vcsdd-verification-architecture

name	vcsdd-verification-architecture
description	Use this skill when writing Phase 1b verification architecture documents. Provides purity boundary mapping, proof obligation design, and tier assignment guidance.
origin	VCSDD

VCSDD Verification Architecture

When to Activate

• Phase 1b (verification architecture)
• Designing proof obligations for a feature
• Reviewing purity boundaries

Purity Boundary Design

Identifying the Pure Core

A function belongs in the pure core if:

• Same input ALWAYS produces same output (no randomness, no time, no state)
• No I/O operations (no file reads, network calls, DB queries)
• No mutations to shared state
• Can be tested without mocks

Identifying the Effectful Shell

A function belongs in the effectful shell if:

• It reads from external sources (files, DB, APIs)
• It writes to external sinks
• It uses system time or randomness
• It coordinates side effects

Architecture Pattern

+---------------------------------+
|         Effectful Shell         |
|  (HTTP handlers, DB adapters)   |
|                                 |
|    +---------------------+      |
|    |     Pure Core       |      |
|    |  (business rules,   |      |
|    |   parsing, calcs)   |      |
|    +---------------------+      |
+---------------------------------+

Proof Obligation Design

Each proof obligation should specify:

• What property is being proved
• Which verification tier is appropriate
• Whether it is required for Phase 6 convergence

Good proof obligations:

• PROP-001: Parse(Serialize(x)) == x (round-trip property)
• PROP-002: Validate(x) == false implies Transform(x) raises an error
• PROP-003: Token budget never goes negative

Poor proof obligations (too vague):

• PROP-004: Code is correct
• PROP-005: No errors occur