feat: Add source tracing metadata to cooked steps (gt-8tmz.18)

Add SourceFormula and SourceLocation fields to track where each step
came from during the cooking process. This enables debugging of complex
compositions with inheritance, expansion, and advice.

Changes:
- Added SourceFormula and SourceLocation fields to Step struct (formula/types.go)
- Added same fields to Issue struct (types/types.go)
- Added SetSourceInfo() to parser.go - sets source on all steps after parsing
- Updated cook.go to copy source fields from Step to Issue
- Updated dry-run output to display source info: [from: formula@location]
- Updated advice.go to set source on advice-generated steps
- Updated controlflow.go to preserve source on loop-expanded steps
- Updated expand.go to preserve source on template-expanded steps

The source location format is:
- steps[N] - regular step at index N
- steps[N].children[M] - child step
- steps[N].loop.body[M] - loop body step
- template[N] - expansion template step
- advice - step inserted by advice transformation

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/formula/advice.go

@@ -166,10 +166,13 @@ func adviceStepToStep(as *AdviceStep, target *Step) *Step {
 	desc := substituteStepRef(as.Description, target)
 
 	return &Step{
-		ID:          id,
-		Title:       title,
-		Description: desc,
-		Type:        as.Type,
+		ID:            id,
+		Title:         title,
+		Description:   desc,
+		Type:          as.Type,
+		SourceFormula: target.SourceFormula, // Inherit source formula from target (gt-8tmz.18)
+		// SourceLocation will be "advice" to indicate this came from advice transformation
+		SourceLocation: "advice",
 	}
 }
 

internal/formula/controlflow.go

@@ -146,18 +146,20 @@ func expandLoopIteration(step *Step, iteration int) ([]*Step, error) {
 		iterID := fmt.Sprintf("%s.iter%d.%s", step.ID, iteration, bodyStep.ID)
 
 		clone := &Step{
-			ID:          iterID,
-			Title:       bodyStep.Title,
-			Description: bodyStep.Description,
-			Type:        bodyStep.Type,
-			Priority:    bodyStep.Priority,
-			Assignee:    bodyStep.Assignee,
-			Condition:   bodyStep.Condition,
-			WaitsFor:    bodyStep.WaitsFor,
-			Expand:      bodyStep.Expand,
-			Gate:        bodyStep.Gate,
-			Loop:        cloneLoopSpec(bodyStep.Loop), // Support nested loops (gt-zn35j)
-			OnComplete:  cloneOnComplete(bodyStep.OnComplete),
+			ID:             iterID,
+			Title:          bodyStep.Title,
+			Description:    bodyStep.Description,
+			Type:           bodyStep.Type,
+			Priority:       bodyStep.Priority,
+			Assignee:       bodyStep.Assignee,
+			Condition:      bodyStep.Condition,
+			WaitsFor:       bodyStep.WaitsFor,
+			Expand:         bodyStep.Expand,
+			Gate:           bodyStep.Gate,
+			Loop:           cloneLoopSpec(bodyStep.Loop), // Support nested loops (gt-zn35j)
+			OnComplete:     cloneOnComplete(bodyStep.OnComplete),
+			SourceFormula:  bodyStep.SourceFormula,                                                     // Preserve source (gt-8tmz.18)
+			SourceLocation: fmt.Sprintf("%s.iter%d", bodyStep.SourceLocation, iteration), // Track iteration
 		}
 
 		// Clone ExpandVars if present

internal/formula/expand.go

@@ -163,12 +163,14 @@ func expandStep(target *Step, template []*Step, depth int) ([]*Step, error) {
 
 	for _, tmpl := range template {
 		expanded := &Step{
-			ID:          substituteTargetPlaceholders(tmpl.ID, target),
-			Title:       substituteTargetPlaceholders(tmpl.Title, target),
-			Description: substituteTargetPlaceholders(tmpl.Description, target),
-			Type:        tmpl.Type,
-			Priority:    tmpl.Priority,
-			Assignee:    tmpl.Assignee,
+			ID:             substituteTargetPlaceholders(tmpl.ID, target),
+			Title:          substituteTargetPlaceholders(tmpl.Title, target),
+			Description:    substituteTargetPlaceholders(tmpl.Description, target),
+			Type:           tmpl.Type,
+			Priority:       tmpl.Priority,
+			Assignee:       tmpl.Assignee,
+			SourceFormula:  tmpl.SourceFormula,  // Preserve source from template (gt-8tmz.18)
+			SourceLocation: tmpl.SourceLocation, // Preserve source location (gt-8tmz.18)
 		}
 
