npm package: @sisu-ai/mw-invariants
Description: Detect protocol-level mistakes early with runtime checks for message and tool-call invariants.
Latest version: 12.0.0

# @sisu-ai/mw-invariants

Detect protocol-level mistakes early with runtime checks for message and tool-call invariants.

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## Setup
```bash
npm i @sisu-ai/mw-invariants
```

## Exports
- `toolCallInvariant({ strict?: boolean })`
  - `strict: false` (default) logs a warning and continues.
  - `strict: true` throws an error to fail fast.


## What It Does
- Validates the tool-calling protocol in your transcript after a step completes.
- Specifically: for each assistant message that includes `tool_calls`, ensures a matching `tool` message exists later for every call.
- Reports violations via warning logs or by throwing (strict mode).

## How It Works
`toolCallInvariant({ strict })` runs after `await next()` and inspects `ctx.messages`:
- Scans assistant messages with `tool_calls`.
- For each call, looks forward for a `tool` message that matches by `tool_call_id` (preferred) or `name` (fallback for providers without IDs).
- If any are missing, either logs a warning with details or throws when `strict: true`.

This is a development-time safety net to catch mis-ordered or missing tool replies in your loop.

## Example
```ts
import 'dotenv/config';
import { Agent, createConsoleLogger, InMemoryKV, NullStream, SimpleTools, type Ctx } from '@sisu-ai/core';
import { openAIAdapter } from '@sisu-ai/adapter-openai';
import { inputToMessage } from '@sisu-ai/mw-conversation-buffer';
import { registerTools } from '@sisu-ai/mw-register-tools';
import { toolCalling } from '@sisu-ai/mw-tool-calling';
import { toolCallInvariant } from '@sisu-ai/mw-invariants';

const model = openAIAdapter({ model: 'gpt-5.4' });

// Example tool
const echo = {
  name: 'echo',
  description: 'Echo back a message',
  schema: { type: 'object', properties: { text: { type: 'string' } }, required: ['text'] },
  handler: async ({ text }: { text: string }) => ({ text })
};

const ctx: Ctx = {
  input: 'Call the echo tool with text "hello" then answer briefly.',
  messages: [{ role: 'system', content: 'Be concise.' }],
  model,
  tools: new SimpleTools(),
  memory: new InMemoryKV(),
  stream: new NullStream(),
  state: {},
  signal: new AbortController().signal,
  log: createConsoleLogger({ level: 'info' })
};

const app = new Agent()
  .use(inputToMessage)
  .use(registerTools([echo as any]))
  .use(toolCalling) // or iterativeToolCalling
  // After tool loop completes, assert that every tool_call got a tool reply
  .use(toolCallInvariant({ strict: true }));

await app.handler()(ctx);
```

## Placement & Ordering
- Place after your tool-calling middleware so it can verify the result of a turn.
- Use `strict: true` in development and CI to catch regressions early; relax to warnings in production if you prefer resilience over hard failures.

## When To Use
- During development/CI to ensure your tool loop respects the provider protocol.
- In staging/production as a warning-only monitor to surface unexpected provider behavior.

## When Not To Use
- If your app never uses tools.
- If you handle protocol validation elsewhere (e.g., custom loop with its own assertions).

## Notes & Gotchas
- Matching strategy: prefers `tool_call_id`. Falls back to `name` when the provider omits ids.
- Parallel calls: works with multiple tool calls; each must have a corresponding `tool` message.
- Cross-turn behavior: invariant checks within a single turn. If you intentionally defer tool responses to a later request, adjust placement or disable strict mode.
- Streaming: this runs post-`next()`. For streaming loops that push an `assistant_message` event, ensure that the final message is added to `ctx.messages` before this check or defer the check to the end of the run.

# Community & Support

Discover what you can do through examples or documentation. Check it out at https://github.com/finger-gun/sisu. Example projects live under [`examples/`](https://github.com/finger-gun/sisu/tree/main/examples) in the repo.

- [Code of Conduct](https://github.com/finger-gun/sisu/blob/main/CODE_OF_CONDUCT.md)
- [Contributing Guide](https://github.com/finger-gun/sisu/blob/main/CONTRIBUTING.md)
- [License](https://github.com/finger-gun/sisu/blob/main/LICENSE)
- [Report a Bug](https://github.com/finger-gun/sisu/issues/new?template=bug_report.md)
- [Request a Feature](https://github.com/finger-gun/sisu/issues/new?template=feature_request.md)

---

## Documentation

**Core** — [Package docs](packages/core/README.md) · [Error types](packages/core/ERROR_TYPES.md)

**Adapters** — [OpenAI](packages/adapters/openai/README.md) · [Anthropic](packages/adapters/anthropic/README.md) · [Ollama](packages/adapters/ollama/README.md)

