refactor(aws): extract and restructure alias-handling logic to enable safe upcoming fixes

[u-kai]

What does it do?

This PR refactors the alias-handling logic inside adjustEndpointAndNewAaaaIfNeeded and prepares the codebase for upcoming fixes in #5997 and #6017.

To ensure safety and correctness, the refactoring was performed in multiple verifiable stages:

1. Extracted the existing logic
   In commit 7fda240, the original implementation was split into
   oldAdjustEndpointAndNewAaaaIfNeeded and a new adjustEndpointAndNewAaaaIfNeeded,
   with the latter simply delegating to the former.

2. Added comprehensive compatibility tests
   These tests verified that both functions returned identical results for all meaningful input patterns.
   This test suite ensured that extraction did not introduce any behavioral changes.

3. Refactored the new implementation
   In commit b50b0a5, the new function was rewritten for clarity and testability.
   The compatibility tests confirmed the refactored logic remained fully identical to the old version.

4. Removed the old logic and updated tests
   After strict behavioral parity was confirmed, the old function and compatibility tests were removed.
   The test suite was rewritten to validate the intended behavior directly.

This staged process allowed the refactoring to be completed safely while maintaining full functional equivalence throughout the transition.

Motivation

This work originates from the discussion here:
#5997 (comment)

To make future fixes #5997 and #6017 easier and safer to apply, the logic needed to be isolated, simplified, and thoroughly tested.

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

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[ivankatliarchuk]

/ok-to-test

[coveralls]

Pull Request Test Coverage Report for Build 20164321325

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 33 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.04%) to 78.728%

---

Files with Coverage Reduction	New Missed Lines	%
testutils/endpoint.go	6	77.42%
aws/aws.go	27	91.47%

Totals
Change from base Build 20163464704:	0.04%
Covered Lines:	16040
Relevant Lines:	20374

---

💛 - Coveralls

[ivankatliarchuk]

Probably not a big deal, there were some missing lines not covered with tests

before

with the change

[u-kai]

@ivankatliarchuk

Thank you for taking a look.

I don’t think the missing test coverage in the previous tests is a problem, since the behavior between the previous implementation and the refactored one has already been verified to be identical by the comprehensive tests added in commit b50b0a.

The currently untested case is essentially:

if providerSpecificAlias does not exist, nothing happens

if it does exist, it gets removed

In both cases, the final outcome is the same — providerSpecificAlias is absent.
Because of that, my personal view is that adding a dedicated test for this scenario may not be strictly necessary.

That said, if you think it should be covered explicitly, I’m happy to add a test.
What do you think?

[ivankatliarchuk]

/lgtm