fix: auto-create agent bead when bd agent state called on non-existent agent

Previously, `bd agent state <agent> <state>` would fail if the agent bead
didn't exist in the database. This caused issues when `gt sling` tried to
update agent state for newly spawned polecats.

Now when the agent doesn't exist:
1. Parse role_type and rig from the agent ID (e.g., gt-gastown-polecat-nux)
2. Auto-create the agent bead with type=agent
3. Add role_type and rig labels for filtering (bd list --label=role_type:polecat)
4. Continue with the state update

This enables:
- Work history accumulation per polecat name
- Skill/success tracking over time
- `bd list --type=agent` to see all agents

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

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

cmd/bd/agent_test.go

@@ -48,3 +48,95 @@ func TestFormatTimeOrNil(t *testing.T) {
 		t.Errorf("expected nil for nil time, got %v", result)
 	}
 }
+
+func TestParseAgentIDFields(t *testing.T) {
+	tests := []struct {
+		name         string
+		agentID      string
+		wantRoleType string
+		wantRig      string
+	}{
+		// Town-level roles
+		{
+			name:         "town-level mayor",
+			agentID:      "gt-mayor",
+			wantRoleType: "mayor",
+			wantRig:      "",
+		},
+		{
+			name:         "town-level deacon",
+			agentID:      "bd-deacon",
+			wantRoleType: "deacon",
+			wantRig:      "",
+		},
+		// Per-rig singleton roles
+		{
+			name:         "rig-level witness",
+			agentID:      "gt-gastown-witness",
+			wantRoleType: "witness",
+			wantRig:      "gastown",
+		},
+		{
+			name:         "rig-level refinery",
+			agentID:      "bd-beads-refinery",
+			wantRoleType: "refinery",
+			wantRig:      "beads",
+		},
+		// Per-rig named roles
+		{
+			name:         "named polecat",
+			agentID:      "gt-gastown-polecat-nux",
+			wantRoleType: "polecat",
+			wantRig:      "gastown",
+		},
+		{
+			name:         "named crew",
+			agentID:      "bd-beads-crew-dave",
+			wantRoleType: "crew",
+			wantRig:      "beads",
+		},
+		{
+			name:         "polecat with hyphenated name",
+			agentID:      "gt-gastown-polecat-nux-123",
+			wantRoleType: "polecat",
+			wantRig:      "gastown",
+		},
+		// Edge cases
+		{
+			name:         "no hyphen",
+			agentID:      "invalid",
+			wantRoleType: "",
+			wantRig:      "",
+		},
+		{
+			name:         "empty string",
+			agentID:      "",
+			wantRoleType: "",
+			wantRig:      "",
+		},
+		{
+			name:         "unknown role",
+			agentID:      "gt-gastown-unknown",
+			wantRoleType: "",
+			wantRig:      "",
+		},
+		{
+			name:         "prefix only",
+			agentID:      "gt-",
+			wantRoleType: "",
+			wantRig:      "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotRoleType, gotRig := parseAgentIDFields(tt.agentID)
+			if gotRoleType != tt.wantRoleType {
+				t.Errorf("parseAgentIDFields(%q) roleType = %q, want %q", tt.agentID, gotRoleType, tt.wantRoleType)
+			}
+			if gotRig != tt.wantRig {
+				t.Errorf("parseAgentIDFields(%q) rig = %q, want %q", tt.agentID, gotRig, tt.wantRig)
+			}
+		})
+	}
+}