Fix false positive in isAbsPathOverlapping path boundary check

[soya111]

What this PR does

Fixes a false positive in isAbsPathOverlapping where strings.HasPrefix does not respect path segment boundaries.

For example, /data/tsdb and /data/tsdb-compactor/cache are sibling directories that should not overlap, but strings.HasPrefix("/data/tsdb-compactor/cache", "/data/tsdb") returns true because it operates on raw strings without considering / boundaries.

The fix appends "/" before comparing, so only true parent/child relationships are detected as overlapping.

Which issue(s) this PR fixes or relates to

N/A — discovered while configuring component storage paths.

Checklist

• Tests updated.
• Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• about-versioning.md updated with experimental features.

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Note

Low Risk
Small, well-tested change to config sanity checking that only affects startup validation for filesystem paths and reduces false positives.

Overview
Fixes a config validation bug where filesystem path overlap detection could incorrectly flag sibling directories as overlapping when one path was only a string prefix of the other.

isAbsPathOverlapping now treats / as overlapping with any absolute path and uses a HasPrefix(path, other+"/") boundary check to only detect true parent/child directory relationships; tests were extended with regression cases and the fix is noted in CHANGELOG.md.

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[Copilot]

Pull request overview

Fixes a false positive in isAbsPathOverlapping by making the overlap check respect path segment boundaries (so sibling directories that share a string prefix aren’t treated as overlapping).

Changes:

• Update isAbsPathOverlapping to require a separator boundary when checking parent/child relationships.
• Add regression tests covering “string prefix but not ancestor” cases.
• Add a changelog entry documenting the bugfix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
pkg/mimir/mimir.go	Adjusts overlap detection logic to avoid prefix-based false positives.
pkg/mimir/mimir_test.go	Adds regression test cases for sibling vs ancestor path relationships.
CHANGELOG.md	Records the bugfix in the changelog.

Comments suppressed due to low confidence (1)

pkg/mimir/mimir.go:647

• isAbsPathOverlapping uses filepath.Split/filepath.Abs (OS-specific separators), but the new boundary check hard-codes "/". On Windows paths use \, so this will fail to detect overlaps (false negatives). Consider appending string(filepath.Separator) (or string(os.PathSeparator)) instead of "/" and, if needed, normalize inputs with filepath.Clean to avoid doubled separators.

	// We append "/" to ensure we match on path segment boundaries and avoid false positives
	// like "/data/tsdb" matching "/data/tsdb-compactor/cache".
	return strings.HasPrefix(firstAbsPath, secondAbsPath+"/") || strings.HasPrefix(secondAbsPath, firstAbsPath+"/")

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