Multiple same named stages fall under one E2E assertion

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### Description

Original Author: @dkirillov

If you have multiple stages with the same name, in the E2E test assertions you only need to define as if there's only 1 stage.

In my case, it worked in my favor, because I didn't need to write 5 (times 3) assertions for every deploy stage in the example.

It can, however, be an unpleasant surprise when the user unintentionally names stages the same and only adds one assertion. Or, it can be confusing for the user to know exactly how to add multiple assertions for same named stages what may have different outputs.

I'm not sure if this is something that we thought of and OK'ed, or if this is something we need to think of before anyone runs into it (in a good or bad way).

### Steps to Reproduce

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### Additional Information

No source files, tests, or entry points are named. Start by reproducing the E2E assertion behavior with multiple stages sharing one name and a single assertion, then inspect the relevant assertion handling. Done requires an explicit decision and tests covering whether same-named stages are aggregated or addressed individually.

Written by the indexing model from the issue text.