---
id: LSN-0063
ticket: multi-frontend-validation-boundaries
title: Language vs platform validation ownership
created: 2026-09-19
tags: [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`