F# code generation Phase B: in-memory saga frames (GH-2969)

[jeremydmiller]

Phase B of the F# code-generation audit (#2969). Teaches the in-memory stateful saga frame set to emit F#, and renders a real saga's start + continue chains to compilable F#.

Stacked on #2971 (which now carries foundation + Phase A). Base is feat-2969-fsharp-codegen-foundation; this rebases onto main once that lands. Diff below is Phase B only.

A string-keyed CountingSaga (Start + Handle) drives the fixture; the driver renders both its chains alongside the Phase A handlers.

Saga frame F# overrides

• CreateNewSagaFrame — let saga = T().
• ResolveSagaFrame / SagaStoreOrDeleteFrame / ConditionalSagaInsertFrame — composites that delegate to their inner frames' F# and render the surrounding if/else (IsCompleted() → delete/update; not-completed → insert).
• SetSagaIdFrame / SetSagaIdFromSagaFrame — SetSagaId + a null-guarded SetTag block (no ?.; pipe SetTag to ignore).
• AssertSagaStateExistsFrame — raise (UnknownSagaException(typeof<T>, sagaId)).
• PullSagaIdFromMessageFrame / PullSagaIdFromEnvelopeFrame — the saga-id resolvers. The string branch uses if isNull x then envelope.SagaId else x; the Guid/numeric branch uses F#'s auto-tupled match Type.TryParse(s) with | true, v -> … | _ -> …, with Unchecked.defaultof<T> as the zero/default sentinel.

In-memory Load/Store/Delete are plain MethodCalls (already emit F#); the not-found null-guard comes from JasperFx's IfElseNullGuardFrame (already F#).

Generated F# (excerpt — the saga continue chain)

let incrementCount = context.Envelope.Message :?> IncrementCount
let sagaId = if isNull incrementCount.Id then context.Envelope.SagaId else incrementCount.Id
if System.String.IsNullOrEmpty(sagaId) then
    raise (IndeterminateSagaStateIdException(context.Envelope))
let countingSaga = _inMemorySagaPersistor.Load<CountingSaga>(sagaId)
if isNull countingSaga then
    raise (UnknownSagaException(typeof<CountingSaga>, sagaId))
else
    context.SetSagaId(sagaId)
    countingSaga.Handle(incrementCount)
    if countingSaga.IsCompleted() then
        _inMemorySagaPersistor.Delete<CountingSaga>(sagaId)
    else
        _inMemorySagaPersistor.Store<CountingSaga>(countingSaga)

Verification

• Compile-gate test — the regenerated Generated.fs (4 handler chains + 2 saga chains) compiles via dotnet build.
• fsharp-coverage — 24 implemented / 2 skipped / 18 remaining of 44 (up from 15/2/27 at Phase A).
• dotnet build wolverine_fsharp.slnx -c Release — clean.
• Full dotnet build wolverine.slnx -c Release regression — 0 warnings, 0 errors.

Deferred (not reachable from a minimal in-memory saga, so not exercised here)

• CreateMissingSagaFrame (reassigns the loaded-saga var → needs the load Variable marked Mutable so F# renders let mutable; only used for start-or-continue / NotFound).
• Store-specific operation wrappers LoadSagaOperation / SagaOperation / EnrollAndFetchSagaStorageFrame<,>.
• ShouldProceedGuardFrame (ResequencerSaga).
• The Marten/Polecat data-requirement frames (ThrowRequiredDataMissingExceptionFrame, ConstructSpecificationFrame, …) — separate assemblies; need per-store fixture projects (the issue's open per-store-granularity question).
• The behavioural run-step (TypeLoadMode.Static + InvokeAsync + assert) — Phase B stays at compile-gate depth for now, like Phase A.

Part of #2969.

🤖 Generated with Claude Code