# redo
## Description
Restores the last undone action in a session. Only available after undo has been called. Works in conjunction with undo for full command history navigation within a session.
## Input Schema
```typescript
{
sessionId: string // Required: e.g., "session-2025-12-11-001"
}
```
**Required**: `sessionId`
**Optional**: (none)
## Output Schema
```typescript
{
content: [
{
"type": "text",
"text": JSON
}
]
}
```
**JSON structure:**
```typescript
{
success: boolean,
sessionId: string,
redoneAction: {
type: string, // e.g., "generate", "parameter_change", "rollback"
description: string,
timestamp: string // Original timestamp of the action
},
currentState: {
iterationIndex: number,
iterationCount: number,
lastPrompt?: string
},
undoStackAvailable: number, // How many undos now available again
redoStackRemaining: number // How many more redos possible
}
```
## Examples
### Example 1: Redo after single undo
**Input:**
```json
{
"sessionId": "session-2025-12-11-001"
}
```
**Output:**
```json
{
"content": [
{
"type": "text",
"text": "{\"success\":true,\"sessionId\":\"session-2025-12-11-001\",\"redoneAction\":{\"type\":\"generate\",\"description\":\"Generated image with prompt 'Cyberpunk city at night'\",\"timestamp\":\"2025-12-11T14:50:15.123Z\"},\"currentState\":{\"iterationIndex\":10,\"iterationCount\":11,\"lastPrompt\":\"Cyberpunk city at night\"},\"undoStackAvailable\":10,\"redoStackRemaining\":0}"
}
]
}
```
### Example 2: Redo after multiple undos
**Input:**
```json
{
"sessionId": "session-2025-12-11-001"
}
```
**Output:**
```json
{
"content": [
{
"type": "text",
"text": "{\"success\":true,\"sessionId\":\"session-2025-12-11-001\",\"redoneAction\":{\"type\":\"generate\",\"description\":\"Generated image with prompt 'Landscape variant 2'\",\"timestamp\":\"2025-12-11T14:45:22.789Z\"},\"currentState\":{\"iterationIndex\":9,\"iterationCount\":10,\"lastPrompt\":\"Landscape variant 2\"},\"undoStackAvailable\":9,\"redoStackRemaining\":2}"
}
]
}
```
### Example 3: Redo with no redo stack available
**Input:**
```json
{
"sessionId": "session-2025-12-11-002"
}
```
**Output:**
```json
{
"content": [
{
"type": "text",
"text": "{\"success\":false,\"error\":\"Nothing to redo\",\"sessionId\":\"session-2025-12-11-002\",\"undoStackAvailable\":5,\"redoStackRemaining\":0}"
}
]
}
```
### Example 4: Redo clears after new generation (redo stack lost)
**Input (step 1: undo):**
```json
{
"sessionId": "session-2025-12-11-001"
}
```
**Output (after undo):**
```json
{
"content": [
{
"type": "text",
"text": "{\"redoStackRemaining\":1}"
}
]
}
```
**Input (step 2: generate new image - redo stack cleared):**
```json
{
"prompt": "A new direction entirely",
"sessionId": "session-2025-12-11-001"
}
```
**Input (step 3: try to redo - fails):**
```json
{
"sessionId": "session-2025-12-11-001"
}
```
**Output (redo stack is gone):**
```json
{
"content": [
{
"type": "text",
"text": "{\"success\":false,\"error\":\"Nothing to redo\",\"sessionId\":\"session-2025-12-11-001\",\"redoStackRemaining\":0}"
}
]
}
```
## Error Cases
- **Session not found**: Invalid sessionId
- **Nothing to redo**: Redo stack is empty (no prior undo, or new action performed after undo)
- **Redo stack cleared**: New action performed after undo clears the redo buffer
## Notes
- Redo stack is **cleared immediately** when any new operation occurs
- This follows standard editor behavior (VS Code, Figma, etc.)
- Maximum redo depth matches undo depth (50 operations)
- Very fast operation, typically <10ms
- Redo stack is session-specific and ephemeral (not persisted)
- Useful for quick A/B testing: Undo variant A, Redo variant A, then try variant B
- Pair with undo for full workflow control in iterative image generation
