feat(session): Include session ID in PropulsionNudge for /resume picker

PropulsionNudgeForRole now accepts a workDir parameter and reads
session ID from .runtime/session_id to append [session:xxx] to the
nudge message. This enables Claude Code's /resume picker to discover
Gas Town sessions.

(gt-u49zh)

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

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

internal/session/names.go

@@ -1,7 +1,12 @@
 // Package session provides polecat session lifecycle management.
 package session
 
-import "fmt"
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
 
 // Prefix is the common prefix for all Gas Town tmux session names.
 const Prefix = "gt-"
@@ -50,19 +55,43 @@ func PropulsionNudge() string {
 // - witness/refinery: Start patrol cycle
 // - deacon: Start heartbeat patrol
 // - mayor: Check mail for coordination work
-func PropulsionNudgeForRole(role string) string {
+//
+// The workDir parameter is used to locate .runtime/session_id for including
+// session ID in the message (for Claude Code /resume picker discovery).
+func PropulsionNudgeForRole(role, workDir string) string {
+	var msg string
 	switch role {
 	case "polecat", "crew":
-		return PropulsionNudge()
+		msg = PropulsionNudge()
 	case "witness":
-		return "Run `gt prime` to check patrol status and begin work."
+		msg = "Run `gt prime` to check patrol status and begin work."
 	case "refinery":
-		return "Run `gt prime` to check MQ status and begin patrol."
+		msg = "Run `gt prime` to check MQ status and begin patrol."
 	case "deacon":
-		return "Run `gt prime` to check patrol status and begin heartbeat cycle."
+		msg = "Run `gt prime` to check patrol status and begin heartbeat cycle."
 	case "mayor":
-		return "Run `gt prime` to check mail and begin coordination."
+		msg = "Run `gt prime` to check mail and begin coordination."
 	default:
-		return PropulsionNudge()
+		msg = PropulsionNudge()
 	}
+
+	// Append session ID if available (for /resume picker visibility)
+	if sessionID := readSessionID(workDir); sessionID != "" {
+		msg = fmt.Sprintf("%s [session:%s]", msg, sessionID)
+	}
+	return msg
+}
+
+// readSessionID reads the session ID from .runtime/session_id if it exists.
+// Returns empty string if the file doesn't exist or can't be read.
+func readSessionID(workDir string) string {
+	if workDir == "" {
+		return ""
+	}
+	sessionPath := filepath.Join(workDir, ".runtime", "session_id")
+	data, err := os.ReadFile(sessionPath)
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(data))
 }

internal/session/names_test.go

@@ -1,6 +1,11 @@
 package session
 
-import "testing"
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
 
 func TestMayorSessionName(t *testing.T) {
 	want := "gt-mayor"
@@ -102,3 +107,63 @@ func TestPrefix(t *testing.T) {
 		t.Errorf("Prefix = %q, want %q", Prefix, want)
 	}
 }
+
+func TestPropulsionNudgeForRole_WithSessionID(t *testing.T) {
+	// Create temp directory with session_id file
+	tmpDir := t.TempDir()
+	runtimeDir := filepath.Join(tmpDir, ".runtime")
+	if err := os.MkdirAll(runtimeDir, 0755); err != nil {
+		t.Fatalf("creating runtime dir: %v", err)
+	}
+
+	sessionID := "test-session-abc123"
+	if err := os.WriteFile(filepath.Join(runtimeDir, "session_id"), []byte(sessionID), 0644); err != nil {
+		t.Fatalf("writing session_id: %v", err)
+	}
+
+	// Test that session ID is appended
+	msg := PropulsionNudgeForRole("mayor", tmpDir)
+	if !strings.Contains(msg, "[session:test-session-abc123]") {
+		t.Errorf("PropulsionNudgeForRole(mayor, tmpDir) = %q, should contain [session:test-session-abc123]", msg)
+	}
+}
+
+func TestPropulsionNudgeForRole_WithoutSessionID(t *testing.T) {
+	// Use nonexistent directory
+	msg := PropulsionNudgeForRole("mayor", "/nonexistent-dir-12345")
+	if strings.Contains(msg, "[session:") {
+		t.Errorf("PropulsionNudgeForRole(mayor, /nonexistent) = %q, should NOT contain session ID", msg)
+	}
+}
+
+func TestPropulsionNudgeForRole_EmptyWorkDir(t *testing.T) {
+	// Empty workDir should not crash and should not include session ID
+	msg := PropulsionNudgeForRole("mayor", "")
+	if strings.Contains(msg, "[session:") {
+		t.Errorf("PropulsionNudgeForRole(mayor, \"\") = %q, should NOT contain session ID", msg)
+	}
+}
+
+func TestPropulsionNudgeForRole_AllRoles(t *testing.T) {
+	tests := []struct {
+		role     string
+		contains string
+	}{
+		{"polecat", "gt hook"},
+		{"crew", "gt hook"},
+		{"witness", "gt prime"},
+		{"refinery", "gt prime"},
+		{"deacon", "gt prime"},
+		{"mayor", "gt prime"},
+		{"unknown", "gt hook"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.role, func(t *testing.T) {
+			msg := PropulsionNudgeForRole(tt.role, "")
+			if !strings.Contains(msg, tt.contains) {
+				t.Errorf("PropulsionNudgeForRole(%q, \"\") = %q, should contain %q", tt.role, msg, tt.contains)
+			}
+		})
+	}
+}