stacklok / toolhive
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web-flow 
Advanced Workflow Features for vMCP Composition (#2592)

## Overview

Implements advanced workflow features for Virtual MCP Composite Tools, including DAG-based parallel execution, step dependencies, sophisticated error handling, and workflow state management. This completes Phase 2 of the composition work.

**Issue**: Closes #156 (stacklok/stacklok-epics)

## What Changed

### Core Features

#### 1. DAG-Based Parallel Execution
- **New file**: [pkg/vmcp/composer/dag_executor.go](pkg/vmcp/composer/dag_executor.go)
  - Implements topological sort using Kahn's algorithm to build execution levels
  - Executes independent steps in parallel using `errgroup` for coordination
  - Semaphore-based concurrency limiting (default: 10 parallel steps)
  - Automatic optimization: steps with no dependencies run concurrently
  - Performance improvement: parallel execution reduces workflow time by ~60-70% for independent steps

#### 2. Step Dependencies
- `depends_on` field support in [pkg/vmcp/composer/composer.go:67](pkg/vmcp/composer/composer.go#L67)
- Dependency graph validation with cycle detection using DFS
- Transitive dependencies automatically handled
- Missing dependency validation at workflow definition time

#### 3. Advanced Error Handling
- **Three-level error handling**:
  - Step-level: `on_error.continue_on_error` overrides workflow-level settings
  - Workflow-level: `failure_mode` (abort/continue/best_effort)
  - Automatic: retry with exponential backoff
- **Retry logic** in [pkg/vmcp/composer/workflow_engine.go:311-350](pkg/vmcp/composer/workflow_engine.go#L311-L350):
  - Configurable retry count and initial delay
  - Exponential backoff (2^attempt * initial_delay, max 60x)
  - Safety cap: maximum 10 retries to prevent infinite loops

#### 4. Workflow State Management
- **Pluggable state store interface**: [pkg/vmcp/composer/composer.go:191-217](pkg/vmcp/composer/composer.go#L191-L217)
- **In-memory implementation**: [pkg/vmcp/composer/state_store.go](... (continued)

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19379293047 main Advanced Workflow Features for vMCP Composition (#2592) ## Overview Implements advanced workflow features for Virtual MCP Composite Tools, including DAG-based parallel execution, step dependencies, sophisticated error handling, and workflow stat... push web-flow github
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19378966908 converts-mcpgroup-e2e-tests-to-int Merge f66c2f011 into acf850270 Pull #2594 web-flow github
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19378708933 converts-mcpgroup-e2e-tests-to-int Merge 39b24ba40 into acf850270 Pull #2594 web-flow github
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19377968580 converts-mcpgroup-e2e-tests-to-int Merge 75119b385 into acf850270 Pull #2594 web-flow github
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19377963163 converts-mcpgroup-e2e-tests-to-int Merge 8709db2c3 into acf850270 Pull #2594 web-flow github
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19376910474 main Adds caching to make CI actions faster when downloading dependencies (#2583) implements caching for go dependencies Signed-off-by: ChrisJBurns <29541485+ChrisJBurns@users.noreply.github.com> push web-flow github
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19376368395 issue_156_docs_2025-11-14 Merge a03b1cdbf into 82c6f846d Pull #2593 web-flow github
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19376280296 issue_156_2025-11-13 Merge 3416f804f into 82c6f846d Pull #2592 web-flow github
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19376233201 issue_156_2025-11-13 Merge f8f3f53a3 into 82c6f846d Pull #2592 web-flow github
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19375884851 poc-faster-build Merge 602089a3d into 82c6f846d Pull #2583 web-flow github
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