stacklok / toolhive / 19656702397

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Fix YAML parsing and workflow conversion for composite tool output configuration (#2715)

Fixes two missing pieces that prevented structured output schemas from working:

1. YAML Parsing (pkg/vmcp/config/yaml_loader.go):
   - Added Output field to rawCompositeTool struct
   - Added rawOutputConfig and rawOutputProperty structs
   - Implemented transformOutputConfig() and transformOutputProperty()
   - Updated transformCompositeTools() to parse output config

2. Workflow Conversion (pkg/vmcp/server/workflow_converter.go):
   - Added Output field assignment when converting CompositeToolConfig
     to WorkflowDefinition (this was missing from PR #2677)

Without these changes, the output config was:
- Parsed from YAML but never transformed (yaml_loader.go)
- Transformed but never copied to WorkflowDefinition (workflow_converter.go)

This caused def.Output to always be nil in the workflow engine, triggering
backward compatibility mode which returns the last step's raw output.

Testing:
- Added comprehensive unit tests for YAML output config transformation
- Added tests for workflow converter output field copying
- All existing tests pass
- Verified backward compatibility (nil output still works)

Limitations (separate issue needed):
- Workflow metadata ({{.workflow.duration_ms}}, {{.workflow.step_count}})
  is not yet available in template context during output construction
- These fields are calculated AFTER output construction completes
- Requires refactoring workflow_engine.go to populate workflow metadata
  before calling constructOutputFromConfig()

Fixes: #2713

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

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