 		// Substitute placeholders in labels

internal/formula/parser.go

@@ -92,6 +92,10 @@ func (p *Parser) ParseFile(path string) (*Formula, error) {
 	}
 
 	formula.Source = absPath
+
+	// Set source tracing info on all steps (gt-8tmz.18)
+	SetSourceInfo(formula)
+
 	p.cache[absPath] = formula
 
 	// Also cache by name for extends resolution
@@ -393,3 +397,30 @@ func ApplyDefaults(formula *Formula, values map[string]string) map[string]string
 
 	return result
 }
+
+// SetSourceInfo sets SourceFormula and SourceLocation on all steps in a formula.
+// Called after parsing to enable source tracing during cooking (gt-8tmz.18).
+func SetSourceInfo(formula *Formula) {
+	setSourceInfoRecursive(formula.Steps, formula.Formula, "steps")
+	// Also set source info on template steps for expansion formulas
+	setSourceInfoRecursive(formula.Template, formula.Formula, "template")
+}
+
+// setSourceInfoRecursive recursively sets source info on steps.
+func setSourceInfoRecursive(steps []*Step, formulaName, pathPrefix string) {
+	for i, step := range steps {
+		step.SourceFormula = formulaName
+		step.SourceLocation = fmt.Sprintf("%s[%d]", pathPrefix, i)
+
+		if len(step.Children) > 0 {
+			childPath := fmt.Sprintf("%s[%d].children", pathPrefix, i)
+			setSourceInfoRecursive(step.Children, formulaName, childPath)
+		}
+
+		// Handle loop body steps
+		if step.Loop != nil && len(step.Loop.Body) > 0 {
+			bodyPath := fmt.Sprintf("%s[%d].loop.body", pathPrefix, i)
+			setSourceInfoRecursive(step.Loop.Body, formulaName, bodyPath)
+		}
+	}
+}

internal/formula/types.go

@@ -188,6 +188,17 @@ type Step struct {
 	// OnComplete defines actions triggered when this step completes (gt-8tmz.8).
 	// Used for runtime expansion over step output (the for-each construct).
 	OnComplete *OnCompleteSpec `json:"on_complete,omitempty"`
+
+	// Source tracing fields (gt-8tmz.18): track where this step came from.
+	// These are set during parsing/transformation and copied to Issues during cooking.
+
+	// SourceFormula is the formula name where this step was defined.
+	// For inherited steps, this is the parent formula, not the final composed formula.
+	SourceFormula string `json:"-"` // Internal only, not serialized to JSON
+
+	// SourceLocation is the path within the source formula.
+	// Format: "steps[0]", "steps[2].children[1]", "advice[0].after", "loop.body[0]"
+	SourceLocation string `json:"-"` // Internal only, not serialized to JSON
 }
 
 // Gate defines an async wait condition (integrates with bd-udsi).

internal/types/types.go

@@ -66,6 +66,10 @@ type Issue struct {
 	AwaitID   string        `json:"await_id,omitempty"`   // Condition identifier (e.g., run ID, PR number)
 	Timeout   time.Duration `json:"timeout,omitempty"`    // Max wait time before escalation
 	Waiters   []string      `json:"waiters,omitempty"`    // Mail addresses to notify when gate clears
+
+	// Source tracing fields (gt-8tmz.18): track where this issue came from during cooking
+	SourceFormula   string `json:"source_formula,omitempty"`   // Formula name where this step was defined
+	SourceLocation  string `json:"source_location,omitempty"`  // Path within source: "steps[0]", "advice[0].after"
 }
 
 // ComputeContentHash creates a deterministic hash of the issue's content.