output-dev-step-function

What this skill does

# Creating Step Functions

## Overview

This skill documents how to create step functions in `steps.ts` for Output SDK workflows. Steps are where all I/O operations happen - HTTP requests, LLM calls, database operations, file system access, etc.

## When to Use This Skill

- Implementing I/O operations for a workflow
- Adding HTTP client integrations
- Implementing LLM-powered steps
- Handling errors with FatalError and ValidationError
- Creating reusable step components

## File Organization

### Option 1: Flat File (Default)

For smaller workflows, use a single `steps.ts` file:

```
src/workflows/{workflow-name}/
├── workflow.ts
├── steps.ts         # All steps in one file
├── types.ts
└── ...
```

### Option 2: Folder-Based (Large workflows)

For larger workflows with many steps, use a `steps/` folder:

```
src/workflows/{workflow-name}/
├── workflow.ts
├── steps/           # Steps split into individual files
│   ├── fetch_data.ts
│   ├── process.ts
│   └── validate.ts
├── types.ts
└── ...
```

## Component Location Rules

**Important**: `step()` calls MUST be in files containing 'steps' in the path:
- `src/workflows/my_workflow/steps.ts` ✓
- `src/workflows/my_workflow/steps/fetch_data.ts` ✓
- `src/shared/steps/common_steps.ts` ✓
- `src/workflows/my_workflow/helpers.ts` ✗ (cannot contain step() calls)

## Activity Isolation Constraints

Steps are Temporal activities with strict import rules to ensure deterministic replay.

### Steps CAN import from:
- Local workflow files: `./utils.js`, `./types.js`, `./helpers.js`
- Local subdirectories: `./clients/pokeapi.js`, `./lib/helpers.js`
- Shared utilities: `../../shared/utils/*.js`
- Shared clients: `../../shared/clients/*.js`
- Shared services: `../../shared/services/*.js`

### Steps CANNOT import:
- Other step files (even shared steps - workflows import those)
- Evaluator files
- Workflow files

**Example of WRONG imports:**
```typescript
// WRONG - steps cannot import other steps
import { otherStep } from '../../shared/steps/other.js'; // ✗
import { anotherStep } from './other_steps.js'; // ✗
```

## Critical Import Patterns

### Core Imports

```typescript
// CORRECT - Import from @outputai/core
import { step, z, FatalError, ValidationError } from '@outputai/core';

// WRONG - Never import z from zod
import { z } from 'zod';
```

### HTTP Client Import

```typescript
// CORRECT - Use @outputai/http wrapper
import { httpClient } from '@outputai/http';

// WRONG - Never use axios directly
import axios from 'axios';
```

**Related Skill**: `output-error-http-client`

### LLM Client Import

```typescript
// CORRECT - Use @outputai/llm wrapper
import { generateText, Output } from '@outputai/llm';

// WRONG - Never call LLM providers directly
import OpenAI from 'openai';
```

### ES Module Imports

All imports MUST use `.js` extension:

```typescript
// CORRECT
import { InputSchema, OutputSchema } from './types.js';
import { GeminiService } from '../../shared/clients/gemini_client.js';

// WRONG - Missing .js extension
import { InputSchema, OutputSchema } from './types';
```

## Basic Structure

```typescript
import { step, z, FatalError, ValidationError } from '@outputai/core';
import { httpClient } from '@outputai/http';
import { generateText, Output } from '@outputai/llm';

import { StepInputSchema, StepOutputSchema } from './types.js';

export const myStep = step( {
  name: 'myStep',
  description: 'Description of what this step does',
  inputSchema: StepInputSchema,
  outputSchema: StepOutputSchema,
  fn: async input => {
    // Implementation with I/O operations
    return { /* output matching outputSchema */ };
  }
} );
```

## Required Properties

### name (string)
Unique identifier for the step. Use camelCase.

```typescript
name: 'generateImageIdeas'
```

### description (string)
Human-readable description of the step's purpose.

```typescript
description: 'Generate creative infographic prompt ideas using Claude'
```

