Implement handoffs using pinned beads (gt-cu7r)

Replace mail-based handoff system with pinned beads that persist
across sessions. This fixes the issue where handoff messages get
closed before successors can read them.

Changes:
- beads: Add StatusPinned constant and handoff functions:
  - HandoffBeadTitle() for well-known naming
  - FindHandoffBead() to locate role handoff bead
  - GetOrCreateHandoffBead() to ensure bead exists
  - UpdateHandoffContent() to set handoff message
  - ClearHandoffContent() to reset after reading

- cmd/handoff: Update to use pinned beads instead of mail
  - sendHandoffMail() now updates pinned bead content

- cmd/prime: Display handoff content on startup
  - outputHandoffContent() reads and shows handoff bead

- cmd/rig: Add reset command with --handoff flag
  - gt rig reset --handoff clears handoff content

Generated with Claude Code

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

internal/cmd/prime.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/beads"
 	"github.com/steveyegge/gastown/internal/style"
 	"github.com/steveyegge/gastown/internal/templates"
 	"github.com/steveyegge/gastown/internal/workspace"
@@ -71,7 +72,14 @@ func runPrime(cmd *cobra.Command, args []string) error {
 	ctx := detectRole(cwd, townRoot)
 
 	// Output context
-	return outputPrimeContext(ctx)
+	if err := outputPrimeContext(ctx); err != nil {
+		return err
+	}
+
+	// Output handoff content if present
+	outputHandoffContent(ctx)
+
+	return nil
 }
 
 func detectRole(cwd, townRoot string) RoleContext {
@@ -307,3 +315,31 @@ func outputUnknownContext(ctx RoleContext) {
 	fmt.Println()
 	fmt.Printf("Town root: %s\n", style.Dim.Render(ctx.TownRoot))
 }
+
+// outputHandoffContent reads and displays the pinned handoff bead for the role.
+func outputHandoffContent(ctx RoleContext) {
+	if ctx.Role == RoleUnknown {
+		return
+	}
+
+	// Get role key for handoff bead lookup
+	roleKey := string(ctx.Role)
+
+	bd := beads.New(ctx.TownRoot)
+	issue, err := bd.FindHandoffBead(roleKey)
+	if err != nil {
+		// Silently skip if beads lookup fails (might not be a beads repo)
+		return
+	}
+	if issue == nil || issue.Description == "" {
+		// No handoff content
+		return
+	}
+
+	// Display handoff content
+	fmt.Println()
+	fmt.Printf("%s\n\n", style.Bold.Render("## 🤝 Handoff from Previous Session"))
+	fmt.Println(issue.Description)
+	fmt.Println()
+	fmt.Println(style.Dim.Render("(Clear with: gt rig reset --handoff)"))
+}