A forward, soft-typing-style pass (simplified HM: monovariant, never-fails,
lattice top = :any) in jolt.passes, run after the inline/scalar-replace
fixpoint when the optimization mode is on. It types expressions from literals
and arithmetic, flows the type through let bindings, and joins at if-branches.
Where a keyword-lookup subject is PROVEN to be a plain struct map it sets
:hint :struct (the same channel a manual hint uses, so the back end drops the
:jolt/type guard); where the type is :any it leaves the dynamic guard in place.
Sound by construction: a concrete type is assigned only when proven (scalar
keys with non-nil/non-false values for a struct-map), so a wrong bare get can't
happen. This is the foundation; on its own it mostly overlaps Route 1
scalar-replacement (which already eliminates non-escaping let-bound maps), so
its standalone win is small. Phase 1 (inter-procedural) is where escaping
params get typed.
Verified: conformance 335/335 x3, full jpm test; new type-infer-test pins the
flow rules and the sound :any fallback (cases force the map to escape so the
test isolates inference from scalar-replacement).