### inputSchema (Zod schema)
Schema for validating step input. Define in `types.ts` and import.

```typescript
inputSchema: z.object( {
  content: z.string(),
  numberOfIdeas: z.number()
} )
```

### outputSchema (Zod schema)
Schema for validating step output. Define in `types.ts` and import.

```typescript
outputSchema: z.array( z.string() )
```

### fn (async function)
The step execution function. This is where I/O operations happen.

```typescript
fn: async input => {
  const result = await someExternalService( input );
  return result;
}
```

## HTTP Client Usage

### Creating an HTTP Client

```typescript
import { httpClient } from '@outputai/http';
import { FatalError, ValidationError } from '@outputai/core';

const RETRY_STATUS_CODES = [ 408, 429, 500, 502, 503, 504 ];
const FATAL_STATUS_CODES = [ 401, 403, 404 ];

const httpClientInstance = httpClient( {
  timeout: 30000,
  retry: {
    limit: 3,
    statusCodes: RETRY_STATUS_CODES
  },
  hooks: {
    beforeError: [
      error => {
        const status = error.response?.status;
        const message = error.message;

        if ( status && FATAL_STATUS_CODES.includes( status ) ) {
          throw new FatalError(
            `HTTP ${status} error: ${message}. This is a permanent error.`
          );
        }

        throw new ValidationError(
          `HTTP request failed: ${message}`
        );
      }
    ]
  }
} );
```

### Making HTTP Requests

```typescript
// GET request
const response = await httpClientInstance.get( 'https://api.example.com/data' );
const data = await response.json();

// POST request with JSON body
const response = await httpClientInstance.post( 'https://api.example.com/submit', {
  json: { field: 'value' }
} );

// HEAD request (check URL accessibility)
const response = await httpClientInstance.head( url );
const contentType = response.headers.get( 'content-type' );
```

**Related Skill**: `output-dev-http-client-create` for creating shared clients

## LLM Operations

### Important: Define LLM Schemas in types.ts

Schemas used in `Output.object()` **must** be defined in `types.ts` and imported -- never defined inline in step functions. Inline schemas lead to duplication, drift between the step's `outputSchema` and the LLM schema, and make it harder to maintain types.

```typescript
// WRONG - inline schema in Output.object()
output: Output.object( {
  schema: z.object( {
    analysis: z.string()
  } )
} )

// CORRECT - import from types.ts
import { AnalysisLlmSchema } from './types.js';
// ...
output: Output.object( {
  schema: AnalysisLlmSchema
} )
```

### Using generateText with Output.object()

**Important**: The `variables` field only accepts `string | number | boolean` values. Arrays and objects must be pre-formatted into strings in the step before passing. See `output-dev-prompt-file` for the full constraint and examples.

```typescript
import { generateText, Output } from '@outputai/llm';
import {
  AnalyzeContentInputSchema,
  AnalyzeContentOutputSchema,
  AnalysisLlmSchema
} from './types.js';

export const analyzeContent = step( {
  name: 'analyzeContent',
  description: 'Analyze content using Claude',
  inputSchema: AnalyzeContentInputSchema,
  outputSchema: AnalyzeContentOutputSchema,
  fn: async ( { content } ) => {
    const { output } = await generateText( {
      prompt: 'analyzeContent@v1',
      variables: {
        content
      },
      output: Output.object( {
        schema: AnalysisLlmSchema
      } )
    } );

    return { analysis: output.analysis };
  }
} );
```

### Using generateText

```typescript
import { generateText } from '@outputai/llm';
import { SummarizeInputSchema, SummarizeOutputSchema } from './types.js';

export const generateSummary = step( {
  name: 'generateSummary',
  description: 'Generate a text summary',
  inputSchema: SummarizeInputSchema,
  outputSchema: SummarizeOutputSchema,
  fn: async ( { content } ) => {
    const { result } = await generateText( {
      prompt: 'summarize@v1',
      variables: { content }
    } );

    return { summary: