Add gt seance command for predecessor session discovery (gt-7qvd7)

Parses Claude Code ~/.claude/projects/ to find Gas Town sessions.
Sessions are identified by the [GAS TOWN] beacon in startup messages.

Features:
- Filter by role (crew, polecat, witness, etc.)
- Filter by rig name
- Show recent N sessions
- JSON output for scripting
- Sorts by most recent first

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

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

internal/cmd/seance.go

@@ -0,0 +1,170 @@
+package cmd
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/claude"
+	"github.com/steveyegge/gastown/internal/style"
+)
+
+var (
+	seanceAll    bool
+	seanceRole   string
+	seanceRig    string
+	seanceRecent int
+	seanceJSON   bool
+)
+
+var seanceCmd = &cobra.Command{
+	Use:     "seance",
+	GroupID: GroupDiag,
+	Short:   "Discover and browse predecessor sessions",
+	Long: `Find and resume predecessor Claude Code sessions.
+
+Seance scans Claude Code's session history to find Gas Town sessions.
+Sessions are identified by the [GAS TOWN] beacon sent during startup.
+
+Examples:
+  gt seance                     # List recent Gas Town sessions
+  gt seance --all               # Include non-Gas Town sessions
+  gt seance --role crew         # Filter by role type
+  gt seance --rig gastown       # Filter by rig
+  gt seance --recent 10         # Last 10 sessions
+  gt seance --json              # JSON output
+
+Resume a session in Claude Code:
+  claude --resume <session-id>
+
+The beacon format parsed:
+  [GAS TOWN] gastown/crew/joe • assigned:gt-xyz • 2025-12-30T15:42`,
+	RunE: runSeance,
+}
+
+func init() {
+	seanceCmd.Flags().BoolVarP(&seanceAll, "all", "a", false, "Include non-Gas Town sessions")
+	seanceCmd.Flags().StringVar(&seanceRole, "role", "", "Filter by role (crew, polecat, witness, etc.)")
+	seanceCmd.Flags().StringVar(&seanceRig, "rig", "", "Filter by rig name")
+	seanceCmd.Flags().IntVarP(&seanceRecent, "recent", "n", 20, "Number of recent sessions to show")
+	seanceCmd.Flags().BoolVar(&seanceJSON, "json", false, "Output as JSON")
+
+	rootCmd.AddCommand(seanceCmd)
+}
+
+func runSeance(cmd *cobra.Command, args []string) error {
+	filter := claude.SessionFilter{
+		GasTownOnly: !seanceAll,
+		Role:        seanceRole,
+		Rig:         seanceRig,
+		Limit:       seanceRecent,
+	}
+
+	sessions, err := claude.DiscoverSessions(filter)
+	if err != nil {
+		return fmt.Errorf("discovering sessions: %w", err)
+	}
+
+	if seanceJSON {
+		enc := json.NewEncoder(os.Stdout)
+		enc.SetIndent("", "  ")
+		return enc.Encode(sessions)
+	}
+
+	if len(sessions) == 0 {
+		if seanceAll {
+			fmt.Println("No sessions found.")
+		} else {
+			fmt.Println("No Gas Town sessions found.")
+			fmt.Println(style.Dim.Render("Use --all to include non-Gas Town sessions"))
+		}
+		return nil
+	}
+
+	// Print header
+	fmt.Printf("%s\n\n", style.Bold.Render("Claude Code Sessions"))
+
+	// Calculate column widths
+	idWidth := 10
+	roleWidth := 24
+	timeWidth := 16
+	topicWidth := 30
+
+	// Header row
+	fmt.Printf("%-*s  %-*s  %-*s  %-*s\n",
+		idWidth, "ID",
+		roleWidth, "ROLE",
+		timeWidth, "STARTED",
+		topicWidth, "TOPIC")
+	fmt.Printf("%s\n", strings.Repeat("─", idWidth+roleWidth+timeWidth+topicWidth+6))
+
+	for _, s := range sessions {
+		id := s.ShortID()
+
+		role := s.Role
+		if role == "" {
+			// Try to infer from path
+			role = inferRoleFromPath(s.Path)
+		}
+		if len(role) > roleWidth {
+			role = role[:roleWidth-1] + "…"
+		}
+
+		timeStr := s.FormatTime()
+
+		topic := s.Topic
+		if topic == "" && s.Summary != "" {
+			// Use summary as fallback
+			topic = s.Summary
+		}
+		if len(topic) > topicWidth {
+			topic = topic[:topicWidth-1] + "…"
+		}
+
+		// Color based on Gas Town status
+		if s.IsGasTown {
+			fmt.Printf("%-*s  %-*s  %-*s  %-*s\n",
+				idWidth, id,
+				roleWidth, role,
+				timeWidth, timeStr,
+				topicWidth, topic)
+		} else {
+			fmt.Printf("%s  %s  %s  %s\n",
+				style.Dim.Render(fmt.Sprintf("%-*s", idWidth, id)),
+				style.Dim.Render(fmt.Sprintf("%-*s", roleWidth, role)),
+				style.Dim.Render(fmt.Sprintf("%-*s", timeWidth, timeStr)),
+				style.Dim.Render(fmt.Sprintf("%-*s", topicWidth, topic)))
+		}
+	}
+
+	fmt.Printf("\n%s\n", style.Dim.Render("Resume a session: claude --resume <full-session-id>"))
+
+	return nil
+}
+
+// inferRoleFromPath attempts to extract a role from the project path.
+func inferRoleFromPath(path string) string {
+	// Look for patterns like /crew/joe, /polecats/furiosa, /witness, etc.
+	parts := strings.Split(path, "/")
+	for i := len(parts) - 1; i >= 0; i-- {
+		part := parts[i]
+		switch part {
+		case "witness", "refinery", "deacon", "mayor":
+			return part
+		case "crew", "polecats":
+			if i+1 < len(parts) {
+				// Include the agent name
+				return fmt.Sprintf("%s/%s", part, parts[i+1])
+			}
+			return part
+		}
+	}
+
+	// Fall back to last path component
+	if len(parts) > 0 {
+		return parts[len(parts)-1]
+	}
+	return "unknown"
+}