fix(beads): add CreateOrReopenAgentBead for polecat re-spawn (#333)

When a polecat is nuked and re-spawned with the same name, CreateAgentBead
fails with a UNIQUE constraint error because the old agent bead exists as
a tombstone.

This adds CreateOrReopenAgentBead that:
1. First tries to create the agent bead normally
2. If UNIQUE constraint fails, reopens the existing bead and updates fields

Updated both spawn paths in polecat manager to use the new function.

Fixes #332

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

internal/beads/beads_agent.go

@@ -176,6 +176,67 @@ func (b *Beads) CreateAgentBead(id, title string, fields *AgentFields) (*Issue,
 	return &issue, nil
 }
 
+// CreateOrReopenAgentBead creates an agent bead or reopens an existing one.
+// This handles the case where a polecat is nuked and re-spawned with the same name:
+// the old agent bead exists as a tombstone, so we reopen and update it instead of
+// failing with a UNIQUE constraint error.
+//
+// The function:
+// 1. Tries to create the agent bead
+// 2. If UNIQUE constraint fails, reopens the existing bead and updates its fields
+func (b *Beads) CreateOrReopenAgentBead(id, title string, fields *AgentFields) (*Issue, error) {
+	// First try to create the bead
+	issue, err := b.CreateAgentBead(id, title, fields)
+	if err == nil {
+		return issue, nil
+	}
+
+	// Check if it's a UNIQUE constraint error
+	if !strings.Contains(err.Error(), "UNIQUE constraint failed") {
+		return nil, err
+	}
+
+	// The bead already exists (likely a tombstone from a previous nuked polecat)
+	// Reopen it and update its fields
+	if _, reopenErr := b.run("reopen", id, "--reason=re-spawning agent"); reopenErr != nil {
+		// If reopen fails, the bead might already be open - continue with update
+		if !strings.Contains(reopenErr.Error(), "already open") {
+			return nil, fmt.Errorf("reopening existing agent bead: %w (original error: %v)", reopenErr, err)
+		}
+	}
+
+	// Update the bead with new fields
+	description := FormatAgentDescription(title, fields)
+	updateOpts := UpdateOptions{
+		Title:       &title,
+		Description: &description,
+	}
+	if err := b.Update(id, updateOpts); err != nil {
+		return nil, fmt.Errorf("updating reopened agent bead: %w", err)
+	}
+
+	// Set the role slot if specified
+	if fields != nil && fields.RoleBead != "" {
+		if _, err := b.run("slot", "set", id, "role", fields.RoleBead); err != nil {
+			// Non-fatal: warn but continue
+			fmt.Printf("Warning: could not set role slot: %v\n", err)
+		}
+	}
+
+	// Set the hook slot if specified
+	if fields != nil && fields.HookBead != "" {
+		// Clear any existing hook first, then set new one
+		_, _ = b.run("slot", "clear", id, "hook")
+		if _, err := b.run("slot", "set", id, "hook", fields.HookBead); err != nil {
+			// Non-fatal: warn but continue
+			fmt.Printf("Warning: could not set hook slot: %v\n", err)
+		}
+	}
+
+	// Return the updated bead
+	return b.Show(id)
+}
+
 // UpdateAgentState updates the agent_state field in an agent bead.
 // Optionally updates hook_bead if provided.
 //