<details>
<summary>All middleware packages</summary>

- [@sisu-ai/mw-agent-run-api](packages/middleware/agent-run-api/README.md)
- [@sisu-ai/mw-context-compressor](packages/middleware/context-compressor/README.md)
- [@sisu-ai/mw-control-flow](packages/middleware/control-flow/README.md)
- [@sisu-ai/mw-conversation-buffer](packages/middleware/conversation-buffer/README.md)
- [@sisu-ai/mw-cors](packages/middleware/cors/README.md)
- [@sisu-ai/mw-error-boundary](packages/middleware/error-boundary/README.md)
- [@sisu-ai/mw-guardrails](packages/middleware/guardrails/README.md)
- [@sisu-ai/mw-invariants](packages/middleware/invariants/README.md)
- [@sisu-ai/mw-orchestration](packages/middleware/orchestration/README.md)
- [@sisu-ai/mw-rag](packages/middleware/rag/README.md)
- [@sisu-ai/mw-react-parser](packages/middleware/react-parser/README.md)
- [@sisu-ai/mw-register-tools](packages/middleware/register-tools/README.md)
- [@sisu-ai/mw-tool-calling](packages/middleware/tool-calling/README.md)
- [@sisu-ai/mw-trace-viewer](packages/middleware/trace-viewer/README.md)
- [@sisu-ai/mw-usage-tracker](packages/middleware/usage-tracker/README.md)
</details>

<details>
<summary>All tool packages</summary>

- [@sisu-ai/tool-aws-s3](packages/tools/aws-s3/README.md)
- [@sisu-ai/tool-azure-blob](packages/tools/azure-blob/README.md)
- [@sisu-ai/tool-extract-urls](packages/tools/extract-urls/README.md)
- [@sisu-ai/tool-github-projects](packages/tools/github-projects/README.md)
- [@sisu-ai/tool-rag](packages/tools/rag/README.md)
- [@sisu-ai/tool-summarize-text](packages/tools/summarize-text/README.md)
- [@sisu-ai/tool-terminal](packages/tools/terminal/README.md)
- [@sisu-ai/tool-web-fetch](packages/tools/web-fetch/README.md)
- [@sisu-ai/tool-web-search-duckduckgo](packages/tools/web-search-duckduckgo/README.md)
- [@sisu-ai/tool-web-search-google](packages/tools/web-search-google/README.md)
- [@sisu-ai/tool-web-search-openai](packages/tools/web-search-openai/README.md)
- [@sisu-ai/tool-wikipedia](packages/tools/wikipedia/README.md)
</details>

<details>
<summary>All RAG packages</summary>

- [@sisu-ai/rag-core](packages/rag/core/README.md)
</details>

<details>
<summary>All vector packages</summary>

- [@sisu-ai/vector-core](packages/vector/core/README.md)
- [@sisu-ai/vector-chroma](packages/vector/chroma/README.md)
</details>

<details>
<summary>All examples</summary>

**Anthropic** — [hello](examples/anthropic-hello/README.md) · [control-flow](examples/anthropic-control-flow/README.md) · [stream](examples/anthropic-stream/README.md) · [weather](examples/anthropic-weather/README.md)

**Ollama** — [hello](examples/ollama-hello/README.md) · [stream](examples/ollama-stream/README.md) · [vision](examples/ollama-vision/README.md) · [weather](examples/ollama-weather/README.md) · [web-search](examples/ollama-web-search/README.md)

**OpenAI** — [hello](examples/openai-hello/README.md) · [weather](examples/openai-weather/README.md) · [stream](examples/openai-stream/README.md) · [vision](examples/openai-vision/README.md) · [reasoning](examples/openai-reasoning/README.md) · [react](examples/openai-react/README.md) · [control-flow](examples/openai-control-flow/README.md) · [branch](examples/openai-branch/README.md) · [parallel](examples/openai-parallel/README.md) · [graph](examples/openai-graph/README.md) · [orchestration](examples/openai-orchestration/README.md) · [orchestration-adaptive](examples/openai-orchestration-adaptive/README.md) · [guardrails](examples/openai-guardrails/README.md) · [error-handling](examples/openai-error-handling/README.md) · [rag-chroma](examples/openai-rag-chroma/README.md) · [web-search](examples/openai-web-search/README.md) · [web-fetch](examples/openai-web-fetch/README.md) · [wikipedia](examples/openai-wikipedia/README.md) · [terminal](examples/openai-terminal/README.md) · [github-projects](examples/openai-github-projects/README.md) · [server](examples/openai-server/README.md) · [aws-s3](examples/openai-aws-s3/README.md) · [azure-blob](examples/openai-azure-blob/README.md)
</details>

---

## Contributing

We build Sisu in the open. Contributions welcome.

[Contributing Guide](CONTRIBUTING.md) · [Report a Bug](https://github.com/finger-gun/sisu/issues/new?template=bug_report.md) · [Request a Feature](https://github.com/finger-gun/sisu/issues/new?template=feature_request.md) · [Code of Conduct](CODE_OF_CONDUCT.md)

---

<div align="center">

**[Star on GitHub](https://github.com/finger-gun/sisu)** if Sisu helps you build better agents.

*Quiet, determined, relentlessly useful.*

[Apache 2.0 License](LICENSE)

</div>