Configurable registry service for package-owned runtime invariant checks. The root plugin registers ctx.invariants; it contains no product checks or product-package imports. Every workspace package publishes a ./invariant companion that registers its exact npm package name.

Service: `InvariantService` (`ctx.invariants`)

interface Config {
  enabled?: boolean
  package_allowlist?: string[]
  package_blocklist?: string[]
}

Defaults are enabled: true, package_allowlist: [], and package_blocklist: []. A package is selected only when the service is enabled, the empty allowlist or at least one allowlist pattern matches its full npm name, and no blocklist pattern matches. Blocklist matches therefore override allowlist matches.

Each entry is a case-sensitive JavaScript regular-expression source compiled with new RegExp(pattern). Matching is unanchored unless the source supplies ^ and $; /pattern/flags syntax is not parsed. Blank, whitespace-padded, invalid, or duplicate entries within one list fail service startup. A valid pattern may match no currently loaded package so later loading and HMR remain deterministic.

ctx.invariants.register(packageName, installer) reserves one active registration for the full npm package name, including when filters keep its installer inactive, and returns its disposer. An enabled contribution runs in a dedicated child Cordis fiber. The installer can declare its required service surface through installer.inject and receives fail(message), which throws an InvariantError bound to the registering package. Installer failure disposes the child and releases ownership atomically.

The service owns every registration fiber, while the returned disposer also belongs to the companion fiber. Unloading either side removes the listeners and reservation completely. A companion can therefore reload and register the same package name without retaining trace state or duplicate listeners; packages that need an existing baseline rebuild it during installation.

InvariantError extends Error, carries stable code: 'INVARIANT', and exposes the owning packageName without adding a product-package dependency to the service.

Package companions

An ownership-only generated baseline installs no listeners but still reserves its package name through the real service boundary. A package replaces that marked file when it gains a relational check, retaining the same registration. pnpm run verify-package-invariants checks every package's source registration, export, published files, dependencies, TypeScript reference, and bundle entry.

Four companions currently install stateful checks:

Companion	Registration	Checks
`@deepseek-ai/dsh-session/invariant`	`@deepseek-ai/dsh-session`	sequence, turn/step enclosure, and same-step tool call/result trace
`@deepseek-ai/dsh-agent/invariant`	`@deepseek-ai/dsh-agent`	agent-status transitions
`@deepseek-ai/dsh-scope/invariant`	`@deepseek-ai/dsh-scope`	scoped-event carrier presence and subject consistency
`@deepseek-ai/dsh-agent-loop/invariant`	`@deepseek-ai/dsh-agent-loop`	loop-built model-request reconstruction from the session log

The root entrypoint of each owner remains independent of diagnostics. Loading the service alone installs no checks; loading a companion without the service remains pending on its declared invariants dependency.

Composition

import type { Context } from 'cordis'
import InvariantService from '@deepseek-ai/dsh-invariants'
import * as SessionInvariant from '@deepseek-ai/dsh-session/invariant'

declare const ctx: Context

ctx.plugin(InvariantService, {
  enabled: true,
  package_allowlist: ['^@deepseek-ai/dsh-'],
  package_blocklist: ['^@deepseek-ai/dsh-agent-loop$'],
})
ctx.plugin(SessionInvariant)

The standard agent spine mounts the service and the four stateful companions. Custom compositions choose the companions they want and may disable or filter them without changing package entrypoints. Vitest gives every ordinary root an explicitly enabled service and mounts the current test package's companion; one exhaustive topology mounts all companions once, while focused invariant-service tests construct their own topology to exercise filtering and lifecycle behavior.

Model Experience

None, as the service and companions observe runtime events and requests but never alter prompts, messages, schemas, streams, or tool results.

KV Cache effect

None; invariant checks do not assemble or send provider requests.

Known Limitations and Deferred Work

Stateful checks cover only the four listed package contracts; other companions reserve ownership but add no listeners until their packages gain relational assertions.
Request reconstruction covers frozen loop-built requests with a live session id; direct one-shot calls remain outside that companion's marker contract.
Regular-expression filters are fixed for the service lifetime; changing them requires ordinary Cordis plugin reload.

README.md

dsh-invariants