prometeu-studio/discussion/lessons/DSC-0060-multi-frontend-validation-boundaries/LSN-0063-language-vs-platform-validation-ownership.md

id	ticket	title	created	tags
LSN-0063	multi-frontend-validation-boundaries	Language vs platform validation ownership	2026-09-19	compiler compiler-general compiler-pbs backend validation multi-frontend

Language vs platform validation ownership

Original Problem

PBS mixed two kinds of rejection. Some failures only make sense with the language: syntax, types, markers, barrel files, imports. Others belong to any executable frontend: malformed IRBackend, invalid lifecycle declarations, missing assembled wrappers, host-capability identity, bytecode/preload.

Without an ownership rule, the next frontend would copy PBS validators, or the common layer would start knowing [Init], barrel, and E_SEM_*. Spec 19 was still titled as PBS verification, and the PBS diagnostics catalog listed wrapper and boot-guard failures as PBS coverage.

Lifecycle assembly had already moved (LSN-0062). That proved the pattern. It did not inventory the rest.

Consolidated Decision

A validation lives at the lowest layer that understands the failure without knowing the source language.

• Language: needs AST, tokens, a language marker, a barrel, or another source rule.
• Platform: can be checked on IRBackend, IRLifecycleDeclaration, IRVM, PBX, host/capability tables, or ids.

The discussion published that matrix. It did not extract a generic validator-core and did not move validators whose common contract is not closed.

Host admission is split. PBS owns the source shape of [Host] and [Capability]. Platform owns canonical (module, name, version) identity and capability consistency once those facts exist on IRReservedMetadata. The current validator may stay in the PBS package until a later plan. E_HOST_* is not eternal PBS semantics.

The same fact may exist on both sides with distinct identities. PBS can report E_SEM_MISSING_PROJECT_FRAME; the common layer still rejects an executable declaration with no frame root.

Platform codes are COMMON_*, LOWER_IRVM_*, or MARSHAL_*. PBS keeps E_PARSE_*, E_SEM_*, E_LINK_*, and E_HOST_*. Copy origin/span when present; a missing origin is a structural error, not a reason to invent a span.

Linking and barrel stay language-owned. Addressable is platform-owned and was classified only. SDK canonical source and the broad architectural harness stay on adjacent discussions.

Final Implementation

The work was editorial and test-facing.

Spec 19 is now Compiler Verification and Safety Checks Specification. Gates S-U and S-I are unchanged. Section 11 states the classification rule, the English ownership matrix, diagnostic identity, dual reporting, and the host-admission split. It explicitly refuses validator-core extraction and package moves.

PBS diagnostics spec 12 keeps marker, syntax, semantics, linking, and host-attribute coverage. Common structural failures now point at spec 19 section 11 and spec 20 instead of appearing as PBS required coverage.

Spec 20 cross-references that same compiler-general ownership. The conformance matrix added G19-11.1 through G19-11.6 and PBS12-11. CommonBackendArchitectureTest now guards backend/, lifecycle/, and all common pipeline stages. ValidationOwnershipSpecTest locks the title, matrix, and PBS recut.

PbsHostAdmissionValidator remains under p.studio.compiler.pbs. No linking or asset production code moved.

Examples

Language-owned:

• parse errors;
• [Init] / [Frame] signature and colocation;
• barrel and import failures;
• host call not allowed during init.

Platform-owned and already implemented:

• invalid IRLifecycleDeclaration;
• assembled wrapper, boot guard, and synthetic origin preconditions;
• IRVM and marshal rejection families.

Classified as platform, not moved:

• canonical host-binding identity on IRReservedMetadata;
• Addressable / asset path.

Dual reporting:

• missing [Frame] in PBS source is E_SEM_MISSING_PROJECT_FRAME;
• an executable declaration without frame root is a common structural error.

Pitfalls

• Do not treat “classified as platform” as “move the class now.” Host admission still waits on the SDK source discussion.
• Do not merge language and platform failures into one hybrid code. Two identities are cheaper than a lost message.
• Do not put PBS governance or PBS diagnostics in charge of compiler-general safety gates.
• Do not scan PBS frontend sources with the platform architecture guard. The guard is for common validators, not for the language package that must remain.
• Do not invent a validator-core because several common checks exist. They already live on their stages.

References

• Decision: DEC-0047
• Plan: PLN-0126
• Related lesson: LSN-0062 - Common lifecycle assembly after frontend declaration
• Related lesson: LSN-0059 - Common IRBackend handoff and backend guardrails
• docs/specs/compiler/19. Verification and Safety Checks Specification.md
• docs/specs/compiler-languages/pbs/12. Diagnostics Specification.md
• docs/specs/compiler/20. IRBackend to IRVM Lowering Specification.md
• docs/specs/compiler/22. Backend Spec-to-Test Conformance Matrix.md
• prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/specs/ValidationOwnershipSpecTest.java
• prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/specs/CommonBackendArchitectureTest.java