiple jurisdictions become consistent. I.e you don’t end up having US law determine you are a resident subject to taxation and German law saying the same. In which case the DTA treaty is rendered ineffective.

Details from my Research:

e.g. If I spend 2 months in the US, 2 months in Switzerland and 8 months in Germany this year (and all previous years I spent in the US) then according to the rules below I would be regarded as a tax resident in all three jurisdictions Germany, Switzerland and USA?

How are these things decided then?!

USA rules say:

"You will be considered a United States resident for tax purposes if
you meet the substantial presence test for the calendar year. To meet
this test, you must be physically present in the United States (U.S.)
on at least: 31 days during the current year, and 183 days during the
3-year period…."

German rules say:

"….individuals are deemed to be tax resident if they are physically
present in Germany for more than six months in any one calendar year "

Swiss rules say:

"…For tax purposes, residence may also arise if a person stays in
Switzerland for 30 days,"

Source: https://en.wikipedia.org/wiki/Tax_residence