Add gt feed command for activity streaming (gt-3pm0f)

Wraps bd activity with Gas Town integration:
- Default follow mode for streaming
- --rig flag to target specific rig beads
- Passthrough of bd activity flags (--since, --mol, --type, --limit)

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

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

internal/cmd/feed.go

@@ -0,0 +1,141 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"syscall"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/workspace"
+)
+
+var (
+	feedFollow   bool
+	feedLimit    int
+	feedSince    string
+	feedMol      string
+	feedType     string
+	feedRig      string
+	feedNoFollow bool
+)
+
+func init() {
+	rootCmd.AddCommand(feedCmd)
+
+	feedCmd.Flags().BoolVarP(&feedFollow, "follow", "f", false, "Stream events in real-time (default when no other flags)")
+	feedCmd.Flags().BoolVar(&feedNoFollow, "no-follow", false, "Show events once and exit")
+	feedCmd.Flags().IntVarP(&feedLimit, "limit", "n", 100, "Maximum number of events to show")
+	feedCmd.Flags().StringVar(&feedSince, "since", "", "Show events since duration (e.g., 5m, 1h, 30s)")
+	feedCmd.Flags().StringVar(&feedMol, "mol", "", "Filter by molecule/issue ID prefix")
+	feedCmd.Flags().StringVar(&feedType, "type", "", "Filter by event type (create, update, delete, comment)")
+	feedCmd.Flags().StringVar(&feedRig, "rig", "", "Run from specific rig's beads directory")
+}
+
+var feedCmd = &cobra.Command{
+	Use:     "feed",
+	GroupID: GroupDiag,
+	Short:   "Show real-time activity feed from beads",
+	Long: `Display a real-time feed of issue and molecule state changes.
+
+This command wraps 'bd activity' to show mutations as they happen,
+providing visibility into workflow progress across Gas Town.
+
+By default, streams in follow mode. Use --no-follow to show events once.
+
+Event symbols:
+  +  created/bonded  - New issue or molecule created
+  →  in_progress     - Work started on an issue
+  ✓  completed       - Issue closed or step completed
+  ✗  failed          - Step or issue failed
+  ⊘  deleted         - Issue removed
+
+Examples:
+  gt feed                       # Stream all events (default: --follow)
+  gt feed --no-follow           # Show last 100 events and exit
+  gt feed --since 1h            # Events from last hour
+  gt feed --mol gt-xyz          # Filter by issue prefix
+  gt feed --rig gastown         # Use gastown rig's beads`,
+	RunE: runFeed,
+}
+
+func runFeed(cmd *cobra.Command, args []string) error {
+	// Find bd binary
+	bdPath, err := exec.LookPath("bd")
+	if err != nil {
+		return fmt.Errorf("bd not found in PATH: %w", err)
+	}
+
+	// Determine working directory
+	workDir, err := os.Getwd()
+	if err != nil {
+		return fmt.Errorf("getting current directory: %w", err)
+	}
+
+	// If --rig specified, find that rig's beads directory
+	if feedRig != "" {
+		townRoot, err := workspace.FindFromCwdOrError()
+		if err != nil {
+			return fmt.Errorf("not in a Gas Town workspace: %w", err)
+		}
+
+		// Try common beads locations for the rig
+		candidates := []string{
+			fmt.Sprintf("%s/%s/mayor/rig", townRoot, feedRig),
+			fmt.Sprintf("%s/%s", townRoot, feedRig),
+		}
+
+		found := false
+		for _, candidate := range candidates {
+			if _, err := os.Stat(candidate + "/.beads"); err == nil {
+				workDir = candidate
+				found = true
+				break
+			}
+		}
+
+		if !found {
+			return fmt.Errorf("rig '%s' not found or has no .beads directory", feedRig)
+		}
+	}
+
+	// Build bd activity command args
+	bdArgs := []string{"bd", "activity"}
+
+	// Default to follow mode unless --no-follow or other display flags set
+	shouldFollow := !feedNoFollow
+	if feedFollow {
+		shouldFollow = true
+	}
+
+	if shouldFollow {
+		bdArgs = append(bdArgs, "--follow")
+	}
+
+	if feedLimit != 100 {
+		bdArgs = append(bdArgs, "--limit", fmt.Sprintf("%d", feedLimit))
+	}
+
+	if feedSince != "" {
+		bdArgs = append(bdArgs, "--since", feedSince)
+	}
+
+	if feedMol != "" {
+		bdArgs = append(bdArgs, "--mol", feedMol)
+	}
+
+	if feedType != "" {
+		bdArgs = append(bdArgs, "--type", feedType)
+	}
+
+	// Use exec to replace the current process with bd
+	// This gives clean signal handling and terminal control
+	env := os.Environ()
+
+	// Change to the target directory before exec
+	if err := os.Chdir(workDir); err != nil {
+		return fmt.Errorf("changing to directory %s: %w", workDir, err)
+	}
+
+	return syscall.Exec(bdPath, bdArgs, env)
+}