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Vox: The AI-Native Programming Language

ADR 038 — AI fixture `@prompt` decorator

ADR 038: AI fixture @prompt decorator

Section titled “ADR 038: AI fixture @prompt decorator”

Status

Section titled “Status”

Accepted (2026-05-11). Implemented via @prompt lowering to chat_with_cascade / ResearchStage in Rust codegen.

Context

Section titled “Context”

Runtime already exposes research-stage cascades (chat_with_cascade, cascade_for_research_stage), but there is no declarative author-time fixture to bind a function to a stage/schema prompt contract.

Decision

Section titled “Decision”

Introduce @prompt(...) decorator on fn declarations with initial payload:

  • stage (Planner | ClaimExtraction | Verification | Synthesis | Judge | SelfVerification)
  • schema (type name for structured contract)
  • optional redact list for sensitive prompt fields

Lowering target is HirAiFixture::Prompt, then Rust codegen calls chat_with_cascade using stage defaults.

Consequences

Section titled “Consequences”
  • Brings runtime stage policy into language-level authoring.
  • Enables structured diagnostics for invalid stage/sensitive prompt shapes.
  • Reuses existing LLM config and cascade machinery rather than introducing parallel prompt engines.

Closed-keyword-table justification

Section titled “Closed-keyword-table justification”

Prompt behavior is represented as a decorator modifier on fn; no new bare prompt block is introduced.

Diagnostic IDs to register

Section titled “Diagnostic IDs to register”
  • vox/prompt/invalid-stage
  • vox/prompt/secret-leakage