Fix non-transitive rule precedence for routes without hostnames

[sergeylanzman]

Issue

Related to #4807 and #4792.

Description

getHostnameListPrecedenceOrder compares two hostname lists positionally, but only up to min(len(a), len(b)):

length := min(len(hostnameListOne), len(hostnameListTwo))
for i := range length {
    precedence := getHostnamePrecedenceOrder(hostnameListOne[i], hostnameListTwo[i])
    if precedence != 0 {
        return precedence
    }
}
return 0

When a route has no hostnames (a catch-all /* HTTPRoute), its list is empty, so min(0, N) = 0, the loop never executes, and the function returns 0 ("equal") instead of treating the empty list as the least specific.

Why this is a problem: a catch-all becomes hostname-equal to every route, so its precedence falls through to path length / creation timestamp. Meanwhile host-specific routes are ordered against each other by hostname specificity (path is never consulted). Mixing these two criteria makes compareHttpRulePrecedence non-transitive — it contains comparison cycles, e.g.:

catch-all  >  console  (equal path -> older creation timestamp wins)
console    >  login    (more specific hostname wins, path ignored)
login      >  catch-all (longer path wins)

sort.Slice requires the less function to be a strict weak ordering; given a non-transitive comparator its output is undefined and depends on the input order (which varies between reconciles). In practice this let the catch-all rule intermittently sort above host-specific rules, so requests that should match host-scoped rules were served by the catch-all.

Fix: after all compared hostnames tie, break by hostname-list length — a shorter (in the extreme, empty) list constrains fewer hostnames and is therefore less specific, so it gets lower precedence. This makes an empty hostname list always lose to any route that has hostnames and restores a strict weak ordering, so the sort result no longer depends on input order.

The same getHostnameListPrecedenceOrder is used by both compareHttpRulePrecedence and compareGrpcRulePrecedence, so the fix covers HTTP and GRPC routes.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[kubernetes-prow]

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[kubernetes-prow]

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.36%. Comparing base (82c3870) to head (0e2f60b).
⚠️ Report is 30 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4809      +/-   ##
==========================================
+ Coverage   57.08%   57.36%   +0.27%     
==========================================
  Files         396      396              
  Lines       31572    31553      -19     
==========================================
+ Hits        18022    18099      +77     
+ Misses      12492    12393      -99     
- Partials     1058     1061       +3     

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[zac-nixon]

/lgtm
/approved

thanks for the fix!

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sergeylanzman, shraddhabang

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