[TS Calls] Audit and classify existing semantic approximations

[CaelmBleidd]

Part of #360. Reuses #361 and feeds #367/#385.

Goal

Review existing production and historical approximations once, deciding what is sound to retain, migrate or reject.

Scope

• Start from [TS Calls] Establish a clean integration baseline #361's production inventory and recovered archive. Add historical candidates, including the old 29-model registry, without redoing the same inventory from scratch.
• For each item record its origin, semantic operation, proven target/receiver assumptions, supported/residual domain, effects/exceptions/aliases, tests and frontend assumptions.
• Distinguish mandatory language semantics and engine/frontend correctness fixes from optional library-model choices.
• Classify optional models as source-model migration, genuine engine intrinsic, rewrite, reject or deferred pending evidence.
• Prefer ordinary TypeScript for expressible library semantics. Choose an intrinsic only for a justified symbolic engine operation.
• Carry accepted candidates into [TS Calls] Build a real-project call census and model roadmap #367's roadmap, but do not automatically require migration of every historical model.
• Keep mandatory semantics and correctness fixes identical across [TS Calls] Evaluate fallback policies and models with concrete replay #385 profiles; they are not experimental model toggles.

Definition of Done

• Every inventoried item has a reasoned disposition; blocked cases have a concrete reason.
• Accepted candidates have a domain, intended implementation mechanism and current validation status.
• A small evaluation subset can be selected without merging the historical branch.
• Missing selected-family implementations get bounded follow-up issues that block [TS Calls] Evaluate fallback policies and models with concrete replay #385.
• Inventory/audit work does not wait for unrelated model infrastructure.

This is a reviewed inventory, not implementation of the whole standard library or another registry framework.