[TS Calls][P0] Finish simplifying the model contract before further integration

[CaelmBleidd]

Part of #360. Priority: P0 / Urgent.

Goal

Finish the agreed simplification in the existing #365/#366 work before building further model integration on the old configuration layers.

Scope

• Reuse the work already in PR [TS Calls] Add guarded semantic models with a simplified contract #377 and PR [TS Calls] Execute semantic models written in TypeScript #380. This issue is a completion gate, not a request to implement the same changes on another branch.
• Keep one model object with a stable ID, a declarative call target, and execution returning guarded successors plus an optional residual domain. Keep normal/exceptional completion and deferred state changes.
• Keep one immutable enabled-model catalog and one residual fallback setting. An empty enabled set disables model lookup; experimental combinations are run configurations.
• Remove separate descriptor/registration/backend/implementation wrappers, repeated implementation-kind tags, supported-domain IDs, and stored precision/outcome values derivable from the execution or decision.
• Execute source models through the normal EtsIR interpreter. Use Kotlin intrinsics for engine primitives such as symbolic memory copying; use Array.shift with memcpy as the intrinsic example and Array.pop as the source-model example.
• Preserve proof of the actual built-in target and receiver representation. A method name or the first possible type is not proof. Unknown/fake receivers without sufficient evidence use fallback.
• Keep guard disjointness, completeness, aliasing and exception behavior as model obligations covered by focused tests. Do not issue an additional solver query on every call merely to validate a trusted built-in model.
• Preserve one observer decision per application and a separate residual decision. Observation must not change exploration.
• Preserve deterministic selection and enabled-set identity. Record tool revision and external model content identity in experiment metadata; do not add manually maintained model versions or compatibility negotiation.

Completion gate

• The common model contract and intrinsic integration in PR [TS Calls] Add guarded semantic models with a simplified contract #377 use the simplified configuration; obsolete infrastructure is removed from that layer and its documentation.
• Focused contract/intrinsic tests protect guards, normal/exceptional completion, mutation/aliases, unknown receivers and fallback; the normal usvm-ts checks pass.
• Existing source-model work in PR [TS Calls] Execute semantic models written in TypeScript #380 has a concrete migration path to the simplified interface. Completing the source models or all [TS Calls] Execute semantic models written in TypeScript #366 acceptance tests is not a prerequisite for closing this gate.
• The simplification is reviewed and delivered through the existing PR [TS Calls] Add guarded semantic models with a simplified contract #377, possibly together with [TS Calls] Register and execute guarded semantic models #365. This issue does not require a third implementation PR. Source-model completion remains downstream in [TS Calls] Execute semantic models written in TypeScript #366.
• [TS Calls] Register and execute guarded semantic models #365 and [TS Calls] Execute semantic models written in TypeScript #366 cannot be considered complete until this gate is satisfied. Later catalog expansion and final evaluation use this simplified contract.

No general plugin framework, dynamic model loading, full ECMAScript library, or unrelated core redesign is required.