Add BD_ACTOR env var default for created_by field enforcement (gt-6r18e.6)

- Create() function now defaults Actor from BD_ACTOR env var when not provided
- CreateAgentBead() now passes --actor flag from BD_ACTOR for provenance tracking
- This ensures created_by is populated on all issue creation paths

Affects: merge requests, escalations, digests, agent beads, molecule steps

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

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

internal/beads/beads.go

@@ -404,6 +404,8 @@ func (b *Beads) Blocked() ([]*Issue, error) {
 }
 
 // Create creates a new issue and returns it.
+// If opts.Actor is empty, it defaults to the BD_ACTOR environment variable.
+// This ensures created_by is populated for issue provenance tracking.
 func (b *Beads) Create(opts CreateOptions) (*Issue, error) {
 	args := []string{"create", "--json"}
 
@@ -422,8 +424,13 @@ func (b *Beads) Create(opts CreateOptions) (*Issue, error) {
 	if opts.Parent != "" {
 		args = append(args, "--parent="+opts.Parent)
 	}
-	if opts.Actor != "" {
-		args = append(args, "--actor="+opts.Actor)
+	// Default Actor from BD_ACTOR env var if not specified
+	actor := opts.Actor
+	if actor == "" {
+		actor = os.Getenv("BD_ACTOR")
+	}
+	if actor != "" {
+		args = append(args, "--actor="+actor)
 	}
 
 	out, err := b.run(args...)
@@ -784,6 +791,7 @@ func ParseAgentFields(description string) *AgentFields {
 // CreateAgentBead creates an agent bead for tracking agent lifecycle.
 // The ID format is: <prefix>-<rig>-<role>-<name> (e.g., gt-gastown-polecat-Toast)
 // Use AgentBeadID() helper to generate correct IDs.
+// The created_by field is populated from BD_ACTOR env var for provenance tracking.
 func (b *Beads) CreateAgentBead(id, title string, fields *AgentFields) (*Issue, error) {
 	description := FormatAgentDescription(title, fields)
 
@@ -794,6 +802,11 @@ func (b *Beads) CreateAgentBead(id, title string, fields *AgentFields) (*Issue,
 		"--description=" + description,
 	}
 
+	// Default actor from BD_ACTOR env var for provenance tracking
+	if actor := os.Getenv("BD_ACTOR"); actor != "" {
+		args = append(args, "--actor="+actor)
+	}
+
 	out, err := b.run(args...)
 	if err != nil {
 		return nil, err