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Description

## Problem
Several Phase 1-3 replay features were implemented in CLI but not exposed via API.

## Missing API Support

### 1. Simulate API missing --resume-from (Issue #217)
**CLI has:** hwe replay --simulate --resume-from STEP_NAME
**API needs:** POST /workflows/{id}/simulate should accept resume_from body parameter

### 2. Replay API missing --include-children (Issue #221)
**CLI has:** hwe replay --include-children
**API needs:** GET /workflows/{id}/replay?include_children=true should return workflow tree

### 3. Replay API missing --list-steps (Issue #217)
**CLI has:** hwe replay --list-steps
**API needs:** GET /workflows/{id}/replay/steps endpoint to list checkpointed steps

### 4. Variable query missing version info (Issue #222)
**Current:** GET /query/{id}/variables returns value only
**Needs:** Return {value, version} for optimistic locking support

### 5. No lock history endpoint (Issue #218)
**Needs:** GET /workflows/{id}/locks to view lock_acquired/lock_released events

### 6. No saga/compensation history endpoint (Issue #214)
**Needs:** GET /workflows/{id}/sagas to view saga_started/compensation events

## Affected Issues
#214, #217, #218, #221, #222

## Implementation Notes
- replay.py already has /replay and /simulate endpoints - extend them
- queries.py has variable query - add version field
- New endpoints needed for locks and sagas

## Effort: Medium

Due Date (YYYY-MM-DD)

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Edit Issue #223