Problem

Layer definitions are currently split across frontend and backend with no machine-readable shared contract.

This can cause UI/compiler drift:

• frontend exposes a layer and its params
• backend model generation does not support the same node type or validation rules

Recent bug reports show this mismatch risk in practice.

Why this matters

• Users can build graphs that look valid in UI but fail at compile/train time
• Adding new layers requires touching multiple files with duplicated metadata
• Validation logic becomes inconsistent across frontend and backend

Proposed solution

Introduce a backend-driven layer schema endpoint (single source of truth), e.g.:

GET /api/layers/schema

Each layer schema entry should include:

• type (e.g., customdense, customdropout)
• display metadata (label, category)
• parameter definitions (name, type, required, defaults, min/max/options)
• backend support flag/version (for safe rollout)
• validation constraints and error messages

Frontend should render node config forms and save guards from this schema instead of hardcoded per-layer forms.

Scope

1. Backend:
   • create schema model + endpoint
   • centralize layer metadata in one registry
2. Frontend:
   • consume endpoint
   • render dynamic layer parameter forms
   • use schema-based validation before save/train
3. Compiler:
   • ensure schema-backed node types map to supported build handlers
4. Tests:
   • contract tests for schema shape
   • integration test for at least one layer end-to-end from schema -> UI payload -> compiler

Acceptance criteria

• Backend exposes GET /api/layers/schema with typed param constraints
• Frontend no longer hardcodes layer form logic for core layers
• Save/train validation uses shared schema constraints
• New layer addition requires only registry/schema + compiler handler (no duplicated UI validation logic)
• Tests cover contract consistency between schema and compiler support

Expected impact

• Prevents future UI/backend layer mismatches
• Reduces maintenance overhead when adding new layers
• Improves reliability of visual model-building workflow