Fix nondeterministic private field ordering in Lifter

[LPTK]

The private fields generated by the lifter had nondeterministic ordering because they were built by iterating over Map values derived from Set operations. Scala's Set and Map do not guarantee stable iteration order.

The fix uses sorted ordered lists (passedSymsOrdered, capturesOrdered, passedDefnsOrdered, and new liftedObjsOrdered) to look up map values in a deterministic order based on symbol UIDs, instead of iterating map values directly.

Agent-Logs-Url: https://github.com/LPTK/mlscript/sessions/07ac81ed-dfff-467c-af13-4a25818d2faa

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Original PR comment by Copilot:

Private field order in generated code was nondeterministic across runs, caused by iterating Scala Map.values / Set elements which have no guaranteed iteration order. This manifested as "bump test" commits that only reordered fields like x¹ and y² swapping.

Changes

• LiftedClass.extraPrivSyms: Replaced Map.values concatenation with lookups through the already-sorted passedDefnsOrdered, capturesOrdered, passedSymsOrdered lists — matching the ordering convention used by auxParams and formatArgs

// Before: nondeterministic Map.values iteration
private val extraPrivSyms = 
  liftedObjsSyms.values ++ passedSymsMap_.values.map(_.ts)
  ++ capSymsMap_.values.map(_.ts) ++ defnSymsMap_.values.map(_.ts)

// After: deterministic uid-sorted lookups
private lazy val extraPrivSyms: List[TermSymbol] = 
  liftedObjsOrdered.map(liftedObjsSyms)
  ::: passedDefnsOrdered.map(defnSymsMap_(_).ts)
  ::: capturesOrdered.map(capSymsMap_(_).ts)
  ::: passedSymsOrdered.map(passedSymsMap_(_).ts)

• RewrittenClass / RewrittenCompanion: Replaced liftedObjsSyms.values.toList with liftedObjsOrdered.map(liftedObjsSyms) in privateFields construction
• GenericRewrittenScope / ClsLikeRewrittenScope: Added liftedObjsOrdered: List[InnerSymbol] sorted by uid, paralleling the existing passedSymsOrdered / capturesOrdered / passedDefnsOrdered pattern

[Copilot]

Pull request overview

This PR addresses nondeterministic ordering of generated private fields in the lifter by avoiding iteration over Set/Map.values (which have no guaranteed stable order) and instead indexing map entries via UID-sorted key lists. This reduces “no-op” diffs in generated output caused by field reordering.

Changes:

• Introduce liftedObjsOrdered (UID-sorted) and use it instead of liftedObjsSyms.values.toList when emitting privateFields for rewritten classes/companions.
• Make LiftedClass.extraPrivSyms deterministic by building it via the already-ordered key lists (passedDefnsOrdered, capturesOrdered, passedSymsOrdered) instead of Map.values.
• Update the golden lifter output test to reflect the new stable field order.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
hkmc2/shared/src/main/scala/hkmc2/codegen/Lifter.scala	Reworks private-field list construction to use UID-sorted keys rather than Map.values iteration.
hkmc2/shared/src/test/mlscript/lifter/ClassInFun.mls	Updates expected output ordering for private fields in a lifter snapshot test.

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[LPTK]

Argh, closed because I mistakenly deleted the source branch...

[LPTK]

@CAG2Mark Copilot has annoying restrictions on cross repo PRs, so the PR continues there: LPTK#18

[CAG2Mark]

LGTM, but I have comments on the other PR

Also see the above comment by Copilot, which is valid.

[CAG2Mark]

Pls merge this first and then it will be good to go: https://github.com/CAG2Mark/mlscript/commits/fix-ordering-2/