Tianyi Cui
11a29fdefe
New @deepseek-ai/dsh-invariants plugin (pure listeners, off in prod) asserts the event taxonomy at runtime — seq monotonicity, turn/step nesting, a tool/result needs a prior tool/call (NOT the converse), legal agent/status transitions — and deep-freezes logged event data so mutating history throws. Seeded sessions are checked + frozen on session/created. The real RFC 008 fix is always-on: deriveMessages now structured-clones the content it emits, so the loop's sanctioned request/adapter mutation can no longer reach back and rewrite the append-only log. The pervasive DeepReadonly<T> type flip is rejected (compile-only, high-noise, castable) — recorded in ADR 0012, which folds in RFC 008. Wired into both demos.
26 lines
2.4 KiB
Markdown
26 lines
2.4 KiB
Markdown
# RFC 005: Runtime validation at the model boundary, error taxonomy, dev-mode invariants
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Status: partially implemented — part 1 (arg validation) → [ADR 0011](../adr/0011-runtime-arg-validation.md); part 3 (dev invariants) → [ADR 0012](../adr/0012-dev-invariants-over-deep-readonly.md); part 2 (error taxonomy) in progress
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## Problem
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Three gaps where compile-time guarantees stop:
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1. Tool args are model-generated JSON — `defineTool`'s `InferArgs<S>` claim is only as true as the model's output. Today a malformed call reaches `execute` untyped-in-practice.
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2. Tool errors flatten to a text block; name/code/stack are lost, so future sandbox/retry plugins can't distinguish ENOENT from EACCES, and the model gets less actionable feedback than it could.
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3. Loop ordering invariants (seq monotonicity, step/turn event nesting, turn-number continuity) are asserted only where tests look.
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## Proposal
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1. **Schema validation in defineTool**: before `execute`, validate parsed args against the SchemaSpec (the converter already encodes the structure — a small interpreter walks it: presence of required keys, primitive type checks, enum membership, recursion into objects/arrays). On mismatch, return an `isError` ToolExecutionResult describing the violation — the model can self-correct. Raw-registered tools (MCP) keep validating their own input.
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2. **Structured error taxonomy**: per-package error classes extending a common `HarnessError` (name, `code`, `cause` chaining). `ToolExecutionResult` gains optional `error: { name, code }` alongside the model-facing text. The loop's `errorData` consumes it; session `error` events carry the code. This also properly fixes the non-Error-throw message degradation found in review.
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3. **Dev-mode invariants**: a `dsh-invariants` debug plugin (everything is a plugin — it's just listeners) asserting, when enabled: session seq strictly increases; `step/start` precedes its chunks; `turn/start`/`turn/end` pair and nest; tool/call has a matching tool/result; status transitions are legal. Enabled in tests and the demo; off in production. Doubles as executable documentation of the event contract.
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## Plan
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2 first (taxonomy is a dependency of 1's error shape), then 1, then 3. Property tests (RFC 001) then close the loop: generated args ↔ validator ↔ InferArgs agreement.
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## Risks
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Validator/InferArgs drift — covered by the RFC 001 composition property. Validation cost per call is negligible next to a model call.